Longtime reader - I've looked around quite a bit but i cant seem to find this problem.
My grounded grid pre has a ghost infestation all of a sudden. It stopped working for no apparent reason (no part of the system was changed), and i discovered this: For some reason, if i ground the PCB, it stops passing audio.
I had a star grounding centered on the PCB so that the mains earth, - from each rca, and the PCB GND were terminated at one point and it worked great for a year+.
Now, if either the mains earth or the - from the RCAs touch any part of the GND on the pcb, the thing stops passing audio. It becomes silent, though the tubes are still lit.
Since there is no GND to the PCB there is a hum, though the circuit still passes audio. The hum starts when the unit is plugged in and gets worse when it is turned on.
The wierd bit is this is only sometimes! it mysteriously stops, then its ok, then it works for a week, then today, if it's grounded it won't pass signal. Normally if the ground becomes connected it will increase slightly in volume and the hum will disappear.
I have tried: rewiring the whole unit, changing the tubes, eliminating all extraneous components so there is only the PSU and in and out from the pcb connected directly to RCA, plus the grounding changes above.
Is there something I'm missing?
My grounded grid pre has a ghost infestation all of a sudden. It stopped working for no apparent reason (no part of the system was changed), and i discovered this: For some reason, if i ground the PCB, it stops passing audio.
I had a star grounding centered on the PCB so that the mains earth, - from each rca, and the PCB GND were terminated at one point and it worked great for a year+.
Now, if either the mains earth or the - from the RCAs touch any part of the GND on the pcb, the thing stops passing audio. It becomes silent, though the tubes are still lit.
Since there is no GND to the PCB there is a hum, though the circuit still passes audio. The hum starts when the unit is plugged in and gets worse when it is turned on.
The wierd bit is this is only sometimes! it mysteriously stops, then its ok, then it works for a week, then today, if it's grounded it won't pass signal. Normally if the ground becomes connected it will increase slightly in volume and the hum will disappear.
I have tried: rewiring the whole unit, changing the tubes, eliminating all extraneous components so there is only the PSU and in and out from the pcb connected directly to RCA, plus the grounding changes above.
Is there something I'm missing?