Power amp under development

Thanks for responses. My preamp is actually in the same chassis as the amp (it is a bass amp), and actually disconnecting ground wires from PS to preamp and from preamp output to amp input reduced hum a lot. Their grounds are now connected through chassis, by in/out jacks only. I will try to put isolated jack for speaker output, to see what happens. I don't have a ground lift there, so maybe that is a problem?