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I'm not a Golden Ear. I'm somewhere around brass. There are things I can hear and that matter to me, and things that don't much. One of the things that matters to me is dynamic correctness.
I wrote a sort of mini review on an old Convergent Audio Technologies (CAT) SL1 Signature preamp we repaired. It has the best dynamics of any preamp I've heard in a system that I was familiar with. It also uses separate power supplies for every amplification stage of each channel.
I think that, along with a simple, robust topology, makes for the outstanding dynamics this preamp has.
So my tentative conclusion is that the expense and time necessary to construct a power supply for each stage is worth it if you want a no compromise design--it's not just feature and expense in search of a problem.
And no, we're not a dealer for CAT.
Follow Ups:
My friend was supposedly the northeast repair tech for Ken Stevens(CAT designer and builder), at least according to what he says. He was saying that CAT was known for it's sound, especially phono but the way it was accomplished was running the tubes right to limit. Who knows? But he did say that no two ever sounded the same back in the early CAT days because Ken would build with whatever was available at the time he got an order for one. Things progressed from there I'm sure and it all became standardized.
In the case of the two stage SET amps I've built, I agree fully about separate PSUs for the two stages having significant benefits.
I'd suggest this contibutes to good leading edges, good dynamics, and a fast responsive sound (in that order).
Of course, good power supply design is essential in the first place ... a poor PSU will sound, er, poor .... two poor PSUs will sound, er, poor X 2.
I have learnt a lot by following some suggestions from Jeff (but I have not yet tried LSES etc). I use a very much over spec mains TX (for low DCR); I use 6CJ3 rectifiers for about the lowest voltage drop of any valve rectifier (so the equivalent resistance will be low); and fairly low DCR chokes.
Then I model in PSUD for a good dynamic response using a step load. The objective I was given was that, in response to a step load increase of about 10%, the voltage drop should be regular, no oscillation, a very small overshoot and then quickly settle, over about 0.06 seconds. To get this usually requires a 2 pi PSU with small caps, and a lot of playing with values in PSUD. But it's worth it!
The combination of PSUs with good step response, and a separate PSU for the driver stage, does (in my somewhat limited experience) give dynamics and excellent fast clean leading edges; I have had such comments from expert listeners. One result is that my current best amp seems far, far more powerful than its 3.5 watts per channel ...
As ever though, there's more to good sound than just one parameter!
I quit using PSUD after the last round of "here is the new way to do things."
I'll use PSUD2 to get a rough idea of the voltage and ripple. Once I have that and the real life voltage of the circuit are checked, I just make sure the supply doesn't ring and there isn't too much hum.
Jeff is absolutely the man when it comes to layout and build quality. You will not go wrong following his instructions to the letter to build a direct coupled 2a3 amp. I wouldn't cut up any nice chokes or power transformers though. :)
Hi Lee,
I think this is an overly simplified conclusion. There are so many different ways to implement power supplies and to decouple the different stages. Also different circuit topologies interact differently with the PSU.
What does separate power supply mean anyways?
I believe that many circuits with crudely implemented power supplies will improve when separating them. But I get extremely good results with common supplies but heavy decoupling between stages.
I have seen schematics of the SL1 not sure if they had been the real deal. What I saw I would not characterise as a simple topology.
I never heard one so cannot comment on it's sound
Best regards
Thomas
Totally agree Thomas and I have auditioned a CAT SL1 in my system a very long time ago among other top rated Phono stages of the time. It was good, even very good in terms of detail but not a touch on Phono stages that I've built since.
Having taken a look at your Web site I see we share many ideas and experience and I can tell you that a CAT would not be in the same league as your Phono designs either.
Naz
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