Marshall Lead 12 Preamp Simulation

Having already modelled the preamp stage of the Vox Pathfinder 10, 15 and 15R respectively, and noted the similarities circuit-wise between the PF10 and the PF15, I discovered another much-loved practice amp with a similar preamp stage - the Marshall Lead 12.

I should say, before going any further, that there are huge differences between the power amp stages. The PF10 uses a TDA2030A chip amp whereas the Lead 12 uses discrete components. The chip amp power stage on the PF10 shouldn't colour the tone much, but the discrete one in the Lead 12 most likely does contribute to the overall tone of the amplifier.

A simulation of the preamp stage with the Treble, Bass and Mid controls at 50% and the Gain control at 0%-100% gave this

Marshall Lead 12 Preamp Simulation

Marshall Lead 12 preamp simulation, Gain 0%-100%, TMB @ 50%

Vox Pathfinder 10 preamp simulation (overdrive engaged)

Vov Pathfinder 10 preamp simulation, Gain 0%-100%, T+B @ 50%

Comparing the two, the Marshall appears to distort more gracefully as the gain is increased, and the signal is not as compressed. Interestingly enough, the Marshall circuit is quite a lot simpler than the Vox, but like the PF15, it would be relatively easy to implement the Marshall preamp circuit on the PF10 board should anyone really want to try that. If I was to do it, I'd keep the PF10 tone stack as-is because it would be tricky to implement a TMB in place of the TB on the PF10 board. I did actually simulate a "hybrid" Lead 12 preamp with PF10 tone stack, and found that it really made very little difference anyway.

Interestingly, the PF10 does not implement the traditional Vox tone stack in the usual way, and the Lead 12 doesn't implement the traditional Marshall tone stack in the usual way either.

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