SOZ dc offset voes persist

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psarin

Member
2001-11-09 6:35 am
Mars
i have completed my SOZ, and initial results with Dynaco PAS-3X preamp, driving a pair of RS 40-1354A's in open baffles are EXTREMELY promising ;) 13.5VDC rails and i have MORE output power than i know what to do with!

however, the annoying problem with the high DC offset still persists. after everything has nicely warmed up, with inputs and outputs terminated properly, i'm still seeing about 200mV dc offset at the speakers. i've gone through sampling ALL(~12) of my MOSFETs, and V_gs differences in the installed circuit between a pair are at the ~ 0.01V level (a typical pair has V_gs=4.06 and 4.07V).

as built, my amplifier has IRF540's, the input impedance is R10=600K to keep the PAS-3x happy (Q2 gate is grounded to RCA input pins outer shield, keeping it separate from the power-supply gnd).
the preamp by itself has a small DC offset of <10mV at each output. i'll be trying various values of R10 to see the trade-off between low-freq response and high-freq distortion.

i'd be grateful for any advice/opinions
-pradeep
 
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