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Old 11th March 2013, 07:44 PM   #8591
dvv is online now dvv  Serbia
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"... higly specified ..." - now, THERE'S a can of worms.

I can't even remember all the times I was let down by higly to extremely well specified products. I realized in the late 70ies that specification have, practically speaking, nothing to do with sound quality.

An ultra low THD and IM spec would suggest that the amp sounds good, yet far too many such highly specified amps don't sound good and involving at all. It's not just getting the specs, it's much more HOW you get them.

Experience has taught me that if a device uses wild amplification factors and lots of global NFB, chances are it'll sound shut down, dark and/or bland.

The other extreme, no global NFB, sounds much better, but also not right - I have yet to hear any such product which does not sound sort of unfinished, short of the mark, a little loose.

It seems that in audio, as in life, it's the golden middle that gets the prize.
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Old 11th March 2013, 07:50 PM   #8592
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Quote:
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It seems that in audio, as in life, it's the golden middle that gets the prize.
interesting.
for instance, middle women leave me cold it's the crazy, reckless type that gets me going. to each his own
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Old 11th March 2013, 08:46 PM   #8593
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I don't know what a "middle woman" looks like.
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Old 11th March 2013, 10:39 PM   #8594
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As I sometimes say, the right amount of feedback is the right amount of feedback. People who believe that 'none' must be best (however poor the amp), or that 'lots' must be best (to hide a poor amp), are both missing the plot. Sometimes 'none' is the right answer. Sometimes 'lots' is the right answer.

However, I am sometimes suspicious of claims that high feedback amps are bland or clinical. I wonder whether such folk are merely expressing a preference for a little distortion with their music. Too much feedback would actually lead to either instability (or at least ringing) or sharp clipping; neither of these would sound bland.
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Old 12th March 2013, 07:51 AM   #8595
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Quote:
Originally Posted by DF96 View Post
As I sometimes say, the right amount of feedback is the right amount of feedback. People who believe that 'none' must be best (however poor the amp), or that 'lots' must be best (to hide a poor amp), are both missing the plot. Sometimes 'none' is the right answer. Sometimes 'lots' is the right answer.

However, I am sometimes suspicious of claims that high feedback amps are bland or clinical. I wonder whether such folk are merely expressing a preference for a little distortion with their music. Too much feedback would actually lead to either instability (or at least ringing) or sharp clipping; neither of these would sound bland.
Dave, there are always exceptions to just about any rule I can think of.

Think back a few months to the example I named, and supplied its schematic diagram, the German made LAS power amp. It is truly an outstandinding example of a strangely designed amp, which had no right to sound as good as it did, but it stuck its finger in my eye and managed to sound really good. Seriously good, even if I have heard better even then.

1.5 Ohm/17W emitter resistors? Using power devices rated at 100V with +/-50V rails? Isn't that shaving it too close? Using a wildcard of sort, since BFT28A transistor was made by a very lonely California company only? Open loop bandwidth iof just 4 kHz? Lots of global feedback? Zero input stage degeneration? No resistors even for the current mirror?

Yet, just 5 minutes with it will convince you that those people knew EXACTLY what they were doing, and the some.

Obviously, using just that one example (and there are more), it's perfectly clear that it's quite possible to use a lot of global NFB and still end up with an excellent product. Even, in some cases, a very advanced product most manufacturers have not made to this day, and that one was from 1978 or so.

I agree with you that it's not just the feedback scheme. If you design from the start for high global NFB, you'll very likely go about it differently than otherwise, and may well end up with a good sounding amp. It's the undecided, the half way houses, who suffer the most, in my view.
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Old 12th March 2013, 07:59 AM   #8596
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However, I am sometimes suspicious of claims that high feedback amps are bland or clinical.
I'd say most good measuring amps are reported by the press to sound that way.
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Old 12th March 2013, 08:50 AM   #8597
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Dave, here's a cute test you will end up loving (I think).

Step 1. Go to any e-bay (German, British, etc) and find a Harman/Kardon integrated amp model 6550. It's rated at 50/70W into 8/4 Ohms. It uses just 17 dB of global feedback.

Step 2. Refresh it, meaning exchange each and every capacitor inside, starting from the two main electrolytics. Do not install parts obviously way above what was originally used, although I would suggest you use silver mica for small value caps.

Pause after Step 2. Listen to it, learn how it sounds. Then go to Step 3.

Step 3. Exhange the shitto volume pot for an ALPS Blue.

Step 4. Meditate and prepare yourself for the surprise of your lifetime once you hear it. Space, air, stage width, depth and heigth like you would never expect from a commercial product, and rarely hear even with High End devices. Yet, sound full of energy and impetus.

It could be your prized component for a long, long time. Frankly, I have never heard such high quality sound from a mass produced component in my life, and believe me, I've heard a lot of them.
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Old 12th March 2013, 09:01 AM   #8598
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Hello !
I have a curiosity.
Let's take, as an extreme, a single ended zero feedback tube amp
then select a speaker that sounds very good with the SET above mentioned.
Then take a solid state high feedback amp and use it with this speaker
What would it be the sound ? bland and clinical ?
I do not know really, but maybe it could be a worthwhile test
The comparison must be made with same speakers.
I think it is almost never the case
Kind regards,
gino

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Old 12th March 2013, 09:42 AM   #8599
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The frequency response will be quite different. If you want an equalizer, there are easier ways to make one.
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Old 12th March 2013, 09:43 AM   #8600
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Originally Posted by DF96 View Post
As I sometimes say, the right amount of feedback is the right amount of feedback. People who believe that 'none' must be best (however poor the amp), or that 'lots' must be best (to hide a poor amp), are both missing the plot. Sometimes 'none' is the right answer. Sometimes 'lots' is the right answer.

However, I am sometimes suspicious of claims that high feedback amps are bland or clinical. I wonder whether such folk are merely expressing a preference for a little distortion with their music. Too much feedback would actually lead to either instability (or at least ringing) or sharp clipping; neither of these would sound bland.

I once asked Michael Gerzon about this , his answer was much the same . I started by saying what were his thoughts about negative feedback . His answer " well , I never have , had I I might have said this . Some amplifiers need a lot and some virtually none , after a pause with a giggle " you can be sure of one thing , nearly all will have the wrong amount " I didn't need him to say more , however he said this . Suppose you have an amplifier with either 3 or 4 stages , both cause problems . What you need is 3.7 stages . Obviously Michael although very good at maths and the most difficult problems obviously knew less about amplifiers . For once in my life I kept my mouth shut . I was tempted to say degenerate the VAS a little . Arguments rage about that and as Douglas Self wrote to me it is the worst idea of all as it doesn't bring the expected benefits . I do it because it helps match stages better ( lifts the base voltage for one ) . Sound wise 0R = punch 47R = soft and spacious 16 R = just right . This was 8 mA VAS and 2 mA LTP . Measurements were mostly identical either way . I never tested IMD for this , my hunch is it has an effect . This seems even more effective with 1970's amps . Raise input current , add a VAS emitter resistor . The Goodman's 80 has a diode in the emitter . Replacing that with a 56R resistor seems to do a lot of good . DC conditions are unchanged . When I see valves with LED's in the cathode I often wonder if it is a good idea due to the Goodman's . The Goodman's was terribly harsh before the mod . Transistor sound or IMD . The guy my brother did this for paid 100 for the work . His joy was taking it to hi fi shops to defeat all-comers . The other mods were polystyrene , polyester , high grade electrolytic caps . Also DC levels checked and set . We often worked together . Me with the ideas , him at the test station . 100 would be 300 now .

I have told these stories before so please forgive .

I don't think people who prefer low feedback amps are wrong . Equally I have heard plenty of high feedback amps that sound great . Take my favourite cheap op amp MC33079 ( 78 ) . I much prefer it with gain 1 over gain 2 . 2 sounds less focused . Up at gain 62 it also sounds fantastic ( MC stage ) . Between 2 and 62 I am not so sure . A friend I built a preamp for is both musician and PHD in electrical engineering . We worked through this for fun and did find that truly there was evidence to support this . Our conjecture is that unity gain was so much a priority that it fashions the performance . I prefer 33078 over NE5532 . The one thing I would like is a MC33077 single version with all the 5534 tweaks ( comp , offset ) .
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