Solid State Guitar Amp Forum | DIY Guitar Amplifiers

Hi people,
I'm new here and I'm realy glad I found such a nice comunity. I do not have experience with guitar amps so maybe you could help me with my dilemma?
I would like my Marshall Master Lead Combo 5010 to have "Power-amp in" jack because I sometimes play my guitar through modeler and would like to bypass Marshall's Preamp. It would be even better if "Power-amp in" would have its own volume pot. Is it possible?

You will probably need to locate and cut a trace on the PCB.

Edit: Bonus feature... Your amp will now have a low level hum.

Ok, thanks for your response. Could you be more specific about low level hum. Why is it happening what can I do to avoid it? Can you elaborate?
P.S.
Thanks for new schematic.

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I think it should be read: "it will have a lower level hum" and that because the preamp is bypassed.

And I'd add just 1 jack, the one before the master volume control.
Worst case, you set it to 10 and it's practically out of the circuit.

Often times when two pieces of equipment are connected together with single ended cables, a ground loop is created. The amount of hum picked up is highly variable and depends on many factors. Since the 5010 was not intended to receive an external signal other than at the guitar input, there may be significant hum between signal ground and the mains power input safety ground.

One thing to avoid is using the chassis of the 5010 as a ground for the new jack. Connect the jack's ground to a ground at the Master Volume pot on the PCB.

OK folks, thank you very much. I made it. Everything is OK now. I did't have an switched jack so I used 1 spdt switch and mono jack. I have no hum at all. But the schematic I posted (I found it on the net) is not 100% correct for my amp.