AudioCircle
Industry Circles => Tortuga Audio => Topic started by: robertopisa on 8 Mar 2015, 03:30 pm
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Using the description here on how to choose the impedance (from 1k to 99k) of Tortuga's pre
http://www.tortugaaudio.com/ldr-passive-preamps-with-adjustable-impedance/ (http://www.tortugaaudio.com/ldr-passive-preamps-with-adjustable-impedance/)
I prepared a simple spreadsheet that computes the resulting impedance ratio "(Tortuga+amplifier) : source", where R1 is the source impedance, R3 is the amp impedance, and R2 is the wanted Tortuga's impedance (see the yellow cells).
download file Excel (https://mega.co.nz/#!J8kFkB7S!-2YmQVSZNmLCnGIWDX1_H-4CFExECHrMOftDx_QQmvw)
The preferred choice for R2 can be then plugged in Morten's spreadsheet
http://www.tortugaaudio.com/download/Impedance_Attenuation_Schedule_Rev_012215.xlsx (http://www.tortugaaudio.com/download/Impedance_Attenuation_Schedule_Rev_012215.xlsx)
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The tour unit has a pair of V2 boards. I'm not going to swap them out for V2.1's but I am going to upgrade to the 2.1.x firmware and as part of that run both boards through a one-time pre-calibration sequence using precision 0.1% Dale resistors. The non-LDR hardware in each board has enough inherent spec variation such that the auto-cal results can be off for reasons unrelated to the LDRs themselves. Said differently auto-cal may think it's measuring resistance level R when it's really R times some error factor. Pre-calibration is a way of squeezing out some of that inaccuracy. When you step back from all the details, auto-cal is simply an embedded resistance measuring instrument. Pre-calibration is the calibration of that instrument. The net result is a preamp with more precise channel balance which usually translates into better sound stage and stereo imaging. It's all good! :thumb:
Morten,
My LDRx requires ~ 6 pts. balance adjustment. Does my unit need a pre-calibration or is this just the sensitivity of the LDRx adjusting for some inherent imbalance in my system? I did reverse the channels to determine if it was a weak channel in my little digital amp but no difference was detected. I did do this with music, not test tones. Is a 6 pts. adjustment significant?
Is there a breaking period in which the LDRs' equalize?
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Morten,
My LDRx requires ~ 6 pts. balance adjustment. Does my unit need a pre-calibration or is this just the sensitivity of the LDRx adjusting for some inherent imbalance in my system? I did reverse the channels to determine if it was a weak channel in my little digital amp but no difference was detected. I did do this with music, not test tones. Is a 6 pts. adjustment significant?
Is there a breaking period in which the LDRs' equalize?
Off hand that sounds like quite a bit. If you haven't done so recently I'd run it through auto-cal and see if that changes anything. Beyond that I'd recommend first updating to latest firmware (2.1.7) followed by rerunning auto-cal. Even without pre-cal, the 2.1.x firmware renders much better channel balance. Pre-cal is icing on the cake.
LDR's seem to either go bad early on or last a very long time. By "go bad" I mean drift beyond ability to calibrate. Our experience is less than 1% behave this way. Too early to say if that's what is happening.
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Off hand that sounds like quite a bit. If you haven't done so recently I'd run it through auto-cal and see if that changes anything. Beyond that I'd recommend first updating to latest firmware (2.1.7) followed by rerunning auto-cal. Even without pre-cal, the 2.1.x firmware renders much better channel balance. Pre-cal is icing on the cake.
LDR's seem to either go bad early on or last a very long time. By "go bad" I mean drift beyond ability to calibrate. Our experience is less than 1% behave this way. Too early to say if that's what is happening.
Problem solved! :) I ran auto-cal and the channels now balance.
I forgot to to run auto-cal after fooling around with the impedance adjustment function. :duh: IMO the impedance matching adjustment is like the "killer app" in that makes the Tortuga adaptable to almost any setup.
BTW the LDRx works well with the 800 ohm output impedance of my DAC and the amp's 30K input impedance. I tried raising the Tort's impedance to 99k but it was too much. I now run the Tort @ the default 20k. The volume level for listening to music is generally in the 35 pts. to 55 pts. range. My rig has never sounded better. I'm seeing deeper into the music.
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[moved this thread to its own topic]
Glad to hear everything worked out. There's no doubt that setting up a new impedance setting or changing the level of an existing setting is a bit messy. But it does work! :thumb:
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Hello Morten,
can you please say again how to perform a pre-cal? I have a DIY V2 dual-mono boards but pressing the enter button (when Tortuga is off) makes the auto-cal start. Apparently, I have no option to run pre-cal.
I also have some questions that are maybe of interest for people having dual-mono balance V2 boards.
In the previous firmware, 20k impendance was such value for single ended boards, but double value (40k) for dual-mono balanced boards.
Is this the same in the new firmware? If it is so, then dual-mono balanced board has only choices for 2, 4, 6, …, 99x2 with steps of two. I was using 2.5k (which is therefore 5k) but I cannot set it in this way and I have few choices as my amp has input impedance 10k :)
Thanks
-Roberto
Edit. This is what I found in a previous message. Where can I get the resistor module?
Precision pre-calibration process: Using precision temporary plug-in 0.1% Vishay Dale resistor modules it’s now possible to pre-calibrate the auto-cal circuit thus substantially improving the overall accuracy of auto-calibration. This further improves channel balance with commensurate improved stereo imaging and sound stage. We now do this as part of commissioning each V2.1 board prior to running auto-cal. This process is only warranted with new boards or after making hardware changes such as changing opamps. This process is also applicable to existing V2 boards but will require updated software (free download) plus the resistor modules. Tortuga Audio will soon be offering a relatively inexpensive 4-pack of pre-calibration modules as an option when purchase the V2.1 or as a separate purchase (the DIY’er can also build these themselves).
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The bootloader program doesn't recognize the LDR as an USB input? :scratch: Anybody else have this problem?
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It does recognize it. But if I press the enter button, then auto-cal starts. I read that I have to press up/raise three times after that to start pre-cal. I also read that I need the second display, so I will order it.
The bootloader program doesn't recognize the LDR as an USB input? :scratch: Anybody else have this problem?
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The bootloader program doesn't recognize the LDR as an USB input? :scratch: Anybody else have this problem?
The bootloader program does not recognize that it's plugged into the preamp board simply by plugging in the usb cable. You have to put the preamp into bootloader mode. The preamp only enters bootloader mode when power is applied. When you apply power to the board it starts the bootloader code within the board which then waits for only 5 seconds. During those 5 seconds the companion bootloader program running on your PC will see the preamp and you have to press the connect button on the app to lock in that connection. If you don't, the preamp terminates the bootloader code. If you miss the 5 second window you have to pull power from the board, wait a few seconds and then plug power back in.
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It does recognize it. But if I press the enter button, then auto-cal starts. I read that I have to press up/raise three times after that to start pre-cal. I also read that I need the second display, so I will order it.
Sounds like we're confusing topics here. Auto-cal and pre-cal have nothing to do with the USB connection or uploading firmware.
I will provide additional info on pre-cal soon but I strongly caution owners to not mess with precalibration unless that are fully prepared to do so. If you fiddle with pre-cal and do it wrong there's no graceful exit and your board will probably not work right until you get through it correctly.
If you own a v2.1 board there's no need to rerun pre-cal. Owners of v2 boards can improve auto-cal accuracy by doing a one time pre-cal but pre-cal requires 2 different values of precision reference resistors be plugged into the board instead of the LDRs.
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The bootloader program does not recognize that it's plugged into the preamp board simply by plugging in the usb cable. You have to put the preamp into bootloader mode. The preamp only enters bootloader mode when power is applied. When you apply power to the board it starts the bootloader code within the board which then waits for only 5 seconds. During those 5 seconds the companion bootloader program running on your PC will see the preamp and you have to press the connect button on the app to lock in that connection. If you don't, the preamp terminates the bootloader code. If you miss the 5 second window you have to pull power from the board, wait a few seconds and then plug power back in.
I did get the bootloader program going. At first I failed to notice the "detailed instructions"and just plugged in the USB cable. :oops:
I had a bit of trouble getting the bootloader to start. It took at least three tries. It seemed like you had maybe 3 seconds to press the connect button. Even if I pressed the connect button within the 5 second time period, the program didn't load consistently. Nevertheless, it did load and the download was successful. :thumb: Next time it'll be easier for me.
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There's a growing body of evidence that the improved accuracy of the autocal algorithm makes the quality of the power supply to the LDR3x board very important. During autocal the LDR3x board is acting as a closed loop measurement system involving 4 12 bit DAC channels, 3 op amps, and 4 analog-to-digital converter channels. So no big surprise that the better (cleaner, less noise) the PS, the easier it is for autocal to function properly.
Once upon a time I said that you could run the LDR3x off of most any 12V wall-wart style PS and while that remains true for normal running of the LDR3x board, it's not true when it comes to autocal where the presence of noise is more critical. With adjustable impedance relying heavily on autocal to work properly a clean power supply is more important than ever.
Going forward I am recommending that the LDR3x be powered either with a regulated linear power supply, or a high quality switch-mode power supply either of which are capable of supplying 12 VDC with 20 millivolt or less of ripple/noise and certainly none of the wild voltage spikes that are typical of many cheap SMPS "wall-wart" style power supplies. High frequency (above 100 kHz) low level noise from SMPS's is not a problem. We use a nice little SMPS dc-dc converter that produces clean +/- 10 millivolt power so it's not a linear vs. SMPS issue. It's a clean vs. noisy power supply issue.
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Just received my LDR3v2 and would like to understand the charts that robertopisa and Morten have supplied. My current source has about 100 ohm output impedance and one amp has 20k input impedance and another amp I have has 50k input impedance.
Anybody know what my impedance # on the LDR3v2 should be selected to? And how do you come to that?
Thanks,
Tom
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I suggest setting the 5 presets to 10, 20, 40, 60, and 80 like I did. You can run through them while listening to your most revealing and familiar tacks to hear the best setting.
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I suggest setting the 5 presets to 10, 20, 40, 60, and 80 like I did. You can run through them while listening to your most revealing and familiar tacks to hear the best setting.
Ok, I've done some of those with 20 sounding the best so far..will the others. Thanks!
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How does impedence selection work, for example the cdp xlr output impedence is 40 ohm and 4.8v rms.
I have measured a resistor at just before the xlr plugs at 10 ohm and 0.2ohm to ground, technically running this into the tortuga , what are the best resitors values?
Can and should the 10 ohm resistor be completely removed, or will increasing the value to 100 ohm or higher be more optimal into the tortuga?
This should be the i/v stage resistors at the cdp output?
I'm a little lost in what impedendece setting does.
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How does impedence selection work, for example the cdp xlr output impedence is 40 ohm and 4.8v rms.
I have measured a resistor at just before the xlr plugs at 10 ohm and 0.2ohm to ground, technically running this into the tortuga , what are the best resitors values?
Can and should the 10 ohm resistor be completely removed, or will increasing the value to 100 ohm or higher be more optimal into the tortuga?
This should be the i/v stage resistors at the cdp output?
I'm a little lost in what impedendece setting does.
While I'm not familiar with all the resistor options you apparently have with your CDP what matters is achieving a sufficient impedance bridging ratio between you CDP and you amp such that the CDP doesn't have to work all that hard (i.e. supply much current) in order to the deliver the audio signal (i.e. the AC voltage) to the amp. If your amp has say a 10k input impedance and your CDP has 10 ohm output, that's a 1000:1 ratio. Increasing the CDP to 100 out gives you 100:1. I would argue anything beyond 50:1 is more than sufficient. Increasing it further is unlikely to yield any improvement in sound quality.
Putting a resistive passive preamp between your source and amp complicates matters because the preamp and amp act as parallel resistors such that their combined resistance is always less than each by itself. The adjustable impedance feature introduced with version 2.1.X firmware for the Tortuga preamps provides some degree of latitude to affect this overall combined impedance to optimize sound quality. If you already have sufficient impedance bridging I would argue that the adjustable impedance feature will not likely improve matters.
The recent article we published on Adjustable Impedance provides some fairly good background on this subject. Here is the article: http://www.tortugaaudio.com/ldr-passive-preamps-with-adjustable-impedance/ (http://www.tortugaaudio.com/ldr-passive-preamps-with-adjustable-impedance/)
Cheers,
Morten
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A few thoughts on adjustable impedance.
My own impressions from using the adjustable impedance feature at various impedance levels (at least with our development audio gear) is that I can't discern much if any difference. The SS amp we use has a 20k input impedance and the LDR preamp has a nominal impedance input of 20k. Below 10k I can tell things start to lean out but going to 30, 40 or 50k seems to make no difference. I did convince myself that jumping it up to 99k did improve things just a bit.
I've heard back from a couple of customers with balanced units where pushing up the impedance much above 50k begins to exacerbate any DC offset that may be present and thus can introduce hum or even cause amps that have DC offset protection to trip. Keeping in mind that with balanced units 50k is really 100k and 99k would be 198k. This suggests that too high of an input impedance carries its own set of issues. DC offset may benefit from lower impedance where more DC signal current gets shunted to ground.
I suspect that once you achieve a sufficient bridging impedance ratio (amp input Z vs. source output Z), increasing it doesn't really buy you additional benefit.
I'm inclined in the next firmware release to leave in adjustable impedance but have only 1 setting and not 5. This would free up some code space for some other things that need updating. We're beginning to bump into the upper limits of the chip's programming capacity so have to be more judicious about what goes in and what might have to come out.
If any of you have tried the adjustable impedance feature I would encourage you to share you thoughts.
Cheers,
Morten
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Like you, I heard little or no difference going into a tube amp. and maybe... just maybe... 99 sounded a bit tighter.
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I agree with you. I am using 2K (which is 4K) with my balanced unit. This was better than 10k (which is 20k). Also 1 setting is enough for me. After I decided which is the right impedance, it is just a waste to keep 5 settings. The important feature is that we can change impedance in that setting.
The space you get free could be used to improve the ergonomics of the Apple remote. Too many functions overloading it. Maybe you should activate them only after pressing the encoder for 30 seconds. Normal use would leave just the basic functions (raise & lower volume, input selection, balance, mute). Just my 2 cents :)
A few thoughts on adjustable impedance.
My own impressions from using the adjustable impedance feature at various impedance levels (at least with our development audio gear) is that I can't discern much if any difference. The SS amp we use has a 20k input impedance and the LDR preamp has a nominal impedance input of 20k. Below 10k I can tell things start to lean out but going to 30, 40 or 50k seems to make no difference. I did convince myself that jumping it up to 99k did improve things just a bit.
I've heard back from a couple of customers with balanced units where pushing up the impedance much above 50k begins to exacerbate any DC offset that may be present and thus can introduce hum or even cause amps that have DC offset protection to trip. Keeping in mind that with balanced units 50k is really 100k and 99k would be 198k. This suggests that too high of an input impedance carries its own set of issues. DC offset may benefit from lower impedance where more DC signal current gets shunted to ground.
I suspect that once you achieve a sufficient bridging impedance ratio (amp input Z vs. source output Z), increasing it doesn't really buy you additional benefit.
I'm inclined in the next firmware release to leave in adjustable impedance but have only 1 setting and not 5. This would free up some code space for some other things that need updating. We're beginning to bump into the upper limits of the chip's programming capacity so have to be more judicious about what goes in and what might have to come out.
If any of you have tried the adjustable impedance feature I would encourage you to share you thoughts.
Cheers,
Morten
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The space you get free could be used to improve the ergonomics of the Apple remote. Too many functions overloading it. Maybe you should activate them only after pressing the encoder for 30 seconds. Normal use would leave just the basic functions (raise & lower volume, input selection, balance, mute). Just my 2 cents :)
Good point and good idea! Will give this some thought.
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Morten,
The adjustable impedence is great and hope you leave 3 adjustments.
I have mine, balance unit set at 39, 41 and 43. At these steps, It makes all difference to give a little more naturalness at 39 and more bite at 43. Overall i use setting at 41.
Initially tested at intervals of 5 which i found too large a jump. This feature is excellent to adjust according to various recordings, a bare minimun i would say is 2 settings.
I also found the apple remote, really nice but a tad small and sometimes pressed the left right button. It would be cool to have a double click to enter the settings mode, power on/off. Volume and mute would be the most used and disabling the rest with a double click would seem most user friendly.
Thanks for the great work and product.
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Morten,
The adjustable impedence is great and hope you leave 3 adjustments.
I have mine, balance unit set at 39, 41 and 43. At these steps, It makes all difference to give a little more naturalness at 39 and more bite at 43. Overall i use setting at 41.
Initially tested at intervals of 5 which i found too large a jump. This feature is excellent to adjust according to various recordings, a bare minimun i would say is 2 settings.
I also found the apple remote, really nice but a tad small and sometimes pressed the left right button. It would be cool to have a double click to enter the settings mode, power on/off. Volume and mute would be the most used and disabling the rest with a double click would seem most user friendly.
Thanks for the great work and product.
I've spent the better part of the past 2 days overhauling the software trying to simplify/reorganize/separate the primary control functions from the more complex and less often used (like impedance, auto-cal, pre-cal etc. ).
While it's possible to come up with an alternative to the current system I've concluded it would only end up being different but not fundamentally better. And all the changes would end up confusing all of us who have gotten used to how the Apple Remote currently works with the LDR preamps. So I'm not going to change the way the current controls work. All of which is fairly well documented now in the online documentation.
The key issue comes down to this. The 7 button Apple remote is not ideally suited for all the control functions its being asked to manage given the simple numerical display available. I think a much more sophisticated numerical/graphical display with menus etc. would work well with the Apple remote. Alternatively a custom remote with several additional buttons would accomplish the same thing essentially providing the same advantage of a more complex display. I don't believe you would need both a sophisticated display AND a more complex remote.
All possible options for the future. The simplest approach would be a custom remote but this is also costly to develop because of the quantity you need or order to get the unit price down. The Apple costs $20-25 and for us that's just a pass through cost - we make nothing on that item. I'd probably have to charge around $100 to justify a custom remote. Does that seem reasonable I wonder?
Another advantage of the custom remote is it could be made compatible with existing owners with V2 and V2.1 model boards/products by uploading a simple firmware update.
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Morten
Have you considered developing a phone app to drive via bluetooth? Then a true GUI could be used to drive and configure the passive pre, and configuration data comes back the other way (volume, balance, impedance, input selected etc).
Craig
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If you supported one or more standard sets of remote codes, then the user can use a programmable remote set to those codes. I got one on Amazon for $5.
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Morten
Have you considered developing a phone app to drive via bluetooth? Then a true GUI could be used to drive and configure the passive pre, and configuration data comes back the other way (volume, balance, impedance, input selected etc).
Craig
Bluetooth is on the short list of possibilities for the next version but I don't think it's viable to retrofit that into the existing design. Too many additional control inputs/outputs needed for which there's no I/O real estate available. Or for that matter software real estate. But Bluetooth hardware modules have really come down in cost ($10 or less for simple versions) and are fairly simple to interface with. And practically all smartphones/tablets have Bluetooth now so custom iOS/Android apps would be very doable.
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If you supported one or more standard sets of remote codes, then the user can use a programmable remote set to those codes. I got one on Amazon for $5.
We have published the basic command codes for our original Tortuga Audio remote. They are in our documentation section (http://www.tortugaaudio.com/documentation/#document-5 (http://www.tortugaaudio.com/documentation/#document-5)) which use the 38khz NEC IR protocol. We didn't publish the Apple commands but they use the same NEC protocol but use somewhat more complex commands.
I've looked around for generic remotes that could be programmed with specific command sequences but have no luck finding any. Yes, there are plenty of remotes you can teach by pointing an existing remote at them and pressing a key. But what if you don't have that remote and want to program in specific known key codes? If you or anyone else out there know of such remotes I'm all ears.
Cheers,
Morten
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I've looked around for generic remotes that could be programmed with specific command sequences but have no luck finding any. Yes, there are plenty of remotes you can teach by pointing an existing remote at them and pressing a key. But what if you don't have that remote and want to program in specific known key codes? If you or anyone else out there know of such remotes I'm all ears.
I guess I don't really follow. If a remote says that it generates (say) NEC codes, then won't the codes sent over IR be the same for all the common keys - 0-9, Mute, Vol up/down, Channel up/down - regardless of the specific remote? If not, I guess I don't understand how these remotes could be useful.
Anyway, it's an idea... :)
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I guess I don't really follow. If a remote says that it generates (say) NEC codes, then won't the codes sent over IR be the same for all the common keys - 0-9, Mute, Vol up/down, Channel up/down - regardless of the specific remote? If not, I guess I don't understand how these remotes could be useful.
Anyway, it's an idea... :)
The world of IR remote communications is at once both simple and a complex mess. The good news is it works.
The trouble starts with a lack of universal language. Sony has their protocol, Phillips developed their own (RC-5) and then the Japanese developed their own - NEC. These are like French, German and English. All good languages. All very different. We use NEC as does Apple. So Tortuga only speaks NEC and is illiterate in the others.
Not only do you have multiple languages but it comes down to what each is saying. To a large extent the actual value/number transmitted when a key is pressed on a given remote can be anything the designer wants it to be. In fact it could be a whole string of numbers/letters for each key press plus also a unique ID number so that a given remote only talks to (or is heard by) a device with the same matching ID number. Hence the need to sometimes "pair" a remote up with the device it's controlling as it the case with our preamps and the Apple remote which has 256 different possible ID numbers. It gets more complicated. The meaning of some buttons may depend on what button was pressed immediately before it. Some buttons generate a single message. Some buttons generate multiple messages.
The evolution of "Universal Remotes" is actually quite an accomplishment but you have to program in every blessed command sequence for every device in whatever language it uses. There are 10's of thousands of devices. Yikes!
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As we accumulate more experience with the adjustable impedance I continue to be surprised by some of things this feature has revealed.
Since the release of the V2.1 design and firmware, we've been shipping all our preamps with the default impedance set at 20k which for balanced units means effectively 40k. Usually that's been ok for balanced units.
However, a recent LDRxB balanced preamp customer reported annoying ground loop hum with the preamp connected to a CD source but much less so when connected to a Tuner. After confirming that that the unit was indeed set at 20k (40k balanced) I advised reducing the impedance to 10k (20k effective). After running the unit through auto-calibration at this reduced impedance level the hum issue was no longer evident and everything sounded great.
I'd received previous feedback from another LDRxB owner who did extensive testing at different impedance settings that he could raise impedance high enough to cause audible hum and at least in one instance sufficient DC offset to trip a safety circuit on an amp. Again, reducing the impedance setting made all these symptoms go away and the preamp performed very well.
Also to my surprise an owner of dual LDR3x.V2 boards in a balanced DIY preamp determined that the optimal impedance setting for his system was somewhere around 2-5k (4-10k balanced).
In yet another example a LDR1.V2B owner substituted his preamp for high end SS active and was able to demonstrate various impedance settings on-the-fly which revealed that the DAC/AMP combination really liked a lower impedance than offered by the active preamp. This was evident in overall improved sound quality and specifically reduced high end brightness.
In ways that I hadn't anticipated I'm really pleased to see that the adjustable impedance lends a degree of flexibility to optimize each preamp for the system it's connected to. Also, we're probably going to change the default impedance on new balanced preamps from 20k to 10k (20k effective) - same as our single ended units.
Cheers, :thumb:
Morten
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Several customers have run afoul of the Adjustable Impedance feature - at least as it's currently designed/controlled - wherein they accidentally switch from the default impedance setting (#1 - 20k) to say setting number 2. No harm in that per se but if you switch the preamp to a setting number that hasn't been configured yet...you get...well....nothing. As in no sound at all. Zero. Zip. Nada.
This has a magical way of making our phone ring.
Cust: "Hi, my name is _______ and I recently bought your _______ preamp and it suddenly stopped working."
Me: "What do you mean it stopped working?"
Cust: "Well, there's no sound coming out."
Me: "Is it on?"
Cust: "Yes, it's on."
Me: "Are the displays working?"
Cust: "Oh yeah, everything looks and acts normally but there's no sound. And it was working great a moment ago. Sounds great by the way."
Me: "Are you at the unit now. Do you have the remote handy?"
Cust: "Yep"
Me: "Press the left button on the remote and tell me what number show up."
Cust: "Ok. Ah...2!"
Me: "Have you configured any of the impedance settings 2-5 since you first received the unit?"
Cust: "No. I was planning on messing with that next but I was enjoying listening to it and hadn't gotten around to it yet. And then it stopped working."
Me: "Ok. Press the down button on the remote to change the impedance setting back to 1."
Cust: "Heh! That fixed it!! It's back on! What happened? "
Me: "You'd accidentally switched from impedance setting #1 which is the default setting number and switched the unit to #2. Since #2 hadn't been configured yet, there's no attenuation table established so no sound comes out. Basically the unit is muted. If you switch it back to #2, then adjust the impedance level (1-99k), press enter, turn it off, and then run auto-cal, that will set up setting number 2. Same from settings 3-5. At that point you can switch back and forth between impedance settings on the fly with live music and home in on the optimal setting for your system. "
Cust: "Ok, great. Thanks."
Me: "You're welcome. Enjoy. Bye."
Cheers,
Morten :thumb:
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I had to laugh when I read this post. If you want to fill in the blank above, the name is Bill. I'm the one who called and prompted the post. I'm sure it was me because Morten accurately related our conversation word for word (while protecting my privacy, of course). I thought there was a chance the problem was "faulty operator" and I would sort it out on my own eventually (RTFM anyone?) but in my frustration I chanced a call to Tortuga. I wasn't sure I'd get to talk to Morten or get an answer at all since it was a bit after hours, Florida time. Morten answered the phone himself and cheerfully but carefully talked me through the troubleshooting steps. It took just a few minutes to get me back up and running. The purpose of this post is to publicly thank Morten for a great product and superb customer service. If you are looking for a completely transparent preamp at a reasonable price and would prefer to buy from a company that offers terrific support then look no further. Tortuga is the answer.
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I had to laugh when I read this post. If you want to fill in the blank above, the name is Bill. I'm the one who called and prompted the post. I'm sure it was me because Morten accurately related our conversation word for word (while protecting my privacy, of course). I thought there was a chance the problem was "faulty operator" and I would sort it out on my own eventually (RTFM anyone?) but in my frustration I chanced a call to Tortuga. I wasn't sure I'd get to talk to Morten or get an answer at all since it was a bit after hours, Florida time. Morten answered the phone himself and cheerfully but carefully talked me through the troubleshooting steps. It took just a few minutes to get me back up and running. The purpose of this post is to publicly thank Morten for a great product and superb customer service. If you are looking for a completely transparent preamp at a reasonable price and would prefer to buy from a company that offers terrific support then look no further. Tortuga is the answer.
:lol: Thanks for the kind words Bill. If it's any consolation I've had a few calls like yours recently so thought I'd float a public service announcement. And thanks for the script! :green:
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I would really opt for leaving at least 2 impedance registers in place for future releases.
The optimum value I have found in my system is unexpectedly high: 65k
The source is a Schiit Yggy and the amps are Bottlehead Paramounts with 250k input impedance.
The difference I hear from 65k to either lower or even higher values is that the sound loses focus.
That's regarding as well soundstage and tonal balance.
Norbert
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I would really opt for leaving at least 2 impedance registers in place for future releases.
The optimum value I have found in my system is unexpectedly high: 65k
The source is a Schiit Yggy and the amps are Bottlehead Paramounts with 250k input impedance.
The difference I hear from 65k to either lower or even higher values is that the sound loses focus.
That's regarding as well soundstage and tonal balance.
Norbert
From all the feedback we've received we'll probably leave the 5 settings in the future. Not really needed for day to day use but very helpful in dialing in the optimal setting.
It's been a revelation hearing back from people in terms of optimal impedance levels. They've ranged everywhere from just a few k up to 99k and everywhere in between. Since adjustable input impedance is not something you can normally change on audio components it's not something you would think could make much of difference. And in all fairness sometimes it doesn't. But then sometimes it does...even counter-intuitively. From a designer perspective the assumption is that all you need is enough and that raising the impedance further can drive up distortion. But as with many elements of high performance audio there seems to be all manner adjustments and tweaks that can and do make a difference. Makes this hobby all that more interesting...and sometimes even bewildering. :thumb:
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Hi Norbert,
Thanks much for your experience with the Tortuga's variable input impedance with the Yggy. I have that DAC on order for an evaluation. I've also found that once I've dialed in the optimum impedance for a DAC, even changes of 2k at a time (using my LDR1B) are audible.
I'm currently using the PS-Audio PerfectWave Mk-II DAC and use either a setting of 8 or 9 on the LDR1B which gives a net impedance of 16k or 18k. Once I get above 20k the sound starts to veer toward the lean side. Below 16k, it becomes more lush (almost tube-like), but to my ears a bit too bloomy and a touch less clean on top. My suspicion is that the output stage of the DAC may not like that low of an impedance.
Some other DACs like the EMM Labs DAC2X seem to like a higher impedance load. A highly rated preamp with a fixed 20k input impedance was easily bested by the LDR1B once I set its input impedance to 40k to 50k.
Now that I have the capability of fine tuning input impedance with the Tortuga, I've come to think of that as a necessary feature on a preamp to get the most out of a system. Who would have thought?
I'll post my experience with the Yggy/LDR1B combo.
Best,
Robert
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Hi Morten & Robert,
your posts above let me wonder what we are really experiencing here. Is it the distortion of the LDRs changing with impedance level? Or is it the impact of the output stage of the source we are using?
When using my phono setup (DIYHIFISUPPLY LCR Cole) I do get the same optimum value (65k) as with my Yggy. I think the difference in technology could not be bigger. I don't know exactly what the Yggy's output stage looks like, but I guess it uses DC-coupled servo-controlled output stages uing JFETs (that's what Schiit tells us) resulting in a close to zero output impedance.
The Cole uses a E88CC triode charged by a CCS running at 14mA coupled to the output by a 2,2uF capacitor which should result in a 3 to 4k output impedance.
Could be that the listening level plays a role here? Mine is between 35 and 45 (-28 to -18dB) where you are roughly running on a 1 : 10 relationship regarding the resistance of the upper and lower LDR.
@ Morten: Is there a "best sound zone" relating to the resistance of the LDRs?
Best regards,
Norbert
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Hi Morten & Robert,
your posts above let me wonder what we are really experiencing here. Is it the distortion of the LDRs changing with impedance level? Or is it the impact of the output stage of the source we are using?
When using my phono setup (DIYHIFISUPPLY LCR Cole) I do get the same optimum value (65k) as with my Yggy. I think the difference in technology could not be bigger. I don't know exactly what the Yggy's output stage looks like, but I guess it uses DC-coupled servo-controlled output stages uing JFETs (that's what Schiit tells us) resulting in a close to zero output impedance.
The Cole uses a E88CC triode charged by a CCS running at 14mA coupled to the output by a 2,2uF capacitor which should result in a 3 to 4k output impedance.
Could be that the listening level plays a role here? Mine is between 35 and 45 (-28 to -18dB) where you are roughly running on a 1 : 10 relationship regarding the resistance of the upper and lower LDR.
@ Morten: Is there a "best sound zone" relating to the resistance of the LDRs?
Best regards,
Norbert
As impedance goes up there will be a corresponding increase in LDR distortion as the voltage drop increases across each LDR for a given volume setting. My understanding is the absolute levels are still too low to be perceived but that's certainly not a definitive view. The listening level range (step 35-45) is quite typical which says that for most source/amp combinations (voltage output vs. amp sensitivity/power), that's the amount of voltage division needed to attain reasonable volume levels. I don't have an informed view as to whether there's a "best sound zone" with the LDRs.
Your point about the 2 sources having very different output stage types and impedances is interesting since 65k on the preamp seems to be optimal for either. With the 250k bottleheads the effective parallel impedance seen by the source is ~52k. For the Cole at 3-4k out that's only a 13-17:1 bridging ratio which is arguably low for a passive while for your DAC the bridging ratio is darn near off the charts high.
This underscores the "soft" nature of the impedance matching guidance for our passive preamps where we suggest 50:1 to be on the safe side. It really comes down to how robust the output stage is in your source when mated with a given amp.
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I have a question. I recently added the Tortuga LDR preamp to my system which is currently: Schiit Yggdrasil to Tortuga passive pre to 301 DHT buffer to First Watt SIT2. I also have a powered sub running out of the LDR pre. The 301 Pre has the volume pot all of the way up.
Do you think that it would be better to put a splitter on the output of the 301 Pre and let it drive both the SIT and the sub or else leave things as they are?
It seems to me that if the 301 is up to the task it might be better to let it do the buffering duties rather than having the DAC push both via the LDR. The SIT2 has an input impedance of 100k and the sub is 47k.
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I have a question. I recently added the Tortuga LDR preamp to my system which is currently: Schiit Yggdrasil to Tortuga passive pre to 301 DHT buffer to First Watt SIT2. I also have a powered sub running out of the LDR pre. The 301 Pre has the volume pot all of the way up.
Do you think that it would be better to put a splitter on the output of the 301 Pre and let it drive both the SIT and the sub or else leave things as they are?
It seems to me that if the 301 is up to the task it might be better to let it do the buffering duties rather than having the DAC push both via the LDR. The SIT2 has an input impedance of 100k and the sub is 47k.
From the standpoint of the DAC, driving multiple amps out of a buffer (which the DAC won't "see") will almost always be preferred to running multiple parallel amps from a resistive passive (which the DAC will see).
If I had your set up I'd try all possible variations and note the differences if any. I think we'd all enjoy getting your feedback on that.
1) No buffer - both amps off of Tortuga preamp
2) Buffer - main amp off pre, sub off buffer
3) Buffer - main amp off buffer, sub off pre
4) Buffer - both main & amp off buffer
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Hi Morten,
Impedance setting may well be one very and perhaps underused and not well understood by us users.
I have previously mention once I felt I had the right impendace, an adjustment just by 1 changed the sound by a large degree.
I think now with more understanding of it with different sources and music, I will be using it much more.
Morten,
I have mine set at 43, which has the best sound.Once I go any lower the sound mellows out too much.
The interesting thing also is that go up by 1, makes the sound more brilliant, tight and harder sounding. This also make the sound louder as compared with the lower setting just by -1, this is at 42. But if I go -2 (41)instead, it is still softer than impedanceat 43, but not as soft as at 42.
Is this normal?
The sweetspot of 43, though softer and I need to compensate volume up by around +2, but at this setting, all digital hardness and glare vanishes! This alone is priceless.
Is this normal?
Please remove the post in the wrong thread.
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Morten,
To add on...
Does the quality of power supply affect the calibration?
I have 2 settings of the same impedence i.e 42, one done some time ago with a battery and another by low noise power supply.
They actually distinctly sound different!
I am not sure what is happening here.
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The interesting thing also is that go up by 1, makes the sound more brilliant, tight and harder sounding. This also make the sound louder as compared with the lower setting just by -1, this is at 42. But if I go -2 (41)instead, it is still softer than impedanceat 43, but not as soft as at 42.
Is this normal?
The sweetspot of 43, though softer and I need to compensate volume up by around +2, but at this setting, all digital hardness and glare vanishes! This alone is priceless.
Is this normal?
The question of what is "normal" when it comes to adjustable impedance is an interesting one. To begin with adjustable impedance isn't normal. I know of no other preamp that has this feature. And no doubt many designers would argue that it's not necessary or beneficial. We implemented it because our preamp design is software driven and therefore it's possible to do this. Like the mountain, we climbed it because it's there....and we could. As people play around with this feature some find no benefit while others are able to find an optimal setting that clearly improve the sound. I would not have guessed that minor adjustments would make much difference.
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Does the quality of power supply affect the calibration?
I have 2 settings of the same impedence i.e 42, one done some time ago with a battery and another by low noise power supply.
They actually distinctly sound different!
I am not sure what is happening here.
Yes. In fact power supply is most important during calibration and arguably much less so during normal operation. During calibration, the preamp is actually a closed loop measurement system where DACs generate voltages that are passed through LDRs with the results measured by ADCs.
That said, it's not immediately obvious to me why the results would sound distinctly different. It could be that one calibration data set is a 1 or 2 dB louder than the other and so the perception is a difference which may only be a matter of volume. Then again, there are numerous variables working here so I wouldn't expect identical results.
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Does this point to impendenca has an effect on volume. I find that lower impendence to sound softer mellow, yet more natural and relaxing.
I really dont understand impendence, but is does alter the electrical voltages and thus affects drive.
This is intriguing to the possibilities of further tuning.
We discussed previously on low noise psu in which I had used a tps74, I had switch this out for another low noise reg. I recall I possibly did a recal using batteries for that 1 setting, thus with a different regulator.
While music is on and toggling the impedence setting on the fly, I clearly hear the differences.
A friend was baffled how I could change the sound, it sounds as if I had change a different power cord all together.
If I go down another point which used the old regulator previously doing the autocal, there is a resemblance in the sonics percular to the autocal done then, I am almost afraid to repeat the autocal in fear I may lose the familar sound I was getting.
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Does this point to impendenca has an effect on volume. I find that lower impendence to sound softer mellow, yet more natural and relaxing.
I'm baffled how such small changes in the resistance setting of the Tortuga results in such noticeable changes in sound quality. Now I can hear the difference between 20k, 50k and 100k, but that is probably more to do with the output resistance of the Tortuga producing additional attenuation when loaded by the power amp input resistance. Suppose you listen at 50 on the display, with a nominal attenuation of 14.32dB. Suppose for the moment that the input resistance of the power amp is 100k (many are lower than this).
At 20k, the amp loading reduces the volume (as compared with no loading) by 0.27dB. At 50k by 0.65dB and at 100k by 1.26dB. So you have to be very careful how you interpret what you are hearing when you switch the Tortuga between resistance settings on the fly. The odd dB shift in volume is clearly audible, and easily interpreted as it sounding softer. If you can hear the effect of changing in 1k increments something odd is happening.
Have you done a blind trial with other listeners? Do they hear the same thing as you?
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It is my understanding that the adjustable impedance of the Tortuga affects the source, not the output to the amp. The higher the setting, the less stress put on the output of the source (most cases a DAC). Morten can correct me if I'm wrong.
My DAC seems to like a very low setting. 20k is good, but 10k and even 5k produce better transparency and dynamics. As I increase the impedance to 40k, 60k, 80k, and 99k, the sound softens, loses dynamics, and even colapses the sound stage. 99k is not listenable for me.
In all of my testing, I never heard significant changes with small impedance changes. But every source can behave differently. I do know consistency is key. If you run a calibration sequence with different power supplies, you can expect more volume changes between calibrations. I would rerun all calibrations that are not done with the same power supply.
I hope I'm correct with my statements. If not, then I'll need a refresher in how this works. :green:
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In my setup, 1-2 steps ether up or down is clearly audible. The lower the setting at the sweetspot makes a nice and noticeable difference.
At other settings outside this sweetspot, it was not really audible, nor would i bother.
I know for a fact the autocal on a different psu seems to contribute this this effect.
Presently, i am delighted with the sonics now, so do not want to recal until it is really needed and as there isnt enough spare slot to auto the new psu.
I dont want to lose the old setting either, i tried 1 recal and it is indeed different sounding.
The db difference is also noticeable, but more so when you have the sweetspot setting, the wrong setting doesnt nearly sound as good and difficult to distinguish from slight adjustments.
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Morten - here's a thought for those who know the input resistance of the amplifier that follows the Tortuga. In the new design, if there was an option to input that resistance, then loading-induced loudness changes could be accurately compensated for by a change in attenuation.
In that way decoupling loudness changes from sonic changes could be done.
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It is my understanding that the adjustable impedance of the Tortuga affects the source, not the output to the amp. The higher the setting, the less stress put on the output of the source (most cases a DAC). Morten can correct me if I'm wrong.
I had assumed that changing the input impedance would automatically change the output impedance too. This is very interesting!
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Well yes it does. But the effective output resistance is the actual output resistance of the Tortuga in parallel with the input resistance of the power amp (or whatever) it is connected to. Which changes the attenuation.
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I had assumed that changing the input impedance would automatically change the output impedance too. This is very interesting!
Yes and no. Input is nearly fixed for any given impedance level whereas output impedance varies as you change volume (attenuation).
Input Impedance
Whether it's a potentiometer or a pair of series/shunt LDRs, what you have is a voltage divider. With pots the input impedance is always fixed. It's the rated resistance of the pot from input to ground which per the sketch below is Ra+Rb. Ground is the bottom horizontal wire and the wire coming out between Ra and Rb is the pots wiper ...OR.. the output of the voltage divider (same thing).
With LDRs is can also be fixed but not necessarily. It depends on how you control the LDRs. In the sketch the series LDR is Ra and the shunt is Rb. Again, it's the sum of Ra and Rb that determines the input impedance. Unlike with a pot where this sum is fixed, with LDRs you must control each of these independently. Which we do in our LDR preamps.
The way a voltage divider works is per this formula: Vout = Vin x Rb/(Ra + Rb) or Vout/Vin = Rb/(Ra + Rb). The resulting attenuation expressed in decibels is dB = 20*log(Vout/Vin)
What we do in our LDR preamps where you can change the input impedance is we compute the combinations of Ra and Rb that give us the 70 attenuation steps we need while trying to maintain the sum of Ra + Rb equal to the target input impedance. In practice this is not possible while also attenuating down to -60 dB so what happens is the impedance has to go up from the target as volume gets turned down low (usually around step 20 and down).
(http://www.audiocircle.com/image.php?id=139284)
Output Impedance
Output impedance is different. It's not fixed. Not in a pot and not with LDRs either. The way to look at output impedance is just flip it around and look at it as though it was just another input impedance with the output jumpered. That's illustrated below.
Unlike with input impedance where Ra and Rb were in series, here Ra and Rb are in parallel. With parallel resistors(impedances) the formula is R = Ra x Rb/(Ra + Rb)
(http://www.audiocircle.com/image.php?id=139283)
Tying all of this together you get something like the graphic below. This shows an attenuator with 20k input impdance - the green line. Note that it's constant until you get down to around -50 dB and then it increases in order for the attenuation to continue down to -60 dB. It's just how the math works.
Now note the output impedance which is the yellow line. As volume increases it rises from a very low value (100 ohms) and then peaks at -6 dB (loud! ) and abruptly falls back down to 100 ohms as attenuation approaches 0. This is how every pot works in every preamp ever.
(http://www.tortugaaudio.com/images/impedance_atten_curves_log1.jpg)
Of course all the above is simply looking at the attenuator in isolation and not hooked up to anything. When you attach an amp to the output of the attenuator you add an additional resistance in parallel. So you have to do the R = Ratten x Ramp / (Ratten + Ramp) calc to get the effective impedance as seen by your source (DAC, phono preamp etc. )
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I recently just installed my new Tortuga attenuator. I find that for my system the best impedance setting for my balanced unit is about 30. Lower or higher settings result in unbalanced stereo channel volumes requiring significant channel balance adjustment. In fact, before I adjusted the impedance to 30 most of the sound was coming from only one speaker and I thought my system had a broken component. When I tried different impedance values from minimum to maximum the center focus was only correct at around 30 to 35 where the volume of the two channels is about equal. This is also where the sound is most open and dynamic and neither too thick nor too lean. This surprised me because the Goldpoint balanced attenuator I replaced with the Tortuga unit had a fixed impedance resistance of 10k and had only a slight mismatch of volume between stereo channels. Fortunately, the Tortuga's impedance adjustability allows it to perform optimally in my system. At setting 30 it sounds superb.
I am still experimenting with the impedance adjustment to
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To complete the unfinished sentence in my last message, "I'm still experimenting with the impedance adjustment to" determine if a value slightly under 30 or slightly over 30 results in the best sound. Intuitively, a digit or two either direction should not make an audible difference, but posts by others say they can hear differences by changing the impedance value by only one unit.
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There should be no balance issues. Are you running auto calibration after each change to the impedance? If not, that's the issue.
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After each impedance assignment I ran Auto Cal. I did this separately for each of the following assignments: 1-10k, 2-20k, 3-30k, 4-40k and 5-50k. The last Auto Cal followed the 50k assignment to setting 5. When listening and changing the settings from 1 to 5 (10k to 50k), only 30k has the correct balance. Maybe I'm not doing Auto Cal correctly. When I change the impedance for a particular setting I then turn off the preamp, turn off the source, and then press the center button on the preamp remote to initiate Auto Cal and let it do its thing until the unit shuts itself off automatically.
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After each impedance assignment I ran Auto Cal. I did this separately for each of the following assignments: 1-10k, 2-20k, 3-30k, 4-40k and 5-50k. The last Auto Cal followed the 50k assignment to setting 5. When listening and changing the settings from 1 to 5 (10k to 50k), only 30k has the correct balance. Maybe I'm not doing Auto Cal correctly. When I change the impedance for a particular setting I then turn off the preamp, turn off the source, and then press the center button on the preamp remote to initiate Auto Cal and let it do its thing until the unit shuts itself off automatically.
There shouldn't be noticeable changes in channel balance between impedance settings. I've not observed this behavior before nor has it been mentioned prior to this instance. It makes my wonder if there's some kind of interaction between the preamp and the either the source's balanced output stage or the amp's balanced input stage such that changing the impedance somehow skews the channel balance. If so then this may have more to do with the design of the respective balanced input/output stages rather than a true left/right channel balance with the preamp. Some balanced input/output designs are less robust than others and can be influenced by external impedances/loads. Not a very satisfying response but at least you were able to find a sweet spot where it all works and sounds best.
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You might try swapping your source inputs at the Tortuga (left/right) while at an impedance setting where you hear an imbalance. If the imbalance then switches to the other channel, that would seem to indicate that one of the source's channels doesn't like that input impedance. Similarly, try that same switching of the outputs (left/right) and see if the imbalance moves. Finally, just to rule out a synergy (or is it anti-synergy?) between the source and amp at a particular input impedance.
One other thing, do you hear different degrees of imbalance at different attenuation settings?
Best,
Robert
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Just to chime in, i have been struggling with this have encountered the same issue and need to adjust the balance +2 to get the sound from both channels right and centered as one side is louder on my balance unit.
It has been confirmed that on another impedence setting which i have save, it is yet again different and requires a +3.
I have had an issue getting autocal done which i don't know if it is related, it worked previously but keeps hanging, problem is i only have 1 display. I am afraid to touch it as it is as it has not affected my enjoyment from my system and not wanting to do another autocal in fear this my make the problem worst.
One of my impedence settings is even worst, extremely soft on one side.
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Just to chime in, i have been struggling with this have encountered the same issue and need to adjust the balance +2 to get the sound from both channels right and centered as one side is louder on my balance unit.
It has been confirmed that on another impedence setting which i have save, it is yet again different and requires a +3.
I have had an issue getting autocal done which i don't know if it is related, it worked previously but keeps hanging, problem is i only have 1 display. I am afraid to touch it as it is as it has not affected my enjoyment from my system and not wanting to do another autocal in fear this my make the problem worst.
One of my impedence settings is even worst, extremely soft on one side.
These symptoms suggest at least one LDR may be out of spec and not able to calibrate properly. Channel balance shouldn't change noticeably with impedance setting. The calibration algorithm works exactly the same regardless of the impedance setting.
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Have changed out previously all ldrs with new one, same issue.
Seems that my autocal is not completing the whole cycle which i wrote to you before and havent since tried to touch in fear it become unusable meaning no more music and dont want the downtime.
I have not gathered courage to do the firmware update as it means i have to run autocal all over again?
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Have changed out previously all ldrs with new one, same issue.
Seems that my autocal is not completing the whole cycle which i wrote to you before and havent since tried to touch in fear it become unusable meaning no more music and dont want the downtime.
I have not gathered courage to do the firmware update as it means i have to run autocal all over again?
LOL. I never thought updating firmware would require courage! I realize I have a different perspective on this given my familiarity with the inner workings of everything but I literally load/update firmware into our boards on almost a daily basis. It's a highly mature process which just works once you have everything set up.
More recent firmware update work specifically addressed a few lingering issues when using our controller boards in a balanced (master/slave) configuration. For this reason I would encourage updating the firmware on balanced setups especially.
Moreover, running autocal isn't some kind of iffy process that anyone should be afraid of. As long as your LDRs are healthy it just works. If they're not healthy...well, you should find that out and replace them accordingly. Autocal helps in this process. Again, if you have noticeable channel imbalance after changing impedance settings, you definitely need to rerun autocal. My recommendation is - just do it! :thumb:
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Upcoming Changes to Adjustable Impedance in V25 Based Preamps
Appreciate any inputs from users on this topic.
The Problem: The adjustable impedance feature currently allows users to unwittingly select an impedance setting (1 thru 5) and level (1k thru 99k) which has not been properly initialized (has not been through a calibration cycle). This will result in no audio output because the user will have selected an impedance setting/level which has an empty attenuation table. The classic symptom is no audio output or very low audio output that doesn't respond to volume changes. Users get justifiably confused/concerned and wonder why their preamp isn't working. I get emails and phone calls.
The Fix: Firmware update/change which:
a) Will cause the displayed impedance setting/level to blink indicating that the setting/level has not been initialized (has not been run through calibration).
b) Will not allow preamp to switch to a setting/level that is not initialized as evidence by blinking display.
c) Will leave setting #1 fixed @ 20k as the permanent default. User can rerun calibration of this default setting/level at any time but can't change the impedance level of #1.
d) Will revert to default #1 @ 20k, or, to last known valid initialized setting #/level if user makes a change to impedance setting #/level and does not then immediately thereafter initialize this change by running the preamp through a calibration cycle.
To summarize this in as simple language as possible, after this firmware change, when you scroll through impedance settings #2 thru 5, if the display blinks those settings are not initialized and therefore the preamp won't switch to any blinking setting. Setting #1 at 20k will never blink because it's the default and user can't change its level. If you do want to use settings 2 thru 5 or change the level of any of these setting #'s you have to run autocal immediately after selecting/changing them or else they will remain un-initialized.
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Hi Morten,
I'm so glad your back, safe and sound.
Regarding setting impedance setting #1 permanently to 20k, I really hope you can avoid this. I use all five of the available saved settings and 20k isn't even in the ballpark. I'm using the Lampizator Golden Gate DAC. I'm able to fine tune the voicing of the DAC for different recordings by selecting between my various saved impedance settings.
Currently, I have my LDRxB's five impedance settings at 85, 88, 91, 94, 97k. Those are of course per phase on each leg of a balanced input. Even at that, it would be great to have more available saved settings. Now that you have more available memory in your logic system, could you have 10 settings identified as 0 through 9 with 0 being a fixed value?
Best,
Robert
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justubes, if you have the feature where the display goes dark after a period of time, make sure that you disable that (set the delay time to 0) before setting an impedance level. I occasionally forget to do that and run an impedance change. The first time that I did that, I thought the calibration cycle had finished and brought the system back up. Just a thought.
Best,
Robert
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....it would be great to have more available saved settings. Now that you have more available memory in your logic system, could you have 10 settings identified as 0 through 9 with 0 being a fixed value?
Since I'm modifying this code right now anyway expanding from 5 to 10 settings is fairly straightforward. Setting #1 will remain fixed at 20k and the other 2-10 are all adjustable. Once these changes have been tested all new V25 units will shipped with the changes outlined.
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Hi Morten,
It's like you've got a magic wand. More than once, when I've suggested something, it just happens! I did want to reiterate to anyone shopping for a controller that I've come to really value the adjustable input impedance feature. Having lived with three DACs with the LDRxB-V2 (and tried others with it), I would not want to use any other controller that lacked this feature. The Lampizator Golden Gate was especially responsive to different input impedances which I now use to voice the sound for specific recordings. Even a change of a few kohms is audible.
Now, if there were just some way to move/copy an impedance setting from one saved slot number to another to avoid having to do recalibrations to reorder the impedance slots...
Best,
Robert
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Now, if there were just some way to move/copy an impedance setting from one saved slot number to another to avoid having to do recalibrations to reorder the impedance slots...
That's doable but would add a level of additional complexity to the code that would take a fair bit of additional time to implement and test. I simply don't have the time for that right now but will put it on the wish list. :thumb:
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Upcoming Changes to Adjustable Impedance in V25 Based Preamps
I've completed the software mods and will be posting an updated V25 firmware file soon for those interested in uploading this change to their V25 based preamp.
Here's an update on how things turned out.
The Problem: The adjustable impedance feature currently allows users to unwittingly select an impedance setting (1 thru 5) and level (1k thru 99k) which has not been properly initialized (has not been through a calibration cycle). This will result in no audio output because the user will have selected an impedance setting/level which has an empty attenuation table. The classic symptom is no audio output or very low audio output that doesn't respond to volume changes. Users get justifiably confused/concerned and wonder why their preamp isn't working. I get emails and phone calls.
The Fix: Firmware update (rev 1012) as follows:
a) Possible impedance settings has been increased from 5 to 10.
b) Each setting 2 thru 10 can be adjusted by user to be between 1k and 99k.
c) Setting #1 is now fixed at the level of 20k and this level cannot be changed by user.
d) In the event user makes a change to an impedance setting level and forgets to subsequently run autocal to build the attenuation table for that setting/level the preamp will not ignore that setting/level and next time the unit is turned on it will use either the default setting #1/20k or the most recent other valid impedance setting/level if there is one.
e) If the user switches the preamp to an impedance setting/level that has not been initialized (run through autocal) the display will blink and there won't be any audio output.
f) If the user becomes confused, just turn the preamp off and back on again and it will resume operating at the last known valid impedance setting/level.
All preamps shipped on/after Sept 16, 2017 will already incorporate this firmware change.
It's worth noting that the adjustable impedance feature of the V25 is entirely optional. If you never make a change the preamp will use the default setting #1 fixed at 20k input impedance.
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Hi...i am a new user here. As per my knowledge I did reverse the channels to determine if it was a weak channel in my little digital amp but no difference was detected. I did do this with music, not test tones. Is a 6 pts. adjustment significant?Is there a breaking period in which the LDRs' equalize?
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Hi...i am a new user here. As per my knowledge I did reverse the channels to determine if it was a weak channel in my little digital amp but no difference was detected. I did do this with music, not test tones. Is a 6 pts. adjustment significant?Is there a breaking period in which the LDRs' equalize?
Hi Noel,
What model/hardware/firmware version are you working with?
By "6 pts" do you mean you adjusted channel balance by 6 steps to center the balance?
Did you run autocal? If not, please do and note any change.
Best,
Morten
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Hi Morten!
I have been keeping an eye on the Firmware Updates section under the support-section for a while but completely missed out on this thread...
Good news about the rev1012, been looking forward to this!! :D
I'm really eager to update, when do you intend to upload the new firmware or did I miss it somewhere?
Many Thanks!
/ Simon
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Hi Morten!
I have been keeping an eye on the Firmware Updates section under the support-section for a while but completely missed out on this thread...
Good news about the rev1012, been looking forward to this!! :D
I'm really eager to update, when do you intend to upload the new firmware or did I miss it somewhere?
Many Thanks!
/ Simon
I've been letting these changes "mature" a bit since it represents a major update to the adjustable impedance code. It seems to be stable at this point so I'll be updating the firmware/download on the website this week.
The first time your preamp runs with this new version of firmware, it will go through a fairly long reset process that will rewrite/reinitialize all the impedance settings and related attenuation tables. This takes several minutes during which time the master board (in a balanced system) will display numbers as it goes along. When this is done with slave boards in the system there's no status info displayed/available so make sure to just leave the unit alone for 10 minutes after uploading the update to the slave board which is the second board in a balanced system which is usually connected to the lower of the 2 USB ports on the rear panel.
Once both boards are updated, run calibration again for the default setting #1/20k. Setting #1/20k will now be fixed and can no longer be changed. Only settings #2-10 can be changed by the user after this update.
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Morten, are you saying I should run autocal for each 1-10 impedance or can I put in all 9 new impedance and then run autocal?
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Morten, are you saying I should run autocal for each 1-10 impedance or can I put in all 9 new impedance and then run autocal?
Each has to handled separately one at a time. Select a setting #, change the level, press Enter button on remote. Then immediately run Autocal to initialize that new setting/level. Rinse, repeat for other setting # changes.
Changing or setting up a new impedance setting has always required this process. This is not a new procedure.
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I don't see in the v25 instructions on your website where it says to run Autocal after each impedance setting.
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I don't see in the v25 instructions on your website where it says to run Autocal after each impedance setting.
The info is available in the online Product Documentation found via this link: https://www.tortugaaudio.com/support/product-documentation/ (https://www.tortugaaudio.com/support/product-documentation/)
It can be found under General Information -> Preamp Characteristics & Features -> Adjustable Impedance -> How To Set Up Each Impedance Setting
Under this subheading you'll find detailed information on how to set up each impedance setting.
There's a specifically highlighted paragraph which I've copied below that states quite clearly that each setting/level has be set up individually. I need to update this to reflect that the lates V25 firmware now has up to 10 settings but otherwise this generally applies to all models and firmware versions and has not changed materially since adjustable impedance was first introduced.
Changing the impedance level of a given impedance setting number (1-5) must be done for each impedance setting individually per the steps below. For example, this means you have to follow the entire procedure listed below for impedance setting #2 and only #2. Once you’ve completed the procedure for #2, you can then choose to change the impedance for some other impedance setting number. If you wish all 5 settings to be available, you must setup each setting number separately.
The final key step is always to run autocalibration as the final step before initiating or editing another setting #.
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Hi Morten!
I just wanted to say I'm still looking forward to the rev1012 update :D. I hope you find some time to upload it.
Thanks!
/ Simon
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Hi Morten!
I just wanted to say I'm still looking forward to the rev1012 update :D . I hope you find some time to upload it.
Thanks!
/ Simon
It's available now. Rev 1015. Please read the notes before proceeding.
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A new version of the firmware (Rev 1015) is now available for V25 board/preamp users.
This update is only relevant to users who current have version 1011 or older.
This update makes numerous changes to how adjustable impedance is handled.
Info on this update can be found in the online documentation via this link: https://www.tortugaaudio.com/support/product-documentation/ (https://www.tortugaaudio.com/support/product-documentation/)
Go to section: General Information -> Firmware Updates -> V25 Firmware
The details are repeated here:
Release 1012 represents a major change to how adjustable impedance is handled. Upgrading to 1012 will cause your preamp to erase and reset all existing impedance settings and calibration data followed by automatically running calibration at the new fixed default of setting #1 @ 20k. The update will not be completed until this calibration step is completed. Please allow up to 15 minutes to allow the updating, reseting and calibration process to complete. The unit will reboot and restart after completion. Try not to turn of power or otherwise interrupt this process or else it will repeat from the beginning until allowed to fully complete.
** Changes with 1012 **
1) Impedance settings increased from 5 to 10.
2) Impedance setting #1 is now fixed at the default of 20k and can no longer be changed by user. Only settings 2-10 can be setup and modified by user.
3) The display will now blink when user selects an impedance setting number and level combination that has not already been run through calibration.
4) Switching the unit to any setting/level combination that is not calibrated will result in no output from the preamp.
5) Changing an impedance setting/level will not be saved or go into effect until after calibration is run. Press the Enter/Center button on remote after completing a change and then proceed to run calibration as the next step. It's up to the user to ensure calibration is run as the final step. If calibration is not run immediately after making a setting/level change, the unit will revert to last known valid setting/level. If no other settings/levels have been configured the unit will revert to default #1/20k.
6) As before, each setting/level change must be done individually and then processed through calibration to become effective and/or available. User can not make multiple simultaneous changes to settings/levels and run them all through calibration together.
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Thank you Morten!
The Rev 1015 is working very good so far! :D All the 10 impedance settings are working very nicely even though it sometimes hangs in the stage just before the AutoCal starts (where it on my one says 18 on the left display and moves around 0-4 on the right display before it settles), a simple kill the power and restart the AutoCal seems to work ok.
Concerning this improved responsiveness:
" * Tweak - This update improved the responsiveness of the controller to inputs from the Apple Remote and also corrects a minor error in how the preamp responded to repeat commands when user held down the certain buttons on the remote. As a result of this update the controller reacts faster to Apple command especially repeat commands when buttons are held down. Time will tell if the faster response is desirable to end-users or if it proves to be too rapid and may need to be slowed down a tad in a future update. "
I would say it's too rapid now. Somewhere in the middle between how it was before and now would be good. :D
I still got some problems with the remote. By now I have changed to more than 10 different Apple ID numbers and paired the remote again. I'm still having problems/interference with other remotes though. Mostly the repetitive commands. With this newly improved responsiveness, things are getting a bit worse for me since it's mostly raising the volume on my V25s and doing that very fast now and I've got a quite strong power amp... :scratch:
/ Simon
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Thank you Morten!
The Rev 1015 is working very good so far! :D All the 10 impedance settings are working very nicely even though it sometimes hangs in the stage just before the AutoCal starts (where it on my one says 18 on the left display and moves around 0-4 on the right display before it settles), a simple kill the power and restart the AutoCal seems to work ok.
Concerning this improved responsiveness:
" * Tweak - This update improved the responsiveness of the controller to inputs from the Apple Remote and also corrects a minor error in how the preamp responded to repeat commands when user held down the certain buttons on the remote. As a result of this update the controller reacts faster to Apple command especially repeat commands when buttons are held down. Time will tell if the faster response is desirable to end-users or if it proves to be too rapid and may need to be slowed down a tad in a future update. "
I would say it's too rapid now. Somewhere in the middle between how it was before and now would be good. :D
I still got some problems with the remote. By now I have changed to more than 10 different Apple ID numbers and paired the remote again. I'm still having problems/interference with other remotes though. Mostly the repetitive commands. With this newly improved responsiveness, things are getting a bit worse for me since it's mostly raising the volume on my V25s and doing that very fast now and I've got a quite strong power amp... :scratch:
/ Simon
Hi Simon,
I've made some changes to the firmware in version 1016 regarding the Apple auto-repeat speed which I just uploade to the website. More info on it here: http://www.audiocircle.com/index.php?topic=150513.msg1641866#msg1641866 (http://www.audiocircle.com/index.php?topic=150513.msg1641866#msg1641866)
Also, someone posted a link regarding a procedure to better pair up Apple remotes with Apple devices so the Apple device (TV etc. ) doesn't respond to just any Apple remote which is the whole point of the Apple remote having 256 difference IDs. Give this a try is see if it helps. Here's a link to that post: http://www.audiocircle.com/index.php?topic=149567.msg1639080#msg1639080 (http://www.audiocircle.com/index.php?topic=149567.msg1639080#msg1639080)
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Over the past few days I've confirmed that going forward users should always disconnect interconnect cables (input(s) & output) prior to initializing or making subseqent changes to the impedance level associated of the impedance settings (1 through 10). Doing so will ensure reliable results later on when you're switching between impedance levels while listening to music. By not following this procedure you invite the possibiity of there being volume level differences between each impedance setting and/or channel imbalances that shouldn't be there.
I believe the problem stems from having multiple ground connections. When nothing is connected to the preamp, the calibration process has a fixed ground reference that doesn't change regardless of impedance level. However, when multiple interconnects are attached to the preamp there are now multiple ground connection points which may prove to be either soft, noisy, or otherwise susceptible to moving about slightly as impedance levels are changed and clibration is run. As a result of these multiple ground connections, the results of the calibration process may not be consistent.
To be clear, you may not run into this problem with your preamp and system. But you can and some people have. I've been able to reproduce the problem here in our shop.
Again, the simple fix is to detach your interconnects while setting up/changing your impedance levels and running calibration for each level. Once this is done, reconnect your interconnects and run the preamp normally including being able to hot switch between preamp settings to optimize your impedance setting for your rig.
Adjustable impedance is unique tool available to Tortuga Audio preamp owners. While it can be useful to optimize performance the setup process can be a bit complex and tedious. And for most users there's no compelling need to even mess with adjustable impedance unless you're curious. But if you do, please be mindful of the above and proceed deliberately.
Cheers,
Morten
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Over the past few days I've confirmed that going forward users should always disconnect interconnect cables (input(s) & output) prior to initializing or making subseqent changes to the impedance level associated of the impedance settings (1 through 10). Doing so will ensure reliable results later on when you're switching between impedance levels while listening to music. By not following this procedure you invite the possibiity of there being volume level differences between each impedance setting and/or channel imbalances that shouldn't be there.
I believe the problem stems from having multiple ground connections. When nothing is connected to the preamp, the calibration process has a fixed ground reference that doesn't change regardless of impedance level. However, when multiple interconnects are attached to the preamp there are now multiple ground connection points which may prove to be either soft, noisy, or otherwise susceptible to moving about slightly as impedance levels are changed and clibration is run. As a result of these multiple ground connections, the results of the calibration process may not be consistent.
To be clear, you may not run into this problem with your preamp and system. But you can and some people have. I've been able to reproduce the problem here in our shop.
Again, the simple fix is to detach your interconnects while setting up/changing your impedance levels and running calibration for each level. Once this is done, reconnect your interconnects and run the preamp normally including being able to hot switch between preamp settings to optimize your impedance setting for your rig.
Adjustable impedance is unique tool available to Tortuga Audio preamp owners. While it can be useful to optimize performance the setup process can be a bit complex and tedious. And for most users there's no compelling need to even mess with adjustable impedance unless you're curious. But if you do, please be mindful of the above and proceed deliberately.
Cheers,
Morten
Very interesting Morten, thank you!
Would there be any benefit to disconnecting all interconnects for a normal auto calibration not involving impedance changes?
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Very interesting Morten, thank you!
Would there be any benefit to disconnecting all interconnects for a normal auto calibration not involving impedance changes?
I don't think so. For a given impedance setting/level you should be able to run calibration with everything connected normally as that will likely remain the "normal". This has been the case for most users most of the time and in my own rig I've never had an issue with this. It's when you go setting up multiple impedance settings/levels each requiring you run calibration that it's important to do so with interconnects disconnected.
FYI, the successor to the V25 board will have ground isolation for each input and the control system will have its own isolated ground plane so that calibration will always independent of externally connected grounds.
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Would a viable alternative be to unplug all components from AC except the the Tortuga? This might be easier in some setups.
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Would a viable alternative be to unplug all components from AC except the the Tortuga? This might be easier in some setups.
In theory that should be comparable.
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hello,
i have ldr balanced since 2015. v2.1
the firmware is the last version
I always had small problems of balance left right.
the auto calibration is ok !
I am looking for a procedure, and a diagram for the modules with precision resistances for pré calibration.
i have one display for two balanced ldr modules.
thanks for you help
christophe.
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hello,
i have ldr balanced since 2015. v2.1
the firmware is the last version
I always had small problems of balance left right.
the auto calibration is ok !
I am looking for a procedure, and a diagram for the modules with precision resistances for pré calibration.
i have one display for two balanced ldr modules.
thanks for you help
christophe.
Hi Christophe,
We reluctantly documented a simplified description of precalibration for the V2/V2.1. I say reluctantly because there's great opportunity to screw things up doing precalibration. For those unfamiliar with the term precalibration (or "precal") it's a way to normalize the hardware so that it can accurately measure resistance during LDR calibration (or "cal" as distinct from precal). This is normally only done once during the initial commissioning of the board.
During precal, each of the 4 LDRs are removed and a fixed resistor value is plugged in. Two resistor values are required - 100 ohm and 100k ohm. Each LDR (#1 through #4) sees 100R and then sees 100k before switching to the next LDR. Thus it takes 8 steps (2 per LDR). Although each LDR plugs into a 2x2 pin header, only the 2 pins facing the rear of the board (away from the black processor chip) are involved in precalibration. The 100R and 100K resistors must be temporarily connected across those 2 rear pins.
This procedure is described in more detail in our online product documentation here: https://www.tortugaaudio.com/documents/product-documentation-general/?section=v2-apple-control-schemes (https://www.tortugaaudio.com/documents/product-documentation-general/?section=v2-apple-control-schemes)
Info on how to identify which LDR is which can be found here: https://www.tortugaaudio.com/documents/product-documentation-general/?section=ldr-replacement-instructions (https://www.tortugaaudio.com/documents/product-documentation-general/?section=ldr-replacement-instructions)
Now, in order for the user to have any chance of executing precalibration successfully you will need to have dual 7 segment displays connected to each V2/V2.1 board. A single display module will not show enough info to know what's going on - I'd never attempt to do this with only 1 display module. Each board has to be done separately. If you have dual boards in a balanced configuration, you have to disconnect them and do each of them by itself.
Good luck,
Morten
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I have two DACs, which are expected to be connected through XLR inputs (in a balanced configuration). Do I have to disconnect them separately and calibrate each of them for impedance matching?
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I have two DACs, which are expected to be connected through XLR inputs (in a balanced configuration). Do I have to disconnect them separately and calibrate each of them for impedance matching?
Let me preface my answer by noting that adjustable impedance is NOT a precise deterministic way to achieve impedance matching. Adjustable impedance is a mechanism that allows the user to explore the possibility of finding an optimal impedance setting for their particular system. In most cases, increasing the preamp's input impedance beyond the default 20k will not result in any discernable changes in sound quality. But in some cases it will. And sometimes even lowering the impedance below 20k may yield improvements. You can't know in advance. The only general guidance is to have the preamp's input impedance be set equal to the amplifier's input impedance such that the effective combined parallel impedance equals 50% of their nominal impedance (example: preamp - 50k, amp - 50k, effective impedance = (50*50)/(50+50) = 25k. )
In fact, it's technically a misnomer to use the phrase "impedance matching" at all. Contemporary consumer audio does not really use "impedance matching" as such. For example, the output impedance of a DAC does not try to match the input impedance of a preamp, and the output impedance of a preamp does not try to match the input impedance of an amplifier. They could, if they did, but they don't. Instead, we use the concept of "impedance bridging" where the output impedance of the source component is relative low compared to the much higher input impedance of the downstream component to which it's attached. Thus, a DAC may typically have an output impedance of say 100 ohms, connected to a preamp with an input impedance of say 20,000 ohms resulting in an impedance bridging ratio of 20,000/100 = 200:1. The simple idea behind this is to make it easy for the signal to exit the upstream component while limiting the load (current demand placed on upstream source component) presented by the connected downstream component. With conventional active components, the traditional guidance is to achieve a minimum bridging ratio of 10:1 to ensure good performance. In the case of passive preamps, you'll often see this guidance raised to 50:1 although that high a ratio is often not required depending on how robust the output stage of the upstream component delivering the signal.
To answer your question directly, no, you do not need to calibrate based on what component is connected or selected. In fact, during the the LDR calibration process, all inputs and outputs are temporarily automatically disconnected within the preamp controller. Therefore, you normally don't have to disconnect any cables.
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It’s really wonderful for a passive preamp to reach such a high level of sophistication and flexibility. It’s already a breeze to achieve "impedance bridging". Moreover, the software-driven calibration process will theoretically become more and more intelligent.
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It’s really wonderful for a passive preamp to reach such a high level of sophistication and flexibility. It’s already a breeze to achieve "impedance bridging". Moreover, the software-driven calibration process will theoretically become more and more intelligent.
I have just found that my power amp (Creek Evolution 100A) is actually not paticularly passive preamp-friendly as its balanced line-level input impedance is a uniform 42k ohms across the audioband, while the unbalanced input impedance is only 10.9k ohms.
But even so, an impedance ratio of 100:1 or greater (amp input : source output) is almost certain to work well with passive preamps as noted in your technical document. Here the output impedance of a DAC becomes critical. The output impedance of my Holo Audio Spring 3 DAC is 27 ohms at RCA and 54 ohms at XLR. The output impedance of my other DAC (Gustard A22) at both RCA and XLR is 100 ohms.
Hopefully I have figured out my gear matching correctly.
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I have just found that my power amp (Creek Evolution 100A) is actually not paticularly passive preamp-friendly as its balanced line-level input impedance is a uniform 42k ohms across the audioband, while the unbalanced input impedance is only 10.9k ohms.
But even so, an impedance ratio of 100:1 or greater (amp input : source output) is almost certain to work well with passive preamps as noted in your technical document. Here the output impedance of a DAC becomes critical. The output impedance of my Holo Audio Spring 3 DAC is 27 ohms at RCA and 54 ohms at XLR. The output impedance of my other DAC (Gustard A22) at both RCA and XLR is 100 ohms.
Hopefully I have figured out my gear matching correctly.
Since your preamp is balanced, I see no problem here. The 100:1 impedance ratio is ONLY guidance and does not determine outcome. I've come around to the view that impedance ratio's with passive preamps is NOT the primary metric for whether a passive will fit well within a system. The primary factor is the ability of your source component(s) to deliver the audio energy. This depends on how robust the output stage is in your source components. Strong/robust current output drive matters more than some impedance ratio. That is not something you can know from specifications. With active preamps an impedance ratio of 10:1 is considered adequate. With passive preamps, 50:1 or greater usually works well but you can get really excellent performance with much lower ratios.
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Thank you. Is it necessary for me to add an external headphone amp without a volume control? There is still an XLR output left unused on my LDR3000x.V3 Passive, which is balanced only (3 in | 2 out | XLR). My K240 MKII headphones have a rated impedance of 55 ohms.
My desktop Creek 100A integrated amp uses a dedicated headphone amplifier to provide a low impedance output signal to the jack socket on the front panel. This is supplied by its active pre-amp and therefore, if I select AV Direct for Line input, the signal will bypass the pre-amp and pass directly through to the power amp, so theoretically no signal will be available to the headphones.
But actually this has not been the case. I own a Creek OBH-22 passive preamplifier that seems to work fine with my K240 MKII headphones through the use of the passive pre-amp’s volume control. Moreover, a headphone amp without a volume control is a pretty rare beast unless you custom build it.
A quick Google search says "Pairing a headphone with an impedance of 2.5-8 times higher than the source impedance should yield good results. This recommended ratio is commonly known as the ‘rule of eighths’ and contributes to proper driver control (damping factor). Pairing a headphone with an equal or lower impedance than the source will likely result in unpredictable (poor) sound quality."
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Thank you. Is it necessary for me to add an external headphone amp without a volume control? There is still an XLR output left unused on my LDR3000x.V3 Passive, which is balanced only (3 in | 2 out | XLR). My K240 MKII headphones have a rated impedance of 55 ohms.
My desktop Creek 100A integrated amp uses a dedicated headphone amplifier to provide a low impedance output signal to the jack socket on the front panel. This is supplied by its active pre-amp and therefore, if I select AV Direct for Line input, the signal will bypass the pre-amp and pass directly through to the power amp, so theoretically no signal will be available to the headphones.
I can't think of any show stopper reason why you couldn't use your Creek amp in AV bypass mode and rely on the LDR3000x.V3 preamp for volume control.
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Thanks. That's very reassuring.