RGR Model 4 Pre Amp ....HUM QUESTION

When RGR Pre- Amp tone button is pressed IN, this Unit is quiet / NO HUM.

However, when tone button is OUT, I get a HUM.

The hum disappears when pressed IN.

Any thoughts about this problem ?

Thanks

rocky131304-27-2022 1:40am

fiesta75 Details Discussions Posts This discussion Message User 1,378 posts 04-27-2022 at 02:39am Copy Comment URL Report Comment Edit Delete How long have you had this preamp? Have you made any power amplifier or other changes? These are fairly old and have been known to have some cold solder issues.