Henry Azima: A Mission to Succeed Page 2
John Atkinson: You say that choice of components is important in amplifier design. As an ex-military engineer, did it come as a shock to find that the choice of coupling capacitors, for example, was important when it came to sound quality?
Henry Azima: Absolutely. And we learned through a lot of heartache that to source good components was very difficult. We have now established a relationship with many good suppliers in the UK, who can supply components according to our specifications. Fortunately, our volumes with Cyrus are fairly good, meaning that we can get things at reasonable prices. So I think we are now using the sort of components we have always wanted to use. In the Cyrus 2, for example, all the capacitors below 10nF are polypropylene, which we believe is one of the best types. And although we use electrolytic coupling capacitors, these are the best we know of.
John Atkinson: You haven't thought about using DC servo-circuits so that you can get rid of even those coupling capacitors.
Henry Azima: Maybe in the next generation, but to do it that way, especially in the preamplifier, makes the circuitry more complicated. Albeit we haven't tried it as such, but it may not prove actually as good sonically. In theory, I could probably make the Cyrus amplifier better, but there are production and engineering problems with a such a physically small amplifier. You see, all the circuitry is on one board. The price I would have to pay would be to compromise the optimization of the layout.
John Atkinson: And if you did it on more than one board, the price would go up commensurately and the amplifier would be less competitive.
Henry Azima: And, of course, the maintenance and the service cost would go up as well. I think that, as well as the fact that it's a good-sounding amplifier, one of the beauties of Cyrus's design is that it's a joy to work with, to repair or to change anything, because it's very simple.
John Atkinson: There does seem to be a correlation between good-sounding amplifiers and simple, direct circuitry. It's been suggested that one reason why tube amplifiers sound good is not due to the use of tubes but because they tend to have very simple circuits, with very short signal paths. That would also explain why a typical Japanese amplifier doesn't sound as good as it should because it has a very complicated printed-circuit-board layout, and the signal is actually taken in a very complicated manner from input to output. The Cyrus design, with its very compact power-amplifier layout and line-level inputs taken straight to the selector switching and volume control, appears to have as direct a signal path as you can get, given the compromises inherent in an affordable one-board design.
Henry Azima: Absolutely. In fact, I would like to take a sidestep and compare this with the business of single-strand cables, which are now coming into fashion. This primarily started in the UK, with people like Denis Morecroft working on it, and Mission also intends to produce speaker cables and interconnects in single-strand form. I think that the comparison here is that single-strand has got one simple path, whereas with multistrand, however good the quality of the single strands which constitute the cable, you've got a multipath problem. You have the effects of corrosion between the strands, you have got all sorts of diode effects.
John Atkinson: But two things worry me with single-strand, solid-core speaker cable. One is that conventional single-strand house-wiring cable, as sometimes recommended in Hi-Fi Answers, is not very pure copper. It's very brittle; if you bend it too many times, it snaps. The second is, how do you get the resistivity low enough?
Henry Azima: What we are trying to do is to shoot for a 1.5mm-diameter, pure copper wire. Once you lay a cable around the house, you won't really move it again, so provided that you can actually dress it around the carpet, etc., that's it. It should be fine. One problem, I think, with the thickness that Morecroft is going forhe's apparently trying to do it with 0.67mmis that the series resistance will alter the Q of the loudspeaker. It will also change the frequency response with anything but a purely resistive loudspeaker. But 1.5mm cable would have, I think, sufficiently low resistivity that you could forget such problems, especially in a normal listening environment where you won't use more than 3 to 4 meters.
John Atkinson: To return to amplification, I noted with interest that although the Cyrus power-amplifier section is based on discrete transistors, you use op-amps to implement the Cyrus's disc circuitry. There seems to be a strong feeling among American audiophiles that op-amps are a no-no for high-end design, there being so many bad-sounding products using them.
Henry Azima: Well, obviously the choice of the op-amp is extremely important. We use the best type available for audio applications: the NE5534. The ones we specify for Cyrus are the AN type, which are preselected, with guaranteed low noise. These are made by Signetics, the designers of the 5534, and they're reliable and always within specification. They are absolutely fantastic. We have never had one go out of spec.
John Atkinson: That's all right, of course, as long as you can guarantee your supplies! My own experience has been that, if you choose to use op-amps, you must design with as much care as you do using discrete transistors. I get the impression, from looking at some CD-player output stages for example, that many designers regard op-amps as magic bricks with programmable gain. They just drop them into the circuit without a thought as to the specific requirements of the IC.