Hello guys,
Please feel free to move this thread if this is not the correct place,
I have been asked by a friend to check his SPL Goldmike preamp which he accidentally overvolted by changing the voltage settings... he blew the fuse so the overvoltage was not long, but there are issues...
Everything seems OK (voltages are correct) but there is a heap of noise and a lack of gain... I guess the temporary overvoltage did not pass through the solid state regulators (classic 7812/7912/LM317 phantom) so the low voltage circuitry should be fine, but I have some doubt about this, signal on first stage (mic preamp) seems nice enough so I think this part is OK...
It could also be the input zeners which saw a big overvoltage and are now producing more noise than input has signal, but it doesn't explain gain loss...
Would the high voltage part be damaged from the overvoltage during such a short time as a fuse blowing? It should be around 700V during a couple hundred milliseconds, would it be enough to damage the 12AX7 from the valve stage? (this is in combination with a SSM2017 or SSM2019)
I'm in the process of trying to get the schematics, found it on GroupDiy but the archive is not existing anymore and I'm waiting account activation to be able to contact the original poster...
Anyone would have some idea to point me in the right direction? The friend in question is a music artist and as anyone would guess the funds are not good these times with no events, so I'm dedicated to find a solution and help him not to spend on another preamp... (even if there is way better than this model)
Please feel free to move this thread if this is not the correct place,
I have been asked by a friend to check his SPL Goldmike preamp which he accidentally overvolted by changing the voltage settings... he blew the fuse so the overvoltage was not long, but there are issues...
Everything seems OK (voltages are correct) but there is a heap of noise and a lack of gain... I guess the temporary overvoltage did not pass through the solid state regulators (classic 7812/7912/LM317 phantom) so the low voltage circuitry should be fine, but I have some doubt about this, signal on first stage (mic preamp) seems nice enough so I think this part is OK...
It could also be the input zeners which saw a big overvoltage and are now producing more noise than input has signal, but it doesn't explain gain loss...
Would the high voltage part be damaged from the overvoltage during such a short time as a fuse blowing? It should be around 700V during a couple hundred milliseconds, would it be enough to damage the 12AX7 from the valve stage? (this is in combination with a SSM2017 or SSM2019)
I'm in the process of trying to get the schematics, found it on GroupDiy but the archive is not existing anymore and I'm waiting account activation to be able to contact the original poster...
Anyone would have some idea to point me in the right direction? The friend in question is a music artist and as anyone would guess the funds are not good these times with no events, so I'm dedicated to find a solution and help him not to spend on another preamp... (even if there is way better than this model)