This is blog format, so apologies on editing, length and rant factor.

It seams every year I take a single stepping stone toward the great audiophile pie in the sky. This year is it power amplifiers. A good friend is an amplifier designer and brought some power measurement equipment over to play. We listened to a number of tracks and tried a couple of amplifiers. Some amps did quite well while some well rated amps did not come close to the rated power, no surprise there. What was a surprise were the actual requirements of the amp. I had always thought 60 watts of good power were plenty, that is what my professor in college used to say . . . in 1977.

What we found is that playing most anything loud runs about 3-5 watts average. But within that average are a lot of peaks up to 300 watts or more, that is as high as my amp went. For all I know, momentary peaks could cross 5000 watts. Ray Kimber's gunshots did not register at all, too short a read for a signal that is probably uses lot of momentary wattage. At first, this was fun and that was that. But this little test tipped off a lot of thinking about power and amps and tubes and the whole shebang. What this means is that most amps are clipping at normal listening levels. It is not a question of when the amp is clipping but how much at any given point. I generally don't listen very loudly, but this test showed that even at a comfortable levels, there is some clipping.

Given the harshness of an amp that is in full clip, logic would suggest a lot of the SS harshness is minor clipping. Stay with me here, so far this is elementary but I am about to go off track and into the ditch. I am suggesting that in a concert, the lack of clipping is one major ingredient of the clarity. At home, perhaps short clips are one of the major sources of harshness. So some people use tubes to cut that clipping harshness. That would explain why a 10 watt tube amp can sound good. At 10 watts, it is only clipping a small percentage of the time. So many prefer a tube amp softening the peaks than a SS amp clipping them. The sin of omission is better than the sin of distortion. I can live with that.

So if preamps, CD players, and other line level components don't clip the sound at some point, operating within design parameters, then the need for tubes does not exist. Unless the unit is artificially voiced to sound tubey. So either a line level device must also clip or we simply prefer distorted sound. Again, if both SS and tubed line level devices clip, tubed devices will sound better for the same reason as larger amps. Or more expensive SS line level devices clip less than cheap ones. I can live with that. I got some validation of this last week in an audio shop in Berkeley, one of the few shops I have been to who a) were really nice, b) had the rooms set up pretty well and c) did not run around the rooms talking and adjusting things while I listened. But in the middle of this oh so very pleasant excursion, listening to Halcro, Wilson and CJ, the sales guy made an incredibly insightful and obvious point; "at this level, you won't hear much difference between tubes and SS". Hmmm. What he probably meant was the *I* would not hear much difference at this level. I can live with that.

What I think he was really saying was that when the wattage of the SS amp is high enough to remove almost any clipping, you don't need tubes to suppress the clips and the amps will sound similar. I can live with that. While I would never claim this narrow path to cover all the issues in amp design, I think this is clipping distortion one of the key points. The next question is why SS amp designers don't (except NAD) include a soft clip circuit as part of the basic design. My amp buddy says they are not hard to do and a number of people have done them. Must be something I am missing. I can live with that. My next question is why do people think we can hear every little phase distortion in a speaker, yet in a concert hall, the instruments are spread out all over the place and there is no planned phase relationship? Did that last Stones concert sound bad because some roadie put the bass speakers two feet back from the lead guitar speakers? Is a long row of violins all in phase to every audient?

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Copyright Peter Jay Smith 2006 Return to