Nothing is best

June 18, 2017
 by Paul McGowan

I’m not sure how this thread morphed into a How I built this about volume controls but things have a tendency to just drift in a certain direction. But, I ramble on.

In yesterday’s post, I told the story of boiling the innards of a volume control down to nothing more than a single high-quality resistor. It was the best we’d heard but it still had a signature that wasn’t appreciated. How could it get better than a single, simple, component? By eliminating even that one device.

Preamplifiers are impractical designs. They consist of three things: input switches, volume control, output amplifier. With the volume control turned on high so no attenuation happens, preamps put out far more signal than needed to clip an amplifier. Which means volume control always attenuate—reduce signal level—to match the gain of the output amplifier. Seems rather counter-intuitive. We are forced to throw away signal to compensate for the amplifier’s gain.

Then, a light bulb went off in my head. Why suffer the added distortion of a volume control when it could be eliminated entirely by changing the output stage gain. Thus, a variable gain preamplifier is reduced from the tradition of three parts to two: input switching, variable gain output stage.

The first iteration of this technology we called the Gain Cell, which appeared nearly a decade ago in the GC Series. Today, it’s what is also inside the Stellar Gain Cell DAC/Preamp. But, we didn’t stop there. Bascom H. King (BHK) realized the same thing. Volume controls are the Achille’s heel of preamplifiers and, using entirely different techniques, he too varies the vacuum tube gain of the BHK Signature preamplifier in place of a traditional volume control.

Both preamp offerings of the company are based upon the perfect volume control. No volume control.

And that is how you make a better volume control.

Nothing is best.

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20 comments on “Nothing is best”

  1. A bold final statement, Paul. Having an old PS Audio GCPH phono preamp in my stereo system I was convinced that the solution used in the DS-DAC was even better. However this might be valid for digital sources only? Why not designing a power amp with digital inputs only having a bit-perfect digital connection to any digital source? For vinyl aficionados a PS Audio GCPH MK II could be added offering a fine AD-converter and a near perfect RIAA equalisation (for different record label specific schemes) and near perfect subsonic filter on a digital base??? Oh, I forgot, you are not a vinyl lover. What a pity.

    1. If you are a vinyl lover, and it is your main source, the last thing most of us would want is to digitize a pure analog chain. I very much doubt it would be a big seller. The current phono preamp has an ADC, and I2S that can be run into the Directstream. So you would just be doing the analog conversion before the amp. I believe some do that, but it hasn’t turned into the preferred signal path.
      My dream speakers are Legacy Aeris, and the only thing I have found hard to accept is the AD/DA crossover that includes room correction, and equalization. Everyone who owns them and all the reviews are positive, so I’ve come to accept that it works.
      Us older guys, and for all I know you may be one too, just more advanced than many of us that still are wary of added conversions.
      But I wonder if Ted has ever tried building an ADC using FPGAs? That might be a real advance in ADCs.

      1. Indeed, it is always a matter of optima the signal pass characterized by inherently added degradations of the original signal (coloration, distortions). But if today in most cases the analog original is already recorded in a digital Format I assume that AD-conversion is near perfect today. Thus why not using all advantagages of digital signal processing having today most powerful processors (compared to the processor performance 30 years ago) and keeping the path pure digital to the power amp input? I cannot see a similar progress in the design of resistors, capacitors, transformers or analog amp circuits as in digital signal processing.

    2. Exactly. In the end, we need an analog based volume control solution so vinyl can be accommodated. That’s why we designed Stellar to be analog based, as well as BHK. If no one was interested in vinyl the story would be quite different.

  2. Choice , the BK preamp has more then one stage ,this in itself removes a bit of sonic purity
    Vs a single endedpreamp ,or Direct Heated Triode which has only one stage ,
    And on top models No capacitors in the output signal path ,just the output transformers.
    You just need to choose a tube that is very linear and a true DHT tube ,the big300b tube is a DHT used mainly for a amplifier output tube for example ,the 45 tube is a great low power tube to use. I myself use what was a German tube ,that the Russians improved upon the 4P1L Vacuum tube , considered by many possibly the most Linear tube and very exceptional sounding and accurate .microphonics are the only down side regarding sensitivities to cabinet isolation . Which can be down with proper care . One thing very over looked is the tube sockets Gold over High purity Copper, or Phosphur Bronze are the only ones I use brass is vastly inferior and you can without question hear the resolution differences.most others are all Vacuum tube preamps Indirect heated triode such as 6sn7,6922,12ax7, 12au7. Direct Heated Triode, as in amplifiers are by far the most accurate for pulling information from the record, or disc.
    I am speaking of only from my experiences with preamplifier up to $15k
    I am fortunate to have a friend that just builds single ended Vacuum tube amplifiers , most people don’t want to go through all the decisions .this PS audio BK design is a very good one though .
    And preamplifier .

  3. We had this discussion in an earlier thread. I disagree. I owned a Placette Remote Volume Control that was literally nothing. I’m convinced no one will ever make anything more “nothing” than that. The lack of distortion at first was seductive, but it ultimately lacked drive, musicality, etc. The result was purely uninteresting. It’s counter intuitive, but there is something to an active preamp that is additive to the music reproduction process, distortion and all. What I learned from that exercise is that distortion is not always a bad thing, and total removal comes at a cost. The analog volume control in my preamp may add some distortion, but I will no longer discount that the distortion it creates adds to the overall sonic presentation.

    1. I never found my Placette to lack musicality, only drive. It always transmitted whatever musical properties were produced by the source component. But I do agree that a good active preamp adds something to the process, more like body, but not distortion to my ears.

  4. In my Msb dac there is two ways they claim in improving the output
    One is on my model a single gain stage is used on the new select 2 there is no gain stage. It’s inside and done on the da converter chips.
    I think as audio evolves each maker must show a path to how there product is improved over the past model. And ps audio is no different

    It’s a thin line to walk to claim improvment but not trash the past.
    Paul being more honest than most in this.
    On my Cust gg head dac by lampi I can roll
    Many tubes and add or bypass the driver as it does lower the gain and difrent tubes do have varying gains
    It’s not a vol control. What lampi does I have no idea but it does not seem to effect the sound at lower levels and nor does my Msb as it goes from passive to active passing 0 DB. I think anyone making a device at this point should have a minimal effect on sound. As for stages and purity I think the end result is what we hear and while measurements are important it’s always what we hear. If I measured my lampi and compared it to my Msb or even the ds dac I’ll bet being tubes it would measure worse but it’s sound is better in my system.
    For discussion it’s fair to post but maybe there should be some reality added to this post something that less than Suoer human ears can hear as well.
    Happy Father’s Day to parents and grandparents

    1. “Happy Father’s Day to parents and grandparents”
      Absolutely. Big barbie and Champions Trophy final on the TV. (To Americans, that’s cricket. India v Pakistan, global audience around 1 billion, excluding my wife who’s a non-believer.) Then out for a curry. Went to see the Queen yesterday, wished her happy birthday, trooping the colour, fly-past with Spitfires and the Red Arrows. Not a weekend for audio or pre-amps.
      http://www.mirror.co.uk/news/uk-news/gallery/kate-george-charlotte-steal-show-10638638

  5. Paul, I may continue to buck the current trend but I don’t consider you are talking about preamplifiers. Instead they are line stages.

    Prior to the mid-80s with the advent of digital players, almost every control device (preamplifier) included a phono stage. They also contained input switching, output controls (balance, bass and treble, filters, tape selector, etc.), and gain as you suggested. But with the growth in popularity of digital players (CDs) and the abandonment of phono systems by a growing number of hobbyists, many of those features were eliminated and the replacement components were commonly called line stages.

    This still creates some level of confusion but for us “old timers” the term preamplifier suggests a component with far more functions than is commonly available today.

  6. Please make a small compact Gain Cell preamp for desktop use? The Gain Cell preamp now being offered is way too big for my desktop use. Desktop use does not usually require lots of inputs. Small… (external power supply to keep it small?)

  7. Variable gain by nature requires something being introduced or removed from the amplifying chain to attenuate the signal or increase it and this would certainly introduce a change in sound. So the point is whether it is better than a volume control. Regards.

    1. When done properly, a variable gain solution does a lot more than just eliminate the intrinsic sound of a given analog attenuator.

      For one, the source now sees the same impedance regardless of the volume setting, and perhaps more importantly, the signal to noise ratio remains constant. With a fixed gain product the noise level is constant, but as the input is attenuated the ratio decreases. With variable gain the noise level decreases at the same rate as the signal keeping the S/N ratio intact.

  8. Well I hate to be the one to break it to you but every gain stage in the entire chain has the signal go through a resistor, that is unless you have learned how to bias transistors and vacuum tubes without them. The path the signal appears to travel from the output of one stage to another is not the actual signal path. The real path travels from the power supply through a resistor through the transistor or tube and into the load which is the input of the next stage or speaker. The volume control on most circuits only adjusts the gain between stages at one point.

    Another problem is that in the recording process, there are a lot of volume controls. the signal passes through. You can’t eliminate their effects either.

    1. Great read and I had the same thought. Paul could you educate us on the difference in volume control between the Gain Cell and what implemented in DirectStream and DirectStream Junior.

      1. The Gain Cell is a variable gain analog amplifier while the DS and Jr. are digital volume controls. Very different. A digital volume control actually changes the bits to reduce volume. The way Ted does this is very clever in that it does not change sound characteristics. I wish I understood that process better.

        The Gain Cell obviates the need for a volume pot because instead of a variable resistor shunting music to ground into a fixed amplifier, the amplifier itself changes its gain.

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