Complementary Zen- class A or AB?
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 21st April 2004, 10:30 PM #1 needtubes   diyAudio Member   Join Date: May 2003 Complementary Zen- class A or AB? HI- I have seen designs such as this that are labled Class AB (example, the SDS headphone amp) and then the Zen that is labled class A. Which class is this amp? Is it just a matter of bias current? What I mean is if you bias the amp at 2.2A per channel, it will run class A up to 2.2A out, then become AB for everything above. Is this remotely correct? Could this circuit be adapted for lower power (around 1W instead of 20 or so)? Thanks
 22nd April 2004, 12:04 AM #2 Nelson Pass   The one and only     Join Date: Mar 2001 It's just the bias current. If the amp is a push-pull type, the output current peak will be twice the bias current, so if you bias a 1 amp, it will leave Class A at 2 amps. Into 8 ohms, this would be I^2 * R which is 4 * 8 = 32 watts peak, which for a sine wave is 16 watts continuous. It will usually operate AB above these levels. If the amp is a single-ended Class A biased by a constant current source or an inductor, then the peak output current is equal to the bias current, and will not deliver more. If a push-pull Class A amp has a varying bias circuit, and there seem to be plenty of them around, then you can set the ratios anywhere you like, but the performance tends to suffer at lower bias figures. If a single-ended Class A amp has a varying current source like an Aleph, then you can set the figures where you like, but they are only pretty within a limited range, usually not higher than peaks of twice the bias.
 22nd April 2004, 12:43 AM #3 needtubes   diyAudio Member   Join Date: May 2003 Thanks! That pretty much cleared everything up for me.

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