I have a hum in the left channel of my Counteroint SA-1000 preamp. now before I start I have tried all the tricks to narrow it down with no great success. I fully upgraded this preamp a few years ago and was in heaven with the sound. Until....it slowly developed a hum in the left channel after 8 months of no hum issues and which I thought was a tube going bad. so I changed it, same hum.
now the question is is it a 60hz or 120hz hum? I would love to tell you but my scope is down and the 2 dmm i have one doesn't have a freq measurement and the other that does for some reason is not picking up the hum.
I did the chop stick trick and resolder all solder joint again but not all at the same time.
i have replaced and upgraded all components in the filament, B+ supply active and passive components plus check all the grounds. even replace all the components in the relay circuit. All the B+ caps have been replaced and upgraded to Mundorf Tube cap and Mundorf HV MLAL caps. replaced all active comeponents, Mosfets, Zener diode, regulators twice just to make sure.
All film cap were upgraded to Auricaps (and replaced coupling caps in the linestage again with Dynamic caps), all resistors around the tube have been upgraded to Mills or Caddock MK-132. all tube sockect were up graded to ceramic gold plated. Volume and balane controls were upgraded to TKD, all wire and connectors were upgraded to vampire. upgraded tranny to the plitron for this preamp from altavista audio.
So here's what I did and what the results were. I shorted the signal to ground before the volume control...no change in hum. Shorted the signal after the output coupling cap hum was gone. so it seem like the hum is definitely between those 2 stages of the tube and mosfet. I did do the same in the phono section but no change in hum. this hum originally doesn't change in volume when you turn volume up. Always the same. Now it sounds to me like a 60hz hum cause it seems at the same freq, as the fridge whe it running which give off a 60hz hum noise.
I did find a 200k resistor on the left channel that measured 210k. replaced both 200k resistors in both channels no change in hum.
all the wires from the tranny are twisted now and no change in hum. I'm going to hit all the solder joint one last time before i through this preamp out the window but take out all the parts before I do that!
and i will also solder the grounds from the RCA screw ground point to the ground wire connected to the ground spacer rings that are screwed down for ground on the connectors just to make sure.
Any help would be greatly appreciated.
Thanks
now the question is is it a 60hz or 120hz hum? I would love to tell you but my scope is down and the 2 dmm i have one doesn't have a freq measurement and the other that does for some reason is not picking up the hum.
I did the chop stick trick and resolder all solder joint again but not all at the same time.
i have replaced and upgraded all components in the filament, B+ supply active and passive components plus check all the grounds. even replace all the components in the relay circuit. All the B+ caps have been replaced and upgraded to Mundorf Tube cap and Mundorf HV MLAL caps. replaced all active comeponents, Mosfets, Zener diode, regulators twice just to make sure.
All film cap were upgraded to Auricaps (and replaced coupling caps in the linestage again with Dynamic caps), all resistors around the tube have been upgraded to Mills or Caddock MK-132. all tube sockect were up graded to ceramic gold plated. Volume and balane controls were upgraded to TKD, all wire and connectors were upgraded to vampire. upgraded tranny to the plitron for this preamp from altavista audio.
So here's what I did and what the results were. I shorted the signal to ground before the volume control...no change in hum. Shorted the signal after the output coupling cap hum was gone. so it seem like the hum is definitely between those 2 stages of the tube and mosfet. I did do the same in the phono section but no change in hum. this hum originally doesn't change in volume when you turn volume up. Always the same. Now it sounds to me like a 60hz hum cause it seems at the same freq, as the fridge whe it running which give off a 60hz hum noise.
I did find a 200k resistor on the left channel that measured 210k. replaced both 200k resistors in both channels no change in hum.
all the wires from the tranny are twisted now and no change in hum. I'm going to hit all the solder joint one last time before i through this preamp out the window but take out all the parts before I do that!
and i will also solder the grounds from the RCA screw ground point to the ground wire connected to the ground spacer rings that are screwed down for ground on the connectors just to make sure.Any help would be greatly appreciated.
Thanks
