Yamaha T50C Soldano Overdrive Hum

[kdawg]

Hello - I have a Yamaha T50C Soldano that was just re-tubed. Both channels work fine, but the hum/noise floor on the overdrive channel is way too high. Filter caps have not been replaced.

I checked all resistors since there was another thread about some V5 resistor burning out, didn't see any problems. I tried flipping tubes around, no real difference. The hum seems to be starting at V2 and I don't know if its just amplifying the noise floor/hum so much more than the clean channel that its a problem.

I am measuring 3VAC right off the standby switch, is that a sign the filtering is not enough? It's definitely preamp stage as I can plug into effects return and its quiet as could be.

btw - happens with or without anything plugged in to the input jack.

Schematic:
http://www.freeinfosociety.com/elect.../yamahat50.pdf
Thanks
-kdawg

[Chuck H]

Well, get the hum going the way it offends you and then unplug the instrument cable from the amps input. Hum stop? If yes then the amp IS amplifying noise as well as signal that is ALL coming from your guitar and there's not much to be done short of better shielding for your guitar and maybe a noise gate. If no then there should be something that can be done circuit wise to reduce the hum.

There are different kinds of noise that manifest in high gain circuits. Hiss and hum are the most common and pronounced. Hiss is a byproduct of gain. Not much to be done about it in an existing design. Hum can often be corrected if it's a circuit issue and not from an outside source let in through the input. Also, if it's a ground issue and the amp is on a PCB (which your amp is) possibilities are more limited.

[Gtr_tech]

These amps were supposedly better built than the "real" Soldano version. They used shielded cabling in sensitive areas to reduce hum pickup. High gain amps are more apt to have hum/noise issues just because they run so many gain stages in series. But it shouldn't be obnoxious....

I had a customer call me about bringing one of these in for some work. When/if it arrives I may be able to shed more light on your problem.