[TheMonkey]

Thank you Morten!

The Rev 1015 is working very good so far!    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. 

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... 

/ Simon

[tortugaranger]

Thank you Morten!

The Rev 1015 is working very good so far!    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. 

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... 

/ 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

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

[tortugaranger]

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

[33na3rd]

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?

[tortugaranger]

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.

[konut]

Would a viable alternative be to unplug all components from AC except the the Tortuga? This might be easier in some setups.

[tortugaranger]

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.

[germamiga]

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.

[tortugaranger]

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

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

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

[xieqiao]

 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? 

[tortugaranger]

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.

[xieqiao]

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.

[xieqiao]

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.

[tortugaranger]

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.

[xieqiao]

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."

[tortugaranger]

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.

[xieqiao]

Thanks. That's very reassuring.