Lab Series L5 crappy sound

[Randall]

Hoo Boy, I sure am going to need help with this one. Complaint is it breaks up like a fart when you lean on it. Customer changed out the speakers, so we know it's not that, but it sounds like it could have been. I don't even know where to begin on this one. Any guidance would be highly appreciated.

It's an L5 model 308A

http://www.rru.com/~meo/Guitar/Amps/...L11_scheme.pdf

[xtian]

It has an FX loop, so divide and conquer.

[glebert]

It has an FX loop, so divide and conquer.

Agree. I would also check the voltage rails for the op amps and the power amp.

[vintagekiki]

Check voltage at Speaker Output (J5); The voltage must be 0 VDC
Is it crappy sound on both channels or just one?
First test the PA, put the guitar in the power amp in (J6).
If the clear sound the fault is in the preamp.
Check voltage at pin1 and pin 7 of IC (4558)
Check voltage at pin6 IC (LF356; 741; 3080)

[Randall]

Well, after testing with the FX send/returns, and not being sure of the results, the issue has resolved. It appears to have been the return jack. I gave it a good cleaning, but it still makes a loud pop when plugged into. I have repaired many problems with return jacks, but this one sounded unique to me. The amp still sounds lousy to my ears, but I have never experienced one of these before, so maybe it is just a not so great sounding amp?

At any rate, I want it gone.

[Leo_Gnardo]

The amp still sounds lousy to my ears, but I have never experienced one of these before, so maybe it is just a not so great sounding amp?

Back when they were new, no less than BB King was a fan. At least that's what the gee-tar magazines would have you think. He appeared in print ads for Lab Series, so you expect he was at least familiar with them and approved of them. And probably got a free amp or 2 or 3 for his effort. Did anyone see BB playing live with one? I've seen him with his old standby Fender Twin, original not reissue blackface only please.

In more recent times Ty Tabor of King's X has been using a Lab as one of his secret weapons. Well the "secret" got out some years ago, since then there's been a minor resurgence in the Lab Series popularity.

Here's an article, a little snooping will find you more:

https://www.guitarworld.com/gear/the...net-by-kings-x

One of the Lab features is an EQ section designed by Robert Moog, with a very versatile midrange section. This alone might be enough to flummox some guitarists, otoh it can be an unbeatable asset for those who learn to use it.