Maestro phaser has DC thump sound, I think it's the power supply

[gutsofgold]

I was gifted two Maestro PS-1A phasers, both broken for different reasons. I went through and recapped both of them because these pedals have internal power supplies, crude zener regulators. After powering them on, they both phase fairly well, but on both units whenever the LFO driving the JFET gates reaches about -2VDC the sound cuts out and I get a bad DC thump. I took one of the phasers and disconnected it's internal power supply and ran a bench top +12V and -12V supply to it and this cures issue completely. I have a theory as to what might be going on but I can't quite prove it. Here is power supply schematic...



If I move those 470uF capacitors to the other side of the 270ohm resistors, it cures the problem. Which leads me to believe the JFETs enter some state that causes current draw and the transformer can't handle the demand which causes the output at transformer to sag and this causes excessive current through those quite large 470uF caps. If they are on the other side of the resistor there is some current limiting occuring between transformer and big caps. Could this be correct?

[duck_arse]

what are the measured supply voltages when using the mains supply and it is thumping? you need the 470uF's to smooth the raw rectified DC, you might well need additional caps downstream of the 270R resistors. but there may be something else causing the problem, like a bad cap or zener.