In Reply to: RE: Yeah, I get that- seen it in spades. posted by morricab on October 18, 2021 at 05:17:04:
One of the most disturbing effects of negative feedback that I have heard is this loss of natural dyanmics. The sound is so tied down that it no longer breathes like it should. I think that when you are feeding back the output to the input you are also somehow blunting these dynamic cues from the music...you are not only removing distortion (or creating new harmonics).
Yes- I've heard that too. That is why the feedback in our smaller amps (S-30 and M-60) is really minimal (2dB) and zero in our larger amps.
But that isn't a function of feedback as it turns out. Its a function of not enough feedback. And its not enough to say its not enough, because you can point to a Futterman OTL which claims to have 60dB (which it does at bass frequencies). At higher frequencies (like so many other amps out there) it has considerably less, owing to a lack of enough Gain Bandwidth Product.
Dynamics should come from the recording. The amp should not mess with that in any way. And they don't; the problem is distortion affects how we perceive the dynamic contrasts. If you don't have enough feedback you can have proper presentation in the bass, but as frequency goes up, things get messed up. There's more higher orders so while the bass might right, the highs are not.
If you have enough gain bandwidth product you can get around this problem. What you're looking for at any rate is a distortion figure that is the same at all frequencies. You can do that with zero feedback if you have enough bandwidth. Or, if you can get enough GBP you can do it that way, but you have to have enough GBP to support 35dB or more at 20KHz.
At that point the 'dynamic compression' you seem to hear with lessor amounts of feedback goes away. The sonic signature of the amp is another matter; it still needs to have the proper distortion signature (lower ordered harmonics as the dominant distortion product) even though that distortion might be quite low.
I've seen many 'objectivists'(?) (people who simply look at the specs) denigrate high end audio amps as 'tone controls'. In a way they are right, the problem they are having is they are not being pragmatic to understand that distortion is never going away. So if its not going away, you have to make sure that its as innocuous as possible. That will allow the amp to sound like music.
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Follow Ups
- RE: Yeah, I get that- seen it in spades. - Ralph 09:54:58 10/18/21 (12)
- RE: Yeah, I get that- seen it in spades. - morricab 05:43:08 10/20/21 (10)
- RE: Yeah, I get that- seen it in spades. - tube wrangler 18:17:44 10/20/21 (5)
- Class D gain - Ralph 11:06:50 10/22/21 (4)
- RE: Class D gain - tube wrangler 12:49:39 10/23/21 (3)
- There are zero feedback class D amps- some are getting very good comments too. nt - Ralph 09:36:31 10/25/21 (0)
- RE: Class D gain - morricab 02:59:11 10/25/21 (1)
- RE: Class D gain - tube wrangler 12:57:48 10/25/21 (0)
- RE: Yeah, I get that- seen it in spades. - rivervalley817 14:22:27 10/20/21 (0)
- BTW, thanks for your posts! nt - Ralph 09:07:37 10/20/21 (1)
- Same to you...good discussion! nt - morricab 14:03:43 10/20/21 (0)
- Yes!! - Ralph 09:05:40 10/20/21 (0)
- RE: Yeah, I get that- seen it in spades. - tube wrangler 11:27:06 10/18/21 (0)