Marshal Origin 20 won’t distort when I turn up the gain

[Codyg]

Hello,

I’m trying to decide what to do with my Marshall origin 20 amp that won’t distort. My main question is could it be the tubes that are causing it not to distort? That’s the only thing I feel comfortable replacing, otherwise I will take it to repair which is an hour away, I think it’s still under warranty, have had it for 2.5 years. Thanks for the help,

Cody

[Jon Snell]

"It won'r distort" ... it's a Marshall and they do be default.
Can you be more specific please. Signal levels etc.
(I doubt the shop who sold it to you put a longer warranty than the standard 12 months).

[pdf64]

It’s a given that tubes will wear out and fail, one way or another, eventually. So there’s something of an obligation on tube amp users to have a spare tube that they know is good, of each type in their amp. Then anytime there’s a concern that something isn’t right, they are able to swap in the spare. If it doesn’t help, take it out, replace the original, and move on to the next tube socket.

[Mick Bailey]

Does the pull boost work? Also, is the volume reduced as well as the distortion?

With the master turned right down and the gain right up, do you get any real drive out of it?

[Codyg]

Jon - Thanks for your reply. This one does not distort. Levels are 2 volume and and gain 8

pdf64 - I guess I could try to switch out the tube one by one, but I’m not super comfortable with it so I thought I’d ask the experts before I try and buy tubes

Mick - the boost works with the foot switch that came with it, it makes the sound louder but does not distort, however pulling with the gain knob, which is suppose to do the same thing, does not increase the volume. I have never noticed this before, this makes me think it’s not the tubes.

thank you for your replies, I really appreciate them,

cody

[Helmholtz]

Please post schematic.

[Jazz P Bass]

From what I have read about these amps, you need a drive/ distortion pedal up in front.

[Jon Snell]

It is difficult to guess the fault without having it on the bench but we can make some assumptions.
If you mean the first stage won't go into clipping then that comes from V1, ECC83 a low noise high gain valve. This may be caused by a few issues.
Firstly the valve itself. If JJ or Chinesium valves, they have a short half life and do not last like Svetlana or other Eastern European large anode valves.
It could be just a low valve.
It could be C43 or C37 have dried out and no longer reacting in the circuit, causing low amplification.
It could be an anode load resistor has gone high value; R64 and R70.
It could be V2 after the return socket. It could be R4.2 with dirty contacts.
It could be the Send/Return sockets themselves.
If you input a signal on the return socket, is it strong sounding?
It could be low output from your instrument; low batttery if an active pickup etc.

The schematics are copyrighted and only available to Marshall Service Centres.

Lots of ifs I'm afraid but all I can do is guess.

[pontiacpete]

I had one of these come in last year and found the same thing, surprisingly very little gain compared to other Marshalls out there.

[Mick Bailey]

Mick - the boost works with the foot switch that came with it, it makes the sound louder but does not distort, however pulling with the gain knob, which is suppose to do the same thing, does not increase the volume. I have never noticed this before, this makes me think it’s not the tubes.

If I remember correctly, the footswitch overrides the pull boost and effectively disables it when connected.

[Helmholtz]

Here's a with test (sorry German) with sound clips for reference:
https://www.bonedo.de/artikel/einzel...ombo-test.html

[Codyg]

Jazz P Bass - that might be a work around I might consider but it distorted when I first got it and demos of it on YouTube distort. Thanks for your response

Jon - thanks for your reply. A lot of the stuff you mentioned is over my head. If I understand you correctly it could be the preamp tubes and it might be worth replacing them. It’s an hour drive to the nearest Marshall repair shop. Thanks again for your reply :-)

pontiacpete - thanks for your reply, did you end up fixing the distortion issue, mine is completely clean even on max gain. Thanks again

Mick - ah, good call. Thanks for the reply :-)

Helmholtz - thanks for the link, it bolstered my belief that my amp is faulty, mine is completely clean where the video distorts. Thanks again

[g1]

Have you tried putting a patch cord between the send & return jacks?

[Chuck H]

I like g1's suggestion. In fact I think any unsoldered contacts should be cleaned as a matter of course in this situation. Something that hasn't been discussed yet though, have we ruled out the guitar? I trust that in an effort to get the amp to distort you're turning the guitar volume full up?

Are you using any pedals between the guitar and amp that haven't been removed? I once had a customer call me all crabby about the amp I built him. He had no end of trouble with it at a gig and when he went to his backup rig everything was fine, so it MUST be the amp. Turns out his backup rig didn't include the tuner pedal he keeps in the chain full time with his main amp. The tuner pedal turned out to be the problem.

[Jazz P Bass]

"but it distorted when I first got it"

I feel that the OP should take it in to a shop, as he stated that he is willing to in the 1st post.