Fishman Loudbox Performer
Hi folks…I’m trying to help a friend with his Fishman Loudbox Performer amplifier. It’s a great bit of kit, with a wonderful sound. Sadly it has a low level 100Hz hum, which is twice the UK mains frequency.
I really need a circuit diagram, or schematic diagram if you are in the United States.
The amp appears to work perfectly apart from this hum. There are no dry joints on any of the circuit boards, nor are there any earthing faults.
Being at 100Hz, the hum is coming from the rectified DC, i.e. after the bridge rectifier. I’ve checked the bridge rectifier diodes and all is well. I’ve actually replaced the three main smoothing capacitors…which made no difference.
I’ve checked all the voltage regulators and everything seems fine, and I’ve also checked the DC feeds on the ribbon cable to the preamplifier…all is well. Even on maximum sensitivity, I can’t see any 100Hz ripple on the supply lines!
The master volume control varies the level of the hum, right down to zero when It’s anticlockwise. All the controls on both channels on the preamplifier vary the level or tone of the hum, right back to the input level controls.
Even at a very low level, I’d expect to be able to see the 100Hz hum / ripple on one or more of the DC supply lines, but there is nothing.
Can anyone offer any suggestions or help with a diagram please?
There are no Fishman repairers I can find in the UK.