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RE: Ping Charles Hansen - Integrated amp question

Posted by Charles Hansen (M) on July 6, 2012 at 07:59:35

In Reply to: RE: Ping Charles Hansen - Integrated amp question posted by Belgarchi on July 5, 2012 at 18:26:28:

I don't disagree with you. As I wrote my post I really had solid-state in mind. Just about any pure tubed circuit (including the power supply) will sound musical and enjoyable. However the sound of a single-ended tube circuit is extremely sensitive the the power supply used.

Let's focus on preamps for now, because 99% of all tubed power amps have a balanced output stage (and virtually all current Audio Research power amps are fully balanced from input to output).

Listen to a classic "old" product like a Dyna PAS-3x. The sound will be warm and musical, but also lacking in resolution with mushy bass. This is because the power supplies in those days almost universally consisted of a string of electrolytic capacitors with isolation resistors between the stages. The inside of an electrolytic capacitor is full of a gooey gel (the electrolyte) and it is no coincidence that the sound of this type of product can be fairly accurately described as sounding like a "gooey gel".

For the last decade or so, C-J has gotten rid of the electrolytic capacitors in their preamps, replacing them with either polystyrene or Teflon film capacitors. These sound much better than traditional electrolytic-based power supplies. There is much higher resolution and the bass is not "gooey" sounding.

Another approach to power supplies is to use regulators. The first tube preamp to use a regulated power supply (to the best of my knowledge) was the ARC SP-3a. This had a zero-feedback emitter follower regulator and sound *much* better than the competing products of the day. (In fact I think I could still be happy owning one of these.)

Then the modifiers came along. In the late '70s there was a famous (at the time) mod called the "Paoli power supply", I believe because the company (probably a one-man garage-based operation) was located in Paoli, Penn. It had a new regulator PCB that replaced the zero feedback emitter follower with a high-feedback op-amp based regulator. At first everybody raved about it because it increased the detail and resolution dramatically. Over time everyone became disenchanted with the sound because it made the SP-3a sound a lot like an solid-state op-amp based preamp -- kind of hard, edgy, and grainy.

I think probably the best sounding single-ended tube preamp made is the CAT SL-1. Ken Stevens also uses zero-feedback discrete solid-state regulators, similar to the SP-3a, but much more sophisticated and highly evolved. Of course the typical low-resolution volume potentiometer is replaced with a high-quality stepped attenuator using silver-contact switches, and there are many other improvements that increase the performance of that unit.

But the bottom line is that a single-ended circuit is supremely sensitive to the quality of the power supply. On the other hand a true balanced circuit will reject imperfections in the power supply in the same way that balanced inputs will reject hum pickup in long cables (which is why recording studios use balanced circuits almost exclusively).

In my experience one can make a great sounding single-ended tube product. The main thing is to keep everything in the "tube domain" as much as possible. For example one of the recent upgrades to the ARC Ref XX preamp largely consisted of replacing the solid-state rectifiers in the high-voltage supply with tube-type rectifiers. However I am also firmly convinced that no matter how good a single-ended product sounds (tubed or solid-state) that an equivalent fully balanced product will sound even better. The penalty is that the cost of the circuitry will pretty much double. On the other hand the actual circuitry is often a relatively part of the total cost, as things such power supplies, connectors, chassis, and so on really add up.

While I enjoy the sound of a good tube-type product, I am too old and busy to mess around with them any more. When I was in my twenties, it was fun to do "tube rolling" or look for vintage NOS tubes and so forth. But now I have a family and a business to look after. I don't have time for tubes any more. So I design and build equipment that I would like to own. For me this means solid-state and a freedom from having to schedule maintenance.

With solid-state I think that it is even more important to use discrete, balanced circuitry to achieve the desired performance level. For one thing even most the "balanced input-balanced output" IC's convert to single ended at some point internally. My goal is to make solid-state products that provide the same listening pleasure as a good tubed product while retaining the low "fuss factor" of solid state. I feel that using fully-balanced discrete designs has allowed me to reach this goal.

Hope this helps,
Charles Hansen

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