Things With Strings

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 Marsha

I've got a Vox Pathfinder 10 amplifier that I bought a couple of years ago, and I love it. It's a great little amplifier, but I don't care for the distortion channel, it just sounds harsh to my ears. There are quite simple modifications that can be done to this amplifier to remove the clipping LED's and increase the boost of the clean channel (check out Ben Craven's mods  for details). I'd been considering doing some of these, but whilst researching the subject, I discovered that the currently out of production (as at Nov '18)  Pathfinder 15/15R generally receives a lot more love than the Pathfinder 10. I found schematics for both the PF15 and the PF15R online, and saw that there were a lot of similarities between the PF10 and the PF15, particularly the earlier non-reverb PF15. The PF15R (with reverb) is quite a bit different after the first two opamp stages. I thought I'd model both the PF10 and PF15 pre-amp stages in LTspice  to see how they compar