a_recording
Member of the Trade: Lachlanlikesathing
- Joined
- Mar 20, 2009
- Posts
- 4,705
- Likes
- 793
Just found this thread. Have to say, props to the OP for collating such a broad set of results!
So you're telling me a modern, cheap solid state amp will perform just as well as my Quad monoblocks?
Originally Posted by gedlee You can believe it or not, but its true. I tested about five amps that I had and the Pioneer was the best. People always take my statements out of context. Once one has good electronics - and clearly price and "personal perception" don't correlate with good - then the only thing that matters is the speaker and the room (source material being a given). I have never said that any piece of junk electronics is fine. Only that very inexpensive and readily available electronics place the electronics into the "insignificant errors" category. I know that this is not a popular position and it's not one that I have always held, but I have studied this problem intensely and this is my conclusion. It is, by the way, the same one as held by Flyod Toole and Lauri Fincham and a whole host of other well know audio researchers. It's amp designers and marketers who seem to hold contrary beliefs |
Originally Posted by gedlee No hardly - I don't "favor it", but I was severely chastised for using it at RMAF when, in fact, no one really knew if it was any good or not. It works just fine as my measurements show. I would not use this amp for many applications, but it suited my point at the time, which was that loudspeakers account for 99% (well you could argue 98%, but you get my point) of the audio systems sound quality. The amp is a Pioneer DSX-V912 - a receiver. The point is that it was on sale at Costco for $150.00. I bought several of them for home theater use. I used my test to measure the amps and they were quite good actually. Especially for chip amps. I was measuring a lot of chip amps (a survey of capability) and most were pretty bad. As a chip amp this unit definitely stands out. It compared quite favorably to a very well engineered discrete amp that I also use. I also tested several other receivers and they were almost universally bad. |
Originally Posted by gedlee Crossover distortion is a particularly insidious form of nonlinearity because it happens at all signal levels and there is no comparable mechanism in a loudspeaker to mask it. The question was asked if I have a way of identifying crossover distortion in an amplifier. Yes, I do. You see the situation with crossover distortion is that the % distortion increases with falling signal level. This is exactly why it is so audible since this is directly opposite to our hearing. One could therefor ***** crossover distortion by looking at THD as the signal level goes lower, which is a typical measurement. The problem is that virtually all of these THD versus level measurements are THD + noise. When this is the case, the rise in THD at lower signal levels is actually the noise and NOT the distortion, but it is impossible to tell which is which. SO this test actually masks the real problem. One would have to track the individual harmonics of the waveform, but then the noise floor is still an issue. Hence the measurement problem is one of noise floor and how to measure distortion products down below this floor. This is done by averaging. But normal averaging can only lower the noise floor so much - down to the noise power. But if I have a signal and I average this signal synchronously then I can raise the net signal to noise level. This too is common. But if the signal does not exactly fit the time base then I need to window it and the resultant spectral leakage makes this synchronous averaging less effective. I use a signal that exactly fits into the time base of the A/D taking the data. This means that I don't have to use a window and I can synchronously average a signal to noise ratio that is about 20 dB better than a simpler test could achieve. This means for example that the input signal needs to be something like 976 Hz, not 1000 Hz, which doesn't exactly fit the window. I actually had to generate the input wav file in FORTRAN using quad precision, special random number generators and rounding techniques, because the test signals needed to have a 120 dB dynamic range - very difficult with 16 bits. I use a signal that starts out low and goes up in level. I plot out the results as the signal drops into the noise floor. This test shows vast differences in amps that measure identical with standard tests. It also shows that my Pioneer amp - you know the "really crappy" one that I get criticized for using at RMAF - is an extremely good amplifier. As good as the best that I have tested with this technique. |
some AB amps, audio chip amps do show rising distortion as output level goes down - well above the noise floor
I don't know that Geddes pursuit of low level/crossover distortion deep into the noise floor is warranted - but some AB amps, audio chip amps do show rising distortion as output level goes down - well above the noise floor
and this really isn't captured in the side of the box specs - although easily seen with THD vs Power sweeps - preferably at a number of frequencies
Geddes has the listening test results for our greater sensitivity to these distortions
many consumer mass market amps still game the power specs - although you can now find the weasel words if you look closely since the FTC set some standards