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Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
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Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
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In Reply to: Re: P.S. posted by Dan Banquer on March 12, 2007 at 09:25:14:
"Duh"No Duh there Dano. I have seen PLENTY of SS amps with high order harmonics much higher in level and also extending well beyond 20kz for a 1Khz signal (so even over 20th harmonic). In addition, they are mostly odd harmonics...the most offensive.
The third, 4th, and 5th are audible but at what levels? Do you know? 2nd is of course inaudible up to quite high levels but we are talking about -75 db, -95 db, and -100 db at 1 watt. Probably not so audible because masking can still occur for these harmonics (ie. the ear still makes distortion at these harmonics). The complete absence of anything 6th or higher (at least they are below -125 db, which is the measured noise floor above 1khz)is the really interesting story.
At 10 watts those were -55db, -70db and -85 db. HOwever, this will likely be less audible because it will be much louder (with a 95db speaker likely too loud) and your ears own distortion may still mask the distortion (see cheever).
The real problem, Dano, is the higher order harmonics present in a complementary, Class AB amp with high feedback at LOW power, where most listening is really done. Found a cure for that crossover distortion and high order harmonics? Didn't think so. Feedback doesn't fix it, Dano. Feedback MAKES high order distortion, while reducing low order distortion. Read Crowhurst or Boyk and Sussmann.
It is also clear from Boyk and Sussmann's triode tube model why my amp has some low level high order harmonics when the power increases. However; it is clear from their work also that for the same input level the tube produces far lower levels of higher order distortion, which is why at 1 watt they are well below the -125 db noise floor. I think we can both agree that below -125 db it is likely to be inaudible, no?
Crowhurst talks about signal correlated noise floor, something that is really only possible with negative feedback. As the so called "noise floor" is really made of multitudes of harmonic components it will increase and decrease and modulate with the input signal. This can't happen with a no feedback design. What about back EMF distortion from highly reactive speakers? He says that although the level is quite low the high order nature of the distortion could possibly be audible and could be why amps can sound so different from speaker to speaker. Care to comment on that or was Otala a quack too?
Cheever found a way to measure a Hafler DH500 without the feedback interferring and found the THD to be 24%!!! Of course with feedback this amp wipes the floor with yours in terms of THD. I doubt either of us would find it particularly good sounding.
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Follow Ups
- Re: P.S. - morricab 11:00:47 03/12/07 (2)
- Bwahhhhhhhhhhhhhhhhhh! - Dan Banquer 12:55:39 03/12/07 (1)
- Re: Bwahhhhhhhhhhhhhhhhhh! - morricab 14:05:36 03/12/07 (0)
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