Low L2K output level... hopefully solved? Thoughts welcome

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Low L2K output level... hopefully solved? Thoughts welcome

Postby vibroverbus » Sun Aug 12, 2018 2:38 pm

After getting another couple of basses restored and 'back online' recently, I suddenly notice that my 'big boy' G&L seems to have very low output... 1997 L2K w/ v.1.0 pre-amp board.

It still sounded OK tone-wise but defintely low volume and not maybe as crisp and clear as I expected. Esp noticable when compared BTB to the other basses with exact same amp, same settings. This is pretty weird for what you'd expect for MFD's vs the other basses' singles (albeit hot singles I must say...) I of course replaced the battery for the pre-amp but that didn't seem to have big impact, and, it was pretty quiet in passive/bypass mode also/anyway.

Long story short did some diagnosis, removed the pre-amp board entirely and voila output seemed to come back... so...

Cleaned up all the solder connections to the pre-amp board, redid all the wires leading to and connections at, and, re-seated the Op-amp chip (which did seem to seat microscopically down into the socket more...) In the process discovered maybe the ground connection to the board was marginal (many broken strands at the solder joint end, only holding on by a thread). And after all that the volume and tone seems to be back up to snuff, but I'm still watching this one for any signs of issues..

I know in 'passive' mode the board wiring condition shouldn't have mattered but it sure seems like there was some parasitic drain of some sort impairing the signal level? None of the connections I redid should have made the slightest impact on passive mode, but if the op-amp does put some residual load onto the input then maybe that could assplain it...
Bass Stuff: 1997 G&L L-2000, 1964 Mosrite Ventures, 197? Epi ET-280, 1985 GK400RB, Kustom 1-15B w/ Delta 15A, 1966 Fender Blonde Piggyback Bassman w/ OE Jensens
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Re: Low L2K output level... hopefully solved? Thoughts welc

Postby Ken Baker » Sun Aug 12, 2018 3:49 pm

vibroverbus wrote:Cleaned up all the solder connections to the pre-amp board, redid all the wires leading to and connections at, and, re-seated the Op-amp chip (which did seem to seat microscopically down into the socket more...) In the process discovered maybe the ground connection to the board was marginal (many broken strands at the solder joint end, only holding on by a thread). And after all that the volume and tone seems to be back up to snuff, but I'm still watching this one for any signs of issues..


I would say you found your problem. Excellent work! Now that you have all the solder points cleaned up and in good shape, the only thing to watch out for is the jack. They're a known failure point, and failure can be hastened by using cheap import cables (which usually fit loose) and/or Monster cables (which usually fit too tight). Info on replacement is here.

I know in 'passive' mode the board wiring condition shouldn't have mattered but it sure seems like there was some parasitic drain of some sort impairing the signal level? None of the connections I redid should have made the slightest impact on passive mode, but if the op-amp does put some residual load onto the input then maybe that could assplain it...


Your failure kind of depends on where the dodgy ground connection was. The preamp's input is always in circuit; it's the output that gets switched. This means that in passive mode the preamp loads the circuit a tiny bit. If the bad ground was in an electrically centralized location you could have seen this effect.

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