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Old 24th August 2007, 11:29 PM   #1
jaycee is offline jaycee  United Kingdom
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Default The "Classical Class A" amp ? Comments?

I came across this a while ago:

http://home.no.net/andiha/articles/audio/claclassa.htm

I've not seen the use of that buffering arrangement on a power amplifier output stage before.

Also, to me, the amp doesn't really seem to be Class A, rather just high biased Class AB.

Anyone else got any comments, maybe someones tried it ?
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Old 25th August 2007, 12:19 AM   #2
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a quote from the link:

Class A operation means that all transistors in the amplifier draw current all the time, until the amplifier start to clip, caused by a too large input signal. When such an amplifier shall drive low impedances, e.g. 4 or 8 ohms, it is necessary with a considerable current consumption. This causes heat that has to be removed.

The large current consumption gives us, however, one of the benefits of class A operation, namely a distortion that is low and kind to our hearing. A transistor initially is a very nonlinear component, and one way to reduce the influence of these non-linearities, is to limit the drive of the transistor.
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Old 25th August 2007, 12:53 AM   #3
fab is offline fab  Canada
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Default Re: The "Classical Class A" amp ? Comments?

Quote:
Originally posted by jaycee
I came across this a while ago:

http://home.no.net/andiha/articles/audio/claclassa.htm

I've not seen the use of that buffering arrangement on a power amplifier output stage before.

Also, to me, the amp doesn't really seem to be Class A, rather just high biased Class AB.

Anyone else got any comments, maybe someones tried it ?
The buffering is a "diamond buffer" stage. See my post at http://www.diyaudio.com/forums/showt...59#post1120959
Unfortunately, I have not completed this project but switched to other ones...

The site you mention indicates 1.8A bias so it can certainly do class A to a respectible power level.
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Old 25th August 2007, 01:58 AM   #4
jaycee is offline jaycee  United Kingdom
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I've been trying the diamond buffer out on a topology similar to the SymAsym amplifier shown here (but with higher power, using KSA1381/KSC3503 in the 2nd stage) as an alternative to my usual "triple darlington" (a la Leach).

So far, I'm not convinced the complexity is worth it, it also seems to make bias harder to regulate.
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Old 26th August 2007, 03:45 AM   #5
fab is offline fab  Canada
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Quote:
Originally posted by jaycee
I've been trying the diamond buffer ...
So far, I'm not convinced the complexity is worth it, it also seems to make bias harder to regulate.
Harder to regulate is one reason why I quit (at least for now) working on this topology. Also, I am not aware of great positive comments of the diamond buffer topology for audio amp...
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Old 25th June 2013, 08:59 PM   #6
Bensen is offline Bensen  Belgium
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As I'm starting to get interested in comparing CFB and VFB amps, I came across this circuit (see URL first post or on bottom of this). Sofar I only did build VFB amps.

My current work in progress VFB amp has an openloop bandwidth of +-4khz with an open loop gain of +-50dB. After my first simulations with CFB topology, I did not manage to get better results than the VFB amp.

In this article the author is mentioning that this amp has a Open loop bandwidth of 100Khz? This value together with an open loop gain of 46dB is impossible, not?
Am I mistaking?
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