Adjustable Impedance

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tortugaranger

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Re: Adjustable Impedance
« Reply #20 on: 23 Apr 2015, 12:00 pm »
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.

justubes

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Re: Adjustable Impedance
« Reply #21 on: 25 Apr 2015, 06:42 pm »
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.

tortugaranger

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Re: Adjustable Impedance
« Reply #22 on: 25 Apr 2015, 07:49 pm »
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.



craig sawyers

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Re: Adjustable Impedance
« Reply #23 on: 28 Apr 2015, 09:28 am »
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

JohnR

Re: Adjustable Impedance
« Reply #24 on: 28 Apr 2015, 10:59 am »
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.

tortugaranger

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Re: Adjustable Impedance
« Reply #25 on: 28 Apr 2015, 06:20 pm »
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.

tortugaranger

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Re: Adjustable Impedance
« Reply #26 on: 28 Apr 2015, 06:28 pm »
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) 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

JohnR

Re: Adjustable Impedance
« Reply #27 on: 29 Apr 2015, 05:32 pm »
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... :)

tortugaranger

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Re: Adjustable Impedance
« Reply #28 on: 29 Apr 2015, 07:55 pm »
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!

tortugaranger

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Re: Adjustable Impedance
« Reply #29 on: 21 May 2015, 05:09 pm »
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

tortugaranger

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Re: Adjustable Impedance
« Reply #30 on: 5 Jun 2015, 02:49 pm »
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:

CSI

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Re: Adjustable Impedance
« Reply #31 on: 5 Jun 2015, 03:35 pm »
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.

tortugaranger

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Re: Adjustable Impedance
« Reply #32 on: 5 Jun 2015, 03:51 pm »
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:

Norbert2nd

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Re: Adjustable Impedance
« Reply #33 on: 10 Sep 2015, 10:21 am »
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

tortugaranger

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Re: Adjustable Impedance
« Reply #34 on: 10 Sep 2015, 02:16 pm »
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:

kernelbob

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Re: Adjustable Impedance
« Reply #35 on: 10 Sep 2015, 02:26 pm »
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

Norbert2nd

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Re: Adjustable Impedance
« Reply #36 on: 11 Sep 2015, 10:39 am »
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

tortugaranger

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Re: Adjustable Impedance
« Reply #37 on: 11 Sep 2015, 02:49 pm »
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.

doggie

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Re: Adjustable Impedance
« Reply #38 on: 17 Feb 2016, 06:57 pm »
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.

tortugaranger

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Re: Adjustable Impedance
« Reply #39 on: 19 Feb 2016, 03:52 pm »
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
« Last Edit: 19 Feb 2016, 10:12 pm by tortugaranger »