Solid State Guitar Amp Forum | DIY Guitar Amplifiers

Hi friends; A very long time away so apologies. I did a quick cleanup on this Randall RG75D model SS amp. Built in China with one 12" spkr. This amp is almost silent at idle but start playing thru it and it sounds poor with some kind of high freq noise on every note. I checked the speaker wires and there is .25 vdc on them at idle. Is that enough dc to cause a problem? thanks amigos

Quote from: smackoj on July 15, 2025, 04:35:58 PMHi friends; A very long time away so apologies. I did a quick cleanup on this Randall RG75D model SS amp. Built in China with one 12" spkr. This amp is almost silent at idle but start playing thru it and it sounds poor with some kind of high freq noise on every note. I checked the speaker wires and there is .25 vdc on them at idle. Is that enough dc to cause a problem? thanks amigos

Not by itself.

Disconnect those speaker spade terminals and try the amp with another speaker or cabinet.

Also connect another amp to the internal speaker.

So we know whether it´s an amp or speaker problem.

Hi and thank you; I did try a diff spkr and the sound seemed slightly better but not great.I tried changing tone settings and found improvement in the Clean Ch. The OD channel still sounds below par. May be the quality of the ICs on the separate pcb for the Digital Effects?

Do you think this is how it sounded when new?  Doesn't the clean channel also use the FX board?

I have heard high frequency like that on those small portable Yamaha digital amps. Perhaps something to step up to high voltage but low current.

I don't think this is the case but I remember playing around with led strips that put out a high pitch noise. To make it worse the person using these led strips was putting them as guides on their guitars fret board. The power source has to be put somewhere where it won't pick up the frequency. But that Yamaha modeling amp put out this constant noise and it sounds similar to the high voltage/low amperage led strips. They use DC batteries to invert back to AC which stepped up to 100v. Maybe that Yamaha modeling amp didn't have a little noise gate to get rid of the high pitch when idle? Perhaps your amp has a gate? I would clean up the pots and switches as well. Justin Case.

Hi and thanks; I replaced the speaker, cleaned everything I could get to without pulling the boards out. The noise still remains. The rest of the amp functions are working and it will get very loud but it's ear piercing at high volume.I wonder if it would be OK to try a transformer after the amp output chips? I know Peavey used them on some of their SS amps?

No. Period.


Please post a YT video showing us what you call noise, we have no clue what that word means.