Marshall 8100 Guitar Amplifier

UPDATE: 12/05/2025

A user built this project and informed me of some mistakes- I have corrected these mistakes and subitted a new, corrected schematic and gerber files ! I apologize for any inconventiences! Please read the comments below!

I was asked if I could lay out a schematic/circuit board of a complex guitar amp by #Marshall, model 8100 , which is a 100 Watt, 2-Channel Amp (foot switchable) with built in Reverb Tank.

It is an especially confusing circuit, because it uses a special opamp (M5201) that has an internal switch- no substitutes exist that I can find.

Another oddity is that it does not switch between the Normal Channel and Boost Channel, but rather it ADDS the Boost Channel to the Normal Channel.

Also, there is a single 12AX7 vacuum tube in the Boost circuit, otherwise, it is a solid-state amplifier.

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This is my attempt to make a modified version of the 8100.

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I have substituted a Relay Circuit to engage the Boost Channel with the Normal Channel.

I replaced the single Vacuum Tube with two JFet Transistors to make this circuit easier to produce (no special High-Voltage Transformer will be required).

I have added RCA connectors for adding a Reverb Tank that is available on the internet (Amazon.com #2EB2C1B).

I have laid out a circuit board and laid out the Potentiometers, Switches and Jacks as they appear on the actual amplifier.

Circuit is not verified.