Double Bass GK 200MB hums when turned off

[gerry grable]

Excellent idea! Anyone thinking of doing this should keep in mind the stock power switch is likely rated for 12 volts or a similarly low voltage. Modifying the wiring to make the switch break the incoming wall current would require using a switch rated for at least 120 volts.

I guess it's up to the individual, but I think it's a lot of trouble (have you seen how crowded the components and circuit boads are in that amp?) and expense to go through when all you have to do is unplug it or use a powerstrip. Also, it's only audible in a very quiet room and unnoticeable in a playing situation. Believe me, that "excellent idea" above is a lot more difficult than it sounds.

 

[gerry grable]

I owned both versions of the 200MB. I do remember that hum, especially in certain rooms I used to gig in. I recently purchased a 200RCB, the head only version of the 200MB. Because they had to move the transformer up into a single case with th Pre Amp and Power Section, the black case it's housed in is pretty large, especially when compared to the little sliver MB 200, which is a totally different amplifier. The 200MB/RCB preamp section had one of the finest voicings ever for Double Bass, IMHO.

Ric

I know nothing about these little silver amps you show in this post, but your description of the 200MB/RCB sounds interesting

 

[David Jayne]

The power switch is on the secondary of the transformer. 43 volts there- they probably did it that way so they could use a smaller switch. If you can find a way to squeeze a bigger one in there, there's no real reason you couldn't switch the primary instead. But I suspect there isn't room.

 

[Demon_Hunter]

I've had one since 1987 and it's always done that.
I just always unplugged when done playing, didn't think anything else about it until now.

 

[tgorycki]

Yeah it probably would be easier just to unplug the amp then modify it, but while I have mine apart for renovations...

On second thought, probably not a good idea running 120 volts to the switch on the circuit board, especially since there's little room for the wires from the cabinet.

I found this interesting and inexpensive power cord receptacle/fuse holder/power switch combo that would make for a nice upgrade. However, be sure to silicon seal the heck out of it!

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[johnhoef]

Something that has not yet been mentioned here, so I will contribute. The back panel where the transformer is mounted may have a resonant frequency of around 60hz. Thus, the vibration of the transformer is enhanced simply by it being mounted to that back panel. I suggest mounting it to the bottom panel. The bottom panel is much smaller, thus a higher resonant frequency. Further, if any of you do this, use rubber grommets to mount the transformer to further reduce transmission of vibrations. I bet this will, if not fix the problem, reduce it substantially. If any of you try this, please do report back to us.