TIM CASWELL'S MARSHALL MOD
FRONT PANEL & BLOCK DIAGRAM




This diagram shows the architecture of the mod. When the Clean channel is selected (left footswitch green led on), the amp is essentially the same as the Normal channel of a 1959. Hitting the left footsw engages the Lead channel. If the #39 led (red)is off, the amp is essentially a MK II Master Volume. If the lower Xtra Gain toggle is towards the right, that gives the original‘Stage 1” mod that I did before #39. An amp with that mod was used on many of the 80's hits by the band Power Station, as well as many others. If the center footsw (#39) red led is lit, the extra tube stage is engaged. #39 didn't have the 2 extra gains, so for that sound, push both toggles to the left. The upper toggle engages the Xtra Gain for the extra tube stage. The amp that was used for the sound clips on the Les Paul forum had that permanently installed. The amps I did for George Lynch had both of tetra Gains permanently on, altho on his I installed 2 preamp controls, so the extreme amount of gain that created could be controlled. For the new version of the mod, I have included a Mid Boost, engaged by pulling the Treble control. Hopefully, some people may find this useful. The signal from the Tone section then goes to a Mosfet Buffer, and to the Effects Loop relay. The buffer isolates the external effects from the internal circuitry of the amp, and reduces the signal to Line Level, for compatibility with pro rack effects. Effects are returned to the other half of the new tube, to be amplified back up to the level needed to drive the power section of the amp. If the Effects Loop is off (yellow led off), the signal completely bypasses this circuitry.


© 2007 Tim Caswell. All rights reserved.