Volume control systems in preamps

plasmod3

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Aug 28, 2020
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Hi Everyone,

I am wondering what is the best volume control mechanism we have out there for preamps?

TVC or transformer volume control seems to have an advantage over a resistor or pot setup, are there other more esoteric ways of the volume stage in a pre amp that imparts good qualities to the sound?

What about valve gain control as a way of volume control - pros and cons of this approach over the above?

Thanks in advance
 
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plasmod3

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Agree folsom pots not the way to go although zanden makes a good preamp with the pots - how did they achieve it there i wonder? Any thoughts on TVC or VGC?
 

jfrech

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Folsom

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Pots can sound ok if designed around them, but never fabulous. Higher voltages running through them seems to help some (certain tube designs).
 

analogsa

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My view is that tvc/avc are great as standalone passive units. In the presence of active buffering or amplification their advantages are less clear.

My choice for analogue would still be a silver mechanical switch with good resistors, perhaps z-foils and for digital...yes, a digital attenuator, followed by a good buffer/amplification stage.

It is a lot easier to point at what makes a poor sounding attenuator: r-2r relays or cmos switches based attenuators and anything chip based, whether on expensive Japanese or on $2 chips. The high end is full of such examples.
 

plasmod3

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Thanks guys will look up more on the tvc and avc, not very familiar with buffering as well look like another good lead to look into to understand more
 

Mikem53

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I have a Django TVC based on the Stevens & Billington (S&B) TX 102 MKII Volume Control Transformers. I think they sound awesome and used them for years, they also can produce gain. Also had some nude attenuators that hung off the amps input.. One resistor for each step, about 15, I believe.. not very convenient, or as good as the TVC, but about as minimalistic as they come. I currently have a stepped relay switched attenuation that claims perfect channel matching and unmeasurable distortion... Sounds pretty good and currently prefer the active tube gain stage vs passive.. good luck..
 

kernelbob

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Audition one of the Tortuga units. These are available in active or passive products, single ended, balanced, and combo implementations. I'm using a balanced LDRxB purely passive controller in a biamped system. It feeds a pair of monoblock tube amps (100 kohm input impedance per phase) on top and a pair of monoblock solid state amps (25 kohms input impedance). I've put a Tortuga tube buffer ahead of the bass amps with 100 kohms input impedance per phase.

With a passive unit, impedance management is inportant. The Tortuga tube buffer or the active tube/vfet preamp variant solves the challenge of driving very low input impedance amps.

The key to the Tortuga products is that there are no physical switches, potentiometers, or resistor attenuator arrays in the signal path. Even input selection, stereo/mono, and absolute phase selection is handled without any physical switches. Loads of features such as user defined input impedance control using the remote (I have nine settings between 90 and 99 kohms defined with 97 the one that my Lampizator Pacific DAC likes best).

Robert
 
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lordcloud

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I have Tortuga Balanced preamp that I think sounds amazing and is very transparent. I recommend it as well as TVC preamps.

I had a TVC preamp before the Tortuga, and if I could find a Stereoknight balanced TVC, I would likely own it as well.

Both types are highly recommended, if it want a preamp that's more about transparency and less about a type of sound.

I'll likely end up getting a Benchmark LA4 in the end though.
 

plasmod3

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thanks guys - a tortuga & TVC- these are new brands for me and will certainly look into it. The absence of physical switches here is quite intereesting Bob & lordcloud- many thanks for bringing my attention to this one. I looked at the bespoke company's preamps as quite a few members have had good experiences with it - they havent been replying to emails though .

What are everyone's thoughts on a passive vs an active preamp?take for eg the ypsilon preamps - the active is much much more expensive than the passive - john atkinson in stereophile seems more concerned on the active stages though. I imagine the more you add to a circuit the more likely for one to generate a 'flavour'
 
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lordcloud

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thanks guys - a tortuga & TVC- these are new brands for me and will certainly look into it. The absence of physical switches here is quite intereesting Bob & lordcloud- many thanks for bringing my attention to this one. I looked at the bespoke company's preamps as quite a few members have had good experiences with it - they havent been replying to emails though .

What are everyone's thoughts on a passive vs an active preamp?take for eg the ypsilon preamps - the active is much much more expensive than the passive - john atkinson in stereophile seems more concerned on the active stages though. I imagine the more you add to a circuit the more likely for one to generate a 'flavour'

I believe that active preamps can be very transparent (Benchmark LA4), however most are, just like the vast majority of all audio components, designed to sound "good". Good being very subjective and determined by the designer and purchaser.

Passive preamps are usually more transparent, or at least designed less with a sound in mind, and more with transparency as the end goal.

In my experience, almost all audiophiles care about components sounding good, not recordings sounding good. So they go for the more colored component, ie, active preamps.

There's also system matching. I think most components are designed to need an active preamp, otherwise you miss out on dynamics and other things.
 
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Mike Lavigne

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if we consider the finest possible volume control implementation available i think the 'optical coupler's used on the darTZeel NHB-18NS preamp are a strong consideration.

there is no potentiometer or resistor network in line with the audio, volume control being by passive attenuation governed by a dedicated processor via analogue optical couplers, offering 192 steps in increments of 0.5dB.
 

kernelbob

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Oct 23, 2011
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if we consider the finest possible volume control implementation available i think the 'optical coupler's used on the darTZeel NHB-18NS preamp are a strong consideration.
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.
 

kernelbob

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Oct 23, 2011
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thanks guys - a tortuga & TVC- these are new brands for me and will certainly look into it. The absence of physical switches here is quite intereesting Bob & lordcloud- many thanks for bringing my attention to this one. I looked at the bespoke company's preamps as quite a few members have had good experiences with it - they havent been replying to emails though .

What are everyone's thoughts on a passive vs an active preamp?take for eg the ypsilon preamps - the active is much much more expensive than the passive - john atkinson in stereophile seems more concerned on the active stages though. I imagine the more you add to a circuit the more likely for one to generate a 'flavour'
Regarding your statement "I imagine the more you add to a circuit the more likely for one to generate a 'flavour' ", my experience with the Tortuga was exactly that each instrument in an orchestra had a more realistic and unique sound. Coherence of individual instruments was also more obvious as well as resolution of instruments in the soundstage.
 
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microstrip

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if we consider the finest possible volume control implementation available i think the 'optical coupler's used on the darTZeel NHB-18NS preamp are a strong consideration.

Mike,

Although it can sound great, technically it is far from perfection. All these optical devices have more noise and distortion than an high quality resistor with a top switch - probably it is why we like their sound. We do not pay a lot for an active preamplifier to get a "transparent" device! :) Totugaaudio, for example, are very clear on this aspect.

BTW, most of the high-end technical descriptions flowing around are vague and even misleading - usually there is not information enough be technically analyzed.
 

bazelio

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Count me in the group that feels optical devices really have no purpose nor place in an audio device. Whomever said it earlier in the thread was right (paraphrasing): if you're buffering after the volume control, then a high precision resistor ladder is fine. There's no need for nor any advantage from autoformers, transformers, and certainly not LDRs in those cases.
 

bonzo75

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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.
 

plasmod3

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amazing insights here guys. I am not sure if i am flash on opto components as well. am wondering with the fm acoustics pre amps - what sort of attenuators do they use?
 

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