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Old 30th September 2012, 11:03 PM   #131
wahab is offline wahab  Algeria
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Quote:
Originally Posted by Bigun View Post
Sometimes the compensation is intrinsic. The original JLH 10W Class A has no external compensation but relies on the parts choices - using modern high Ft devices can be a problem.
Of course , autocompensation is the trick , working even with
modern fast devices....
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Old 30th September 2012, 11:16 PM   #132
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The original three transistor circuit that the cfb configuration is based upon needed no compensation capacitor either, its just that when integration became the norm the pnp transistors in these were inferior types that needed compensation otherwise they would oscillate.

This is the point about the cfb scheme it is just a way of obtain a constant bandwidth with a fixed compensation capacitor, and it is nothing more than this, although some seem to raise it to the status of a holy grail, the last word in audio excellence, etc

You can't really hear it you know, and no you can't trust your ears, as every scientifically valid test has always shown.
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Old 30th September 2012, 11:38 PM   #133
wahab is offline wahab  Algeria
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As far as i know the usual CFB amp is a two transistors + output stage design.

Other than this , i agree on the rest , that is , that thoses amps
bring more drawbacks than advantages if ever there s any that
are relevant for audio purposes.
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Old 1st October 2012, 05:00 AM   #134
Bonsai is offline Bonsai  Taiwan
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Having now built both, I think they have their advantages.

I like the simplicity of CFA topology (see my sx-Amp, or JLH's 10 watter for example) and the fact that you can easily get decent slew rates and wide bandwidth. The open loop gain in CFA's generally tend to be lower, so you dont have as much NFB to correct for cross over distortion, so they are as a result, a natural fit with class A output stages. Some designers believe PIMD is an important issue - well the cure for this is CFA IMO.

I will still continue to build VFA amps, because I think if they are well designed they sound superb, but I would never say one topology is better than the other: its all about the execution at the end of the day.
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Old 1st October 2012, 07:11 AM   #135
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Quote:
Originally Posted by Bigun View Post
do you really mean 'sound stage' and 'mono' ? - please expand a little (I am a recent builder of a mono system)
I wasn't talking about stereo separation.
Yes, I meant soundstage, which is not impossible in monophonic.

If the equipment is good enough, one should be able to get long distance cohesion and high resolution to fill the entire house with very big, very clear audio from a (one) speaker. Lesser quality equipment will need more speakers for covering a large area.
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Old 1st October 2012, 04:57 PM   #136
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One speaker is able to expose depth in the soundstage. You'll need two to expose direction.
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Old 1st October 2012, 10:54 PM   #137
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The point I am trying to make is that with a single chanel the perceived sound stage is due to the amount of reverberation in the sound.
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Old 3rd October 2012, 03:55 PM   #138
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Quote:
Originally Posted by rcw666 View Post
The point I am trying to make is that with a single channel the perceived sound stage is due to the amount of reverberation in the sound. rcw
Assuming that reverberation and ambient sounds exist in the source recording, then are we not discussing the resolution of low amplitude signal that some amplifiers allow to pass and others do not?

Passing these signals, reasonably intact, is apparently not impossible for the VFB. But, why, with voltage feedback, is there a bigger workout with the compensations before such performance is realized?
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Old 3rd October 2012, 09:27 PM   #139
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In a word no.

If the various distortions and frequency response with a given signal are bellow the hearing threshold then the amplifier will have no audible effect upon the signal.
Those who claim a particular topology or local only rather than global feedback is superior, are never able to substantiate this in properly conducted double blind tests, and invariably go into a shoot the messenger mode and claim the test invalid.
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Old 3rd October 2012, 10:42 PM   #140
Jay is offline Jay  Indonesia
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Quote:
Originally Posted by rcw666 View Post
Those who claim a particular... rather than... is superior, are never able to substantiate this in properly conducted double blind tests
Which one is superior: Italian chardonnay or New Zealand Chenin Blanc?

The first issue there, is that the taster must be able to differentiate the taste between the two. Then he should have an idea why one is superior than the other, and that could be just about preference.

Which one is your preference: Sumatra durian or Malaysia durian?
Which one is your preference: Expresso or Luwak coffee?
Worse/best, which one is your preference: EVIAN or PERRIER?

Even IF you can taste the difference, you need (a life) time to judge why one is superior than the other. As for mineral water, it is a unique test. The different ingredient does affect the taste, but they are just mineral water without taste, aren't they?

Try this: bring 2 glasses of different mineral water. Now try and tell yourself, can you succeeded in the double blind test? Find brands such that your answer is NO (well, of course your answer would be no).

Now, change the water consumption in your house from brand A to B, and notice how much you spend/drink for each brand in each one month or two. Repeat the test to make sure that there is no coincident.

My prediction with the above is: even tho you cannot differentiate the taste in a double blind test, "your body" might be able to prefer one of them (BTW, I have succeeded in double blind test of 2 local brands)

Human body is so complex that no human can fully understand them, or how they work.

Same with audio. Even tho I found that I'm good at double blind test, I will not use it to judge if 2 things are equal or one is better than the other, because I know for sure that even if I failed in the blind test, the 2 things may have different effect against me.

So I prefer to use longer time to select my preference of an audio system. That's why I (might) have the same motto as you: "DON'T TRUST YOUR EARS" (especially if you're just a "newbie")
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