Fishman Loudbox Artist

[drewl]

Anyone come across a schematic for one of these?
It seems to be quite different from what loudbox schems are around.

Channel one barely amplifying, and of course it's laid out much different than channel 2 which works.

I'm pretty sure it's got a bad LM339 comparitor, the only surface mount one I could find was a pull from a blown up power supply.

thanks.

[vintagekiki]

Loudbox 001 SM.pdf
https://www.diyaudio.com/forums/instruments-and-amps/300194-fishman-loudbox-schematic-share.html
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[drewl]

Yeah, I have that one, it's totally different.
Thanks.

This has two different preamp boards mounted together making it a pain to troubleshoot.

You have to take it all apart and balance it on top of the cabinet to connect to the transformer.

[drewl]

FWIW it was a bad comparitor.

Good channel - signal goes in, comes out bigger.
Bad channel - signal goes in comes out smaller.

half the resistors have no markings on them, also making it harder to compare channels for troubleshooting.

[Jazz P Bass]

Yeah.
I had one with a bad quad opamp.

And what a treat they are to work on with the guts all hanging out.

And that crappy crepe paper tolex?

They do sound good when they work.

[craigslist]

Hi Drewl, Which LM339 was it on yours... U3 by the output amp?

[Petr]

Yep, U3 (LM339 comparator) also in my case. CH2 not working. A bit tough working on it without a schematic. They luckily marked ICs according to the signal flow, I guess... (U1, U2, U3...)

[Mars Amp Repair]

Hello,
Not certain if this model falls into this known issue, but thought I'd throw it in here just the same. A bunch of the Fishman Loudbox amps have issues with metal filings in the pots that create all kinds of weird symptoms. Fishman will actually tell you this, too. BTW, they are very accessible for information and probably schematics, too.
You have to actually just blow out the pots with compressed air BEFORE you spray DeOx in them in order to not get the metal filings to just stick in there.
I've done this many times it will fix the weird issues. You can also measure from the pins of the pots to ground (or their case) to see if there is low resistance there just to perhaps prove this out before you blow them out.
Glen

[drewl]

Yes they do Mars!
Just had one in recently with that (and another ) problem.

Forgot about it at first then remembered!