radardoug said:
The fact that you assume it is the power supply would indicate you are not very knowledgable about electronics.
Noise after a period of warmup would normally indicate a thermal condition.
nielsk said:
Bad transistors in the audio path are common on these, fire it up on the bench, get it to make the noise and work your way back from the output.
Normally bad filter caps will provide some nice low end hum, not hissy white noise.
hissy white "noise normally" can be caused by bad transistors or colder solder joints/bad contacts/bad pcb tracings.
If it only does that after being on for a while it's probably a thermal condition, and can be caused by bad transistors or colder solder joints/bad contacts/bad pcb tracings that will change their condition while warm/hot.
Do you have a signal probe?
if not you should build one, it's easy enough:
http://diy-fever.com/misc/audio-probe/
http://www.geofex.com/FX_images/audioprb.gif
http://www.diystompboxes.com/pedals/debug.html
nielsk said:
fire it up on the bench, get it to make the noise and work your way back from the output.
Do what Nielsk said with the probe.
I always probe circuits from the input, following the schematic and stop when the noise appears, then I know it's in that component or that part of the circuit.
Most of the places and people advise working from the Output to the input, Whatever what works for you.
Maybe when some piece of equipment has no output sound is better to work from the output to the input, but in this case you want to listen to the clean sound all the way until it changes for Hissy, so from input is better.
Feed the 240 some slow as percussive music so you can always hear the reverb.
I hate feeding 1K signal for probbing, It will be boring and give you headaches, music is much nicier for a probing job
