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|1st June 2003, 11:24 PM||#1|
Join Date: Feb 2001
'Evil Twin' of Zen V4
I think the 'Evil Twin' of Zen V4 is appropriate for this.
I don't have the capacity to post a schematic so I ask you to refer to the one at Pass Labs for the Zen V4.
Imagine building a mirror image of the Zen V4, reversing all the transistor and power supply polarities. Parallel the inputs. Now delete the current sources for the outputs. See how the feedback resistors and the speakers are hooked to B+ and B- respectively?
Hook it up like this, delete Ra, Rc:
The bias trim pot for the N side sets the overall bias, the bias trim pot of the P side then becomes a DC null when the bias currents match.
Another visual aid, this one with BJTs:
This is of course a standard power follower design, National Semiconductor sells a couple like this. The capacitor allows for class AB output after it runs out of bias. This would make a fine amplifier as is except for the high drive current required. A FET design would take care of that.
Because the main ± for the outputs goes away as the voltage swing increases, we need a ±15V or so for the bias voltages for the FETs. Since the speaker and feedback will connect to the transformer center tap, one transformer winding will be needed for each channel(mono-bloc construction). The bias supply may be common to many channels, the preamp, a crossover, etc.
Because the sources of the FETs are grounded, an active bias with a load current sense could be added (think Aleph).
The 'Evil Twin' would be essentially a push-pull varient of the Zen V4.
I have this drawn out on paper and can snail mail it to anyone able to post it as a GIF, JPG, etc.
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