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Hi.
I have one of the above bass amps. It's in excellent condition - barely marked - and also works really well. Except there's an intrusive hum...
With no input (nothing plugged in - I understand the input socket 'shorts' when not in use), there is an audible, low-toned, hum even on minimum volume. With the volume turned up to max, it's very audible indeed. Obviously turning up the bass control adds to it, as does pressing the 'mid-shift' control.
With a guitar plugged in, there's an additional, higher-pitched hum which is clearly now being picked up by the guitar itself - touching the metal bridge, for example, reduces it considerably. However, with the guitar's volume turned down to zero, the original hum is still there too.
I'm fairly au-fait with a soldering iron, and also have a decent knowledge of what all the components do. As a start, I've had a good search for dry joints, with no luck. I have also replaced the 2 power supply smoothing caps with new ones of identical value - no improvement whatsoever.
I've checked that the earth terminal of the mains supply is making good contact with the amp chassis, input socket 'earth' and everything else I think it should be. No luck.
I'm in the UK, by the way, just in case mains-power conditions are different to wherever this forum is based - I'm guessing the good ol' US of A?
There's a schematic available here: http://hpbimg.someinfos.de/diy/allge...-boxers-98.pdf . Although my model has '98 date written on the PCB, it has only 4 pots - bass, mid, treb, and vol whereas it suggest in the above manual that there's a newer 5-pot version for this year. Ho hum.
I'd really appreciate some thoughts on what to target next. Are there any obvious causes I should be looking at? I can replace any components no problem - I've had years of soldering practice - I just need to know where to 'go'...
Many thanks!
I have one of the above bass amps. It's in excellent condition - barely marked - and also works really well. Except there's an intrusive hum...
With no input (nothing plugged in - I understand the input socket 'shorts' when not in use), there is an audible, low-toned, hum even on minimum volume. With the volume turned up to max, it's very audible indeed. Obviously turning up the bass control adds to it, as does pressing the 'mid-shift' control.
With a guitar plugged in, there's an additional, higher-pitched hum which is clearly now being picked up by the guitar itself - touching the metal bridge, for example, reduces it considerably. However, with the guitar's volume turned down to zero, the original hum is still there too.
I'm fairly au-fait with a soldering iron, and also have a decent knowledge of what all the components do. As a start, I've had a good search for dry joints, with no luck. I have also replaced the 2 power supply smoothing caps with new ones of identical value - no improvement whatsoever.
I've checked that the earth terminal of the mains supply is making good contact with the amp chassis, input socket 'earth' and everything else I think it should be. No luck.
I'm in the UK, by the way, just in case mains-power conditions are different to wherever this forum is based - I'm guessing the good ol' US of A?
There's a schematic available here: http://hpbimg.someinfos.de/diy/allge...-boxers-98.pdf . Although my model has '98 date written on the PCB, it has only 4 pots - bass, mid, treb, and vol whereas it suggest in the above manual that there's a newer 5-pot version for this year. Ho hum.
I'd really appreciate some thoughts on what to target next. Are there any obvious causes I should be looking at? I can replace any components no problem - I've had years of soldering practice - I just need to know where to 'go'...
Many thanks!
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