What the FANKUS is this Wolf Amplification 20w Bass amp

[Bruce / Mission Amps]

Wolf Amplification 20w Bass amp (2x10) combo... what piece of work... total crap.

Doing a favor for a friend and it is kicking my ass.
His kid blew it up and they aren't very well to do... so... you guys know the drill.
How hard could a single 4558 and a 20-30 watt LM1875t power chip be?
Anyone even heard of this thing?
I get nothing from the 4558... voltages look OK... nothing with a new 4558 installed either.
The power chip LM1875t isn't anything special ... voltages look high 28vdc, but OK yet with a 500mvac signal on the input... nada... output.
I'm gonna being throwing it in the trash here pretty soon and buy them a new polished turd from the Guitar Center and save myself a headache.

[Mark Hammer]

Let me guess. Volume, treble/middle/bass, headphone output and distortion switch?

4558/LM1875 amplifiers (and their close cousin, the TDA2030/2040/2050 power amplifier stage) are a bit like 12AX7/6V6/5Y3 amps in that there is really a limited number of permutations and combinations. They all share a lot in common. I don't have a schematic for the one you note but I would imagine just about any LM1875-based amp with a 10" speaker (marshall? Crate? Fender? Ibanez?) would be very very close.

[Enzo]

If there is no signal leaving the 4558, put one there. Does probing the output pins on the 4558 make any noise out the speaker? Does probing the input pin of the amp IC? If there is no DC on those places, flip your meter to ohms or diode. That will put a little voltage on the probes. Touch that to the signal path and a working stage makes a pop sound.

In a working circuit, you can;t measure or scope signal at the op amp input pins, but pull the IC, and now signal should be there. if it isn;t getting there without the IC, it won;t magically appear when the chip is installed, Thinking perhaps the cap from the input jack might be busted or something.

[J M Fahey]

Hi Bruce..
Please don't junk it so quickly.
Of course your time is worth more than the replacement cost,that's why Fender and so many others have those "do not repair" amp lists, but take it as some mental excercise or an unexpected trip into the SS badlands.
Lacking schematic trace it backwards, that's to say check speaker first, run backwards to the power chip out pin, then to its signal in and so on.
You know the drill, in fact you could *write* the service manual.
Your trusty old finger will provide all the signal you'll ever need .
Good luck.

[imaradiostar]

I've ended up with a few like that over the years- solid state amps that aren't worth repairing but even if they were they don't sound fabulous. I keep them around as a ready-made chassis to try little low-wattage tube designs with leftover and junk tube amp parts.

It's the old "what can I build with this?" game...which of course is no help when it comes to making money. Sorry it's being difficult.

jamie

[Bruce / Mission Amps]

Yeah after putting in a new 4558, I stuck a TDA2040 in and I do get some sound but not like 10 or 15 watts.
Signal to the 4558 input is OK.... and I can see clean signal on the scope coming out but it isn't really any more then going in. That should be a clue but I don't know what.
When I said I can feed 500mvac in the amp I meant the PA chip... still hardly
anything over a watt or two or three.
I don't do much SS repairs anymore but doing one with out a schematic is really awful.
I tried to explain this thing isn't worth my trouble to figure out but it's oh please please... I'm serious, a broken SS VOX Pathfinder chassis shoved into this cabinet would probably be cheaper and easier.

[J M Fahey]

Hi Bruce. Doesn´t one of your regular clients have some similar (working) amp collecting dust?
Maybe you could get it for nothing or in exchange for some small service which will certainly waste less of your time than repairing it, and make your young poor client happy.
I also have my own share of "please, please" customers , like most others here, I guess.