Bride of Zen output problem

Hi, I cant find solution myself, so...

Bride of Zen build, almost all parts like original, except power supply transistor is bd239. Volume pot is 5Kohm, pot wiring is checked (output + in pot wiper). Tried different transformers, voltages were ~60V but also tried over and under voltages. Bias set 30ma. All parts stays pretty cool, under 40 degrees celcius.

Symptom is that at very low volume sound is little too much bass heavy. If volume is rised, then bass will become muffled and treble dives.

I have tried without 10uf output capacitor, same problem.


Power amp is Mofo build and it works with diy opamp preamp with 10db gain. BOZ can't get nowhere near.

You said you have it biased at 30 ma but the design calls for using a bias of
40 ma. I believe Nelson made some comment like " although it's not always
the case in this circuite the mosfet likes to be biased rather high " Ok I know
those arn't his exact words but it was something like that.
Joined 2010
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The output impedance of the BOZ may be in the neighbourhood of 1k ohm or more and I believe the MoFo has high input capacitance which would result in a treble roll-off.

The MoFo, being a source follower, has no voltage gain so it needs a high amplitude input signal to drive it to high power output. You need to check whether the BoZ can provide the necessary gain and swing to drive the MoFo.