Thomasdj
Member level 5
Hi,
I am building a 3ch 100w high gain guitar amp and I'm almost there..I think
All three channels has great sound and all the tone stacks works well.
Channel 1 is working perfectly..no hum at all!
Channel 2/3 got a 100hz hum..
The hum increase a bit when i turn the bass past 0.5 and change shape with the rest of the EQ..the hum also rise with the master volume..If I ground the grid of V2b (see schematic) the hum disappers and the amp is totally quiet.. If I ground the grid of V2a the hum increase and becomes "more square" sounding.. so my guess was that it could have something to do with the 15uf cathode cap at V2a which is switched in/out by RY1'a..I've tried to replace the 15uf cap and changing it to a lower value, but the hum still remain the same...it the same issue with both channels 2/3..
I don't think it's the input grid at v2a since it's shared with channel 1..which is quiet..
The hum is not affected by the gain pots at all..
The humming decrease a bit when the negative feedback is connected..but not much
Any suggestions how to solve this issue?
btw..All my voltage are close to the shown in the schematic..My PT has center tapped fillament (grounded at 220uf cap)..the heaters are tight twisted and runs underneath the pots and along the chassis' sides. I've tried swapping tubes..
Thanks
Best regards
Thomas
I am building a 3ch 100w high gain guitar amp and I'm almost there..I think
All three channels has great sound and all the tone stacks works well.
Channel 1 is working perfectly..no hum at all!
Channel 2/3 got a 100hz hum..
The hum increase a bit when i turn the bass past 0.5 and change shape with the rest of the EQ..the hum also rise with the master volume..If I ground the grid of V2b (see schematic) the hum disappers and the amp is totally quiet.. If I ground the grid of V2a the hum increase and becomes "more square" sounding.. so my guess was that it could have something to do with the 15uf cathode cap at V2a which is switched in/out by RY1'a..I've tried to replace the 15uf cap and changing it to a lower value, but the hum still remain the same...it the same issue with both channels 2/3..
I don't think it's the input grid at v2a since it's shared with channel 1..which is quiet..
The hum is not affected by the gain pots at all..
The humming decrease a bit when the negative feedback is connected..but not much
Any suggestions how to solve this issue?
btw..All my voltage are close to the shown in the schematic..My PT has center tapped fillament (grounded at 220uf cap)..the heaters are tight twisted and runs underneath the pots and along the chassis' sides. I've tried swapping tubes..
Thanks
Best regards
Thomas