RGR Model 4 Pre Amp ....HUM QUESTION

I too have the same hum problem with my RGR 4. It is only on the right channel. For awhile I have been plagued by a right channel hum coming from my Sumo Andromeda amp. I was resigned to replacing one or both power supply caps. After reading your post I tried the RGR 4's tone button. Voila, pushed it in and hum GONE! That's a lot of worry gone! I really like the Andromeda with the DCM Time Windows and will continue to use it! The RGR 4 also sounds fine - as long as I leave the tone button pushed in! 

@rocky1313 : Thanks for your post! Otherwise I would have done an unnecessary cap job on the Andromeda amp - and still had the right channel hum problem!

Tone button IN means the tone control circuit is engaged. Just leave it IN to eliminate hum. Probably just a quirk of some of the RGR 4’s. Any other owners notice the same thing? My first RGR 4 back in 1980 was hum-free for all its life (20+ years). No.2 bought five years ago has the right channel hum problem with tone circuit OUT. 

The RGR 4 was in 1980 a giant-killer preamp designed by Robert Grodinski of pro-audio RG Dynamics fame. Sonically as good as - or better! - than the then- current champ - the $4500 Levinson ML7. So for $650 one could buy a SS preamp in the same sonic class as the Levinson.