My C120a pre-amp has developed a mains hum in only one channel.
Pressing the tone bypass switch eliminates the problem. Adjusting the bass control knob seems to affect it more greatly than the treble control too.
Any suggestions for areas to check, components to replace?
Pressing the tone bypass switch eliminates the problem. Adjusting the bass control knob seems to affect it more greatly than the treble control too.
Any suggestions for areas to check, components to replace?
Sounds like you're in the right part of the circuit.
I just debugged multiple mains hums in an amp I was building; each time I fixed it it was due to my poor (but improving) soldering skills. My takeaway is a hum is a grounding problem which is a loose part / connection gone bad.
I just debugged multiple mains hums in an amp I was building; each time I fixed it it was due to my poor (but improving) soldering skills. My takeaway is a hum is a grounding problem which is a loose part / connection gone bad.
Interestingly, the hum is NOT affected at all by the output volume control or balance.....so it seems to be caused by the tone control section, BUT impacting the signal AFTER the volume/balance controls......
Yes, the tone section is electrically after the volume control in this unit.
The problem should be in the tone circuit, since the power supply is shared.
Likely a bad solder joint or connection. Tap around that area very gently
with a pencil eraser or other insulated object to see if the noise is affected.
Luxman C-120A Stereo Duo-Beta Preamplifier Manual | HiFi Engine
The problem should be in the tone circuit, since the power supply is shared.
Likely a bad solder joint or connection. Tap around that area very gently
with a pencil eraser or other insulated object to see if the noise is affected.
Luxman C-120A Stereo Duo-Beta Preamplifier Manual | HiFi Engine
Last edited: