Markbass amp low volume

[tatthecant]

Hello I have a Little Mark Tube 800, the volume is really low have checked all the obvious leads etc, taken it to my repair guy who is usually quite good, but he says he can't find what's wrong with it, has anyone had similar issues?, was it something simple ,an easy fix? or is the amp F****d, Cheers

[MoonBassAlpha]

Have you tried bypassing the preamp section,  plugging straight into the effects return? I'm thinking the valvein the preamp is a likely candidate.  Did your tech try swapping it out? 

[tatthecant]

Not sure what he did , but I've used him for a few years now and he is pretty good, I think he probs did try valve as it's quite an obvious thing, but I'll try going through effects return later and let you know if it works, thanks 

[BassBunny]

I had exactly the same problem with an SA450. I ended up selling it cheap as a " half output" job.

The alternative is to send it to Real Electronics in Sheffield who are the Mark Bass official repairers. The problem is that it would cost more to repair than it is worth. MB won't release the circuit diagrams and Real just swap circuit boards.

 

Edited December 27, 2020 by BassBunny

[BassBunny]

Just remembered an email I got from @johnny2shoes who managed to get his LM3 fixed by someone in Bolton. Might be worth messaging him.

I'm pretty sure his was a Class A/B one, same as the SA450, rather than a ClassD, which most tech's won't touch.

[ikay]

I found an LM Tube 800 circuit diagram here if that's of any use - https://el34world.com/charts/Schematics/files/_miscellaneous/Little_mark_tube800_sm.pdf

[Jakester]

I’ve just had my Combo Amp II (the combo equivalent of the LMIII) back from Real Electronics for similar issues. 
 

They tested it fully and couldn’t find anything wrong - the only thing they could suggest was a dodgy pot so they replaced all of the control pots - might be worth getting that done?

[tatthecant]

Hello , I've tried bypassing preamp into effects return, no different ?