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I spent way too much time trying to figure out why I couldn't get much out of the power amp when plugging into the FX return jack. The output would be very weak with a weird distortion, yet everything was fine when using the normal input.
My excuse will be trying to follow signal through modern Marshall schems.
Anyway, it turns out the standard input jack with nothing plugged in will mute the FX return jack. I guess they don't expect anyone to try to use the power amp on its own.
In the schematic you can see at the tube grid the "FXLPOUT" line which is where the FX return eventually ends up. On the other side of R15 is a 100N cap that connects to the ground switch of the input jack.
So you need a dummy plug in the input jack to use the FX return on its own.
Not sure if I feel more frustrated or embarrassed.
.
Thought I'd mention it as it kind of messes up the standard troubleshooting procedure of isolating preamp/poweramp via FX loop.
v265-62-02.pdf
My excuse will be trying to follow signal through modern Marshall schems.
Anyway, it turns out the standard input jack with nothing plugged in will mute the FX return jack. I guess they don't expect anyone to try to use the power amp on its own.
In the schematic you can see at the tube grid the "FXLPOUT" line which is where the FX return eventually ends up. On the other side of R15 is a 100N cap that connects to the ground switch of the input jack.
So you need a dummy plug in the input jack to use the FX return on its own.
Not sure if I feel more frustrated or embarrassed.
.Thought I'd mention it as it kind of messes up the standard troubleshooting procedure of isolating preamp/poweramp via FX loop.
v265-62-02.pdf