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Marshall 5010 Needs Help

Started by El Scorcho, March 18, 2018, 09:32:21 AM

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El Scorcho

If you think there were clipping diodes in there originally, I would be interested in putting maybe a yellow Led on D1, and a pair of germanium diodes across D2 for more asymetrical clipping, but I don't want to start a fire if it's not for clipping.


Which backs up my thought that they are back to back feedback diodes across an op amp stage for clipping.  And they were later removed, either as a mod or as a production change.  I could be wrong.

El Scorcho

I got an e-mail back from Marshall. They won't give out a schematic, or even confirm there is an alternate version. If I want it returned to stock, I have to send it to them.


Quote from: El Scorcho on March 26, 2018, 12:58:38 PM
I got an e-mail back from Marshall. They won't give out a schematic, or even confirm there is an alternate version. If I want it returned to stock, I have to send it to them.

Does your Amp look like this?

If you can't find a schematic then take clear pictures of the inside,
Both sides of PCB if it's possible. :tu:

El Scorcho

Hi, Phil. Mine looks very similar, only the two input jacks are verticle, and there is no line out/headphone jack. I'm not at home, but will get some pics when I get back tomorrow.

El Scorcho

  I found a short video of one just like mine, with the same ugly crossover distortion. Funny, the horizontal and single input versions seem to all sound great.

Watch "Marshall Master Lead Combo - Fizzy Distortion" on YouTube


It would be fairly easy to adjust out the crossover distortion, probably just a resistor value change, but you would have to draw out the schematic for the power amp section as the newer schematic uses different components there.

As far as changing the amp back to "stock", it is probably closer to stock than you think.  There seem to be references to the older version as the "red mckenzie speaker" version.  If you could get in contact with someone who has one that would take some pictures of the circuit board, it wouldn't be too hard to figure out which components have been changed in your amp.


I listened to the video link, I can't help but note that most of these small SS marshall's had a lot of distortion because that is what the market dictated. Even some Valve marshall's added cross signal Back to back diodes for some earlier crunch/distortion. (same idea as D1&D2 in this amp)
The buyers wanted the distortion. ;)

I've looked over the PCB and it looks stock except that D1&D2 have been removed. This would actually remove some distortion and deliver a cleaner and bigger signal to the power stage,,,BUT as the power stage is a very basic design it may now be distorting even more so :-\ Hard to know cause I've never worked on these Amps. xP

I'm fairly sure;
You could tap into the Volume (VR2) with an MP3 player or other audio signal which bypasses the preamp and hear if the power stage is running clean. If it's clean then the problem maybe in the preamp.
The centre wiper of VR2 is the input to the power stage it connects to C5 which then runs up to the base of TR2.

I doubt this amp was ever capable of super clean so you may not be able to improve it much. 8|
Reinsert those missing diodes (D1&D2) and it would be stock.


C2 definitely looks suspicious.
Should probably be a small tantalum cap like C1 and C6.
Also it looks swollen.
Don't know if this would have anything to do with the distortion you are hearing,
but I'd replace it anyway.
If it ain't broke I'll fix it until it is.

El Scorcho

Thanks for having a look at guys, I really appreciate it! I'll order some parts.
  Phil, do you think I should use the 1N914's in the schematic, or could I go with LEDs?

El Scorcho

 And, yeah the way C2 is stuck in there doesn't look like a factory job.


The cap at D1 looks factory to me, it even has the paint on top.  It's solder connections do not look like they have been disturbed.

The ground pin of the bridge rectifier looks like a bad solder joint that has been arcing.  Suggest you resolder it and see if it does anything for the fizz.  Beyond that, if you can wait a bit I will try to draw out the bias circuit for this version, then we will have a better idea how to adjust it.

Jazz P Bass

To me, that amp appears factory.

Yes, right down to the bad solder joint on the bridge rectifier.:(