Volume control systems in preamps

Folsom

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Oct 26, 2015
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I don’t see the need to apply philosophy. If you like the sound, use it.
 

Blue58

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Jan 20, 2013
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I’ve been very happy for 3 years with my Java Triple Shot from Java HiFi in New Zealand. So much so I placed an order for their new version way back in February but due to the pandemic production has been slow and I expect it in 2021. It uses optocouplers btw.

The only other device I’d consider is, as has been mentioned, Silver Slagle Autoformers from Emia. Not a fan of TVCs.
 

bazelio

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Sep 27, 2016
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Thomas mayer and JC Morrison (Silbatone) use Slagle silver AVC for their active preamps, and Joe Roberts said they tried everything and ended up with the slagle silver.
Slagle also has the silver AVC in his (and Jeffrey Jackson's) Emia DHT preamp. But then, it makes sense as they give the user a switch to operate it in either active or pure passive modes. I'm going to demo this at some point.

Link: http://myemia.com/Linestage.html
 
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lordcloud

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I don't disagree that there is obviously distortion and noise in the LDR implementations, as even Tortuga points out. And I do prefer the Benchmark LA4 for noise free and free sound (even though I never thought I would go back to an active preamp).

However, the Tortuga is still more transparent sounding than almost every preamp I've heard. I'm not sure why that is.
 

LL21

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Dec 26, 2010
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The term "optical couplers" referenced in the darTZeel preamps sounds like these might also be LDR devices (light dependent resistors) which is the technology used in by Tortuga. The top tier of the Constellation preamps also used LDRs, at least the version from several years ago. Regarding the Tortuga implementation, no physical switches, potentiometers, etc. are used anywhere in the signal path.
Yes, I have read that about Constellation as well...someone said they stopped using them in their later reference series? Something about the volume needing to power up or down or something due to the way the light dependent resistors work? So there was a delay or something?
 

kernelbob

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Oct 23, 2011
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Yes, I have read that about Constellation as well...someone said they stopped using them in their later reference series? Something about the volume needing to power up or down or something due to the way the light dependent resistors work? So there was a delay or something?
At very high attenuation levels, meaning a large amount of attenuation, the LDRs do exhibit higher harmonic distortion. I never use that amount of attenuation.

I'm reporting on my experience, not on generalizations. When I've taken my Tortuga to other's systems, including at audio shows for after hours private comparisons, it consistently trounced preamps consting five figures and up. So it isn't just my experience with my system.
 

LL21

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At very high attenuation levels, meaning a large amount of attenuation, the LDRs do exhibit higher harmonic distortion. I never use that amount of attenuation.

I'm reporting on my experience, not on generalizations. When I've taken my Tortuga to other's systems, including at audio shows for after hours private comparisons, it consistently trounced preamps consting five figures and up. So it isn't just my experience with my system.
Great stuff...just looked them up. Do you use the passive or active version?
 

plasmod3

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Aug 28, 2020
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i am admitting quite a bit of curiosity here.... see what you guys think re my rational ....a resister by nature has to be something that does not conduct electricity well - hence a 'resistance' . that being the case it wouldn't be of a copper or silver nature and will by it's resistance nature - introduce distortion/noise as such. LDR is still a resistor , just light dependent in which case the metal used is not silver or copper. Herein the dichotomy, do you spend all that money on ofc cables and silverwiring in your cables then put it through a resister that is anything but which will introduce distortion and interference? It's like that fuse you installed - it made a difference be it be an sr or a beeswax fuse but that small piece of wire made a difference and many found it to be a good change. That being the case wont it be a great idea to move away from all resistance based attenuators? One would have thought that is in audiophily almost a given direction? Resistors are generally cheap unless build like one of the koda attenuators where the cost is evident; having said that the code of a koda attenuator is in the workmanship not the cost of its parts.
 

kernelbob

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Oct 23, 2011
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i am admitting quite a bit of curiosity here.... see what you guys think re my rational ....a resister by nature has to be something that does not conduct electricity well - hence a 'resistance' . that being the case it wouldn't be of a copper or silver nature and will by it's resistance nature - introduce distortion/noise as such. LDR is still a resistor , just light dependent in which case the metal used is not silver or copper. Herein the dichotomy, do you spend all that money on ofc cables and silverwiring in your cables then put it through a resister that is anything but which will introduce distortion and interference? It's like that fuse you installed - it made a difference be it be an sr or a beeswax fuse but that small piece of wire made a difference and many found it to be a good change. That being the case wont it be a great idea to move away from all resistance based attenuators? One would have thought that is in audiophily almost a given direction? Resistors are generally cheap unless build like one of the koda attenuators where the cost is evident; having said that the code of a koda attenuator is in the workmanship not the cost of its parts.
The key point with the LDR is that there is no switching contact surface that the signal has to traverse. A magnified image of the wiper of a potentiometer or the contact point is relatively rough. The signal has to jump across this. So, even though a TVC can eliminate the contact surface of the volume control, the best attenuator doesn't address the various switches in the signal path (such as input source switching, channel balance, phase inversion (if you have that capability), input impedance selection (also if you have that). The bottom line is that the only contact to contact points in the Tortuga are the connecctions from the input cable and to the output cable. You can periodically clean and treat these external connections as you choose.

In terms of impact on the integrity of the signal, the higher the signal voltage (i.e. volume), the easier it is for the signal to cross those physical boundaries. However, the converse is also true. For low level signal information, the boundaries become more significant and this is where nuances of the signal are more impacted. It is these subtleties where the Tortuga shines with a striking coherence of instrumental timbre and spatial coherence.
 

kernelbob

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Oct 23, 2011
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Great stuff...just looked them up. Do you use the passive or active version?
I use the passive LDRxB. It uses fully balanced input and output. It has one set of single ended inputs and outputs, but I don't use them. The power supply is 12V using a wall wort. Morten offers a separate battery power supply. I've set up my own battery supply (simple to do) using a large 12V Optima deep cycle marine battery and the smallest automatic trickle charger to automatically keep it topped off. The only home grown part was to wire a connection from the battery terminals to the LDRxB power input. By the way, I've never heard any difference of the trickle charger charging or not (no hum, no noise, etc.).

I ordered the optional absolute phase inversion option. This lets me switch absolute phase of the system from listening position using the remote. This is done without instroducing any additional LDRs in the signal path and of course without introducing physical switches either. This is an option that I would now not be without. Easily audible and needs to be set properly for each recording.
 

kernelbob

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Oct 23, 2011
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Yes, I have read that about Constellation as well...someone said they stopped using them in their later reference series? Something about the volume needing to power up or down or something due to the way the light dependent resistors work? So there was a delay or something?
I'm not clear what you're describing regarding "volume needing to power up or down...". A characteristic of LDRs is that their resistance for a given input LED intensity can vary over a long time frame. I know some owners of other brands that use LDRs complaining about this.

Tortuga doesn't have a problem with that. All control functions are via software. For instance, if you press "volume up or down", "change input from 1 to 2", "change the input impedance from one value to another", etc., your remote sends the command to the Tortuga. The software determines what LDR changes are needed, and makes the necessary changes to the various LED levels of the relevant LDRs.

Input impedance is set at the factory at 20 kohms. The user can define up to nine custom input impedances from 1k to 99k (per phase if using a balanced signal). Each custom selection can be implemented in about 5 minutes by clicking the "calibrate" command from the "impedance" menu. At any time you can command to recalibrate an existing impedance setting by clicking that commend.

The calibration generates a lookup table for that input impedance setting with each entry in that table corresponding to the voltage of each LDR's LED for a specific volume level. Each step is 0.6 dB. This calibration process ensures that there is no L/R imbalance and that each volume level is correct for the setting, and that the input impedance is as specified by the user.

I suspect the Constellation LDR attenuation mechanism did not have that customer controlled calibration capability. By the way, I can't remember the last time I've recalibrated mine other than deciding to change one/some of the nine custom input impedance values. I only need to redefine any of my custom impedances when I try a different output tube type in my Pacific DAC. Each tube type seems to have its own favorite input impedance. Subtle? Yes, but audible.
 

LL21

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Dec 26, 2010
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I'm not clear what you're describing regarding "volume needing to power up or down...". A characteristic of LDRs is that their resistance for a given input LED intensity can vary over a long time frame. I know some owners of other brands that use LDRs complaining about this.

Tortuga doesn't have a problem with that. All control functions are via software. For instance, if you press "volume up or down", "change input from 1 to 2", "change the input impedance from one value to another", etc., your remote sends the command to the Tortuga. The software determines what LDR changes are needed, and makes the necessary changes to the various LED levels of the relevant LDRs..."
Hi...thank you. Sorry...did not mean to set hares running...i was simply [poorly] remembering a comment a reviewer made. I went back to find it. Here it is from Robert Harley when reviewing the Constellation Altair 2 Ref preamplifier:

"Inside, the Altair’ [2]s volume control is now a monolithic stepped-attenuator under digital control rather than the elaborate light-dependent-resistor circuit of the original [Altair 1 Reference Preamp]. The light-dependent-resistor volume control took a long time to stabilize and sound its best, leading to the decision to implement the new attenuator..."


I am not sure what that means...and certainly had no intention of decrying anyone's tech out there...i had honestly never heard of LDR until I read this review on the Altair 2 which I was curious to know about having heard great things about it when i was considering a reference preamp to replace the CJ GAT 2.
 

kernelbob

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Oct 23, 2011
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Hi...thank you. Sorry...did not mean to set hares running...i was simply [poorly] remembering a comment a reviewer made. I went back to find it. Here it is from Robert Harley when reviewing the Constellation Altair 2 Ref preamplifier:

"Inside, the Altair’ [2]s volume control is now a monolithic stepped-attenuator under digital control rather than the elaborate light-dependent-resistor circuit of the original [Altair 1 Reference Preamp]. The light-dependent-resistor volume control took a long time to stabilize and sound its best, leading to the decision to implement the new attenuator..."


I am not sure what that means...and certainly had no intention of decrying anyone's tech out there...i had honestly never heard of LDR until I read this review on the Altair 2 which I was curious to know about having heard great things about it when i was considering a reference preamp to replace the CJ GAT 2.
When changing attenuation settings in my LDRxB, there is absolutely no stabilization delay. In fact, this is the first time I've heard of this in any vendor's LDR based attenuator. I've heard complaints of long term level drift from owners of other LDR controllers. In those products, the solution is to send the unit back to the factory for service.

Tortuga uses LDRs with an integrated LED in sealed modules and uses their own software system to manage all aspects of their preamps/controllers. If any LDR drift occurs, one click of the remote recalibrates them. Worse case, if an LDR unit needs to be replaced, the plug in module can be replaced by the user.

When they chose to use LDRs, Constellation only used them in their top end preamp ($200,000), relegating their lower price point preamp to other conventional attenuators. At the time, they made it clear that the LDR approach was used in their top-end unit for sonic superiority.

Don't be fooled by the price (mine was under $3k). This is a top-end unit in every way. When I first auditioned a Tortuga (the balanced LDR1B with only one input), it absolutely trounced my then current preamp, the ARC REF3 with much better soundstage, purity, instrumental resolution, dynamics, bass (yes great bass from a passive controller).

Apologies for the long replies, but the Tortuga is a giant killer at a bargain price.

Best, Robert
 
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LL21

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Fantastic information! Yes, I recall the background on Constellation is that it was conceived as a pantheon of great audio designers, coming together, privately funded to think blue sky about the absolute best, no-limits audio designs...and then commercially producing them. So I can imagine if they used this LDR design, that is a tremendous endorsement and entirely supportive of your giant killer description! $200K preamp!
 

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