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WSR Reber: I was going to ask, how does feedback work? What is it exactly?

Sinclair: Basically you're comparing your input signal with your output signal.

WSR Reber: The idea being they should be exactly the same?

Sinclair: Yes, except for amplitude. The problem is that once you've compared them, you've lost some time and in so doing get time smear or phase shift, and you hear this. There's a sound I wish I could describe that tells you there's feedback in an amplifier. You get more of this sound the more feedback you have. It's an unpleasant sound. It manifests itself in the upper midrange for the most part and a little in the high frequencies. Would you go along with that, Mary?

Cardas: Yes. It's kind of like jitter.

Sinclair: It's aggravating stuff. You know it when you hear a system that does all the basic things right, but doesn't grab you because there's something that makes your muscles kind of twinge.

WSR Reber: But that could be in the source?

Cardas: Sure, it's all integral. That's the key. If you're amplifying a constant tone, feedback can be very useful, because what you're looking at is exactly the same at both ends of the circuit. And every time you com-pare it along the way, it can be exactly the same. Amplifiers like this are used for non-audio purposes in industry. However, no music you are going to listen to has a constant tone for any meaningful time; it's always changing. With feedback, you're taking this moving thing and comparing it to another signal some interval later-an interval that's always too long-and using this comparison to make changes to the reference signal, which has already moved along ... changing it to a reference that is no longer accurate.

Sinclair: Signals that are highly trenchant like a human voice, a plucked string, a percussion instrument--you hear the feedback because it doesn't allow for the proper trenchant response of the signal.

WSR Reber: You are saying feedback can never be really accurate because there's a time smear, and you use very minimum to non-existent feedback in your circuit?

Sinclair: Overall, non-existent.

WSR Reber: What happens after the signal goes into the amplifier?

Cardas: Let's assume we're coming in balanced, and each channel is a full differential balanced circuit, so it's coming in...

Sinclair: Excuse me a second. The incredible noise levels in here--well, I don't think you could get this with a single-ended system. I may be wrong, but there is simply no noise here, and this is possibly the most dynamic system I've ever heard. [Neil referring to the WSR Holosonic Reference Home Theatre Laboratory-Editor]

WSR Reber: No, there isn't any noise. It just blows me away. I've never had a sys-tem like this in my life that has no noise. I attribute a lot of it to the Equi=Tech Balanced Power System and the 14 Richard Gray's Power Company Models 400S and 1200S.

Sinclair: The Equi=Tech stuff uses balanced power, doesn't it?

WSR Reber: Yes, it's true balanced power.

Cardas: Balanced power is great--for the same reasons balanced signal processing is important. In a true differential balanced circuit, each channel is processed twice: positive and negative. Any time you process a signal, changes happen as you go through the circuitry. Because you've inverted half of it, when you get to the end anything the same on both sides is noise or error. You eliminate it, which gets rid of all kinds of nasty things that can happen as the signal goes through circuitry.

Sinclair: And you get rid of them as they're created. They don't get further amplified and passed through to the speakers.

WSR Reber: As it goes through the circuitry, we get into the class of amplification, like Class A vs. Class A/B. Can you explain the differences and how your amplifiers are designed in terms of Class rating?

Sinclair: Ours are partly Class A, but we describe them as A/B. You don't get a lot of pure Class A because it would run so hot. It creates a lot of wasted heat energy.

WSR Reber: But I've always been advised that Class A is desirable, that it sounds better overall.

Sinclair: If everything else is equal, yes. The problem is when there's more heat, there's less power. It's the antithesis of what's practical for home theatre, very much like tubes. If a large amplifier, like our Dreadnaught--125 to 130 pounds, five to ten channels--were Class A, we might be able to get 25 watts a channel, and it would run much hotter.

WSR Reber: I have three two-channel, 300-watt per channel, Class A Krells, and I could fry eggs on them after watching an action/adventure movie at reference level.

Cardas: Oh, they're winter amplifiers.

Sinclair: And God knows what's coming out of your wall. Are you really getting that much power in a real-world situation, where AC lines limit? Well, with all your Equi=Tech stuff...

Cardas: Theta has come into amplifiers relatively recently.

WSR Reber: Yes, but Theta amplifiers are so wonderful-sounding.

Sinclair: They are wonderful, but the reason is because we have Dave Reich's experience. He goes back in this industry as far as you and I, Gary. Do you remember Dayton Wright speakers?

WSR Reber: Yes.

Sinclair: He was one of the engineers in the early '70s designing those gas-filled electrostats. Then he started Classé and designed the really serious stuff they used to make. He joined us about three years ago, and designs all our amps.

WSR Reber: Rather than separate power supplies, your amplifiers use a common transformer?

Cardas: We have a common transformer. Each module has its own supply. The rectification is done on each module for each channel. The benefit of having a common transformer design is that each channel can pull what it needs.

Sinclair: It's like a reservoir. There's a huge supply, and each channel takes what it needs.

Cardas: One way we can take advantage of this is when we have, say our 200-watt module. We rate this based on five 200-watt channels, each running full out. In reality, each can reach higher if needed. In a usual five-channel system, often more than 90 percent of the information comes out the center channel. Almost nothing is coming out of the surrounds, and a little something is coming out the front right and left channels. You can get significantly more than 200 watts out of the center channel because you're not drawing anything for the surrounds. It's the common transformer that allows each channel to draw what it needs.

Sinclair: We designed it so that if you go to a two-channel stereo mode from our processors, you can program it to turn off three channels of the amplifier, and this huge power reservoir is running just the two channels.

Cardas: And the others are truly in standby.

Sinclair: So little usually comes out of the surrounds that many people feed them with a small amp, but there are very short periods when tremendous amounts of sound come out of the surrounds. They need to be able to seriously push when required.

WSR Reber: I believe that the quality of the amplification should also be identical in all channels. What's interesting is how one manufacturer can claim a 100-watt-per-channel amplifier, while another will claim a 50-watt-per-channel amplifier, yet the 50-watt amp will out perform the 100-watt amplifier. Why is that?

Sinclair: It's the nature of the measurements. The measurements are steady state. They don't have much to do with real performance on highly transient material.

WSR Reber: Wasn't that standardized years ago?

Sinclair: Not in a way that truly relates to real usage. It's like measuring a car's performance on a straight, smooth road and expecting it to do similarly on a canyon road with potholes. Different speakers present different kinds of difficult complex loads to amps, and real acoustic sounds are richer, more complex than test tones. There really aren't good standardized torture tests for amps, and there should be. The rule probably should be: the more dollars, the fewer watts, the better the amplifier. But then people would just raise prices.

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