JMP1 gain stage

Hi guys, I already introduced myself over at off topic

Sorry if this has already been mentioned? (Though I couldn't find it anywhere) But does anyone know if Trace mods the diode clipper ? I.E. bypasses it for the two 12AX7 tubes to completely take over? I know there wouldn't be as much gain for the likes of metal players with just two, but...

That is a very good question, I would also like to know as I own one (platinum mod)

I just found this, it is a replay on whether or not the tubes play a role in the tone section..diode clipping...

Q) "after reading some other posts regarding this unit. and the fact that it supposably uses diodes to get its distorted tones. i contacted marshall and asked them about wether the jmp-1 is a tube preamp or a solid state preamp that uses tubes to just warm up the sound a bit. here is the respones i got from them.

Marshalls Response:

A) The JMP-1 preamp is built around 2 ECC83 tubes (4 tube gain stages) and the sound is largely based on the tubes themselves. There are a lot of programmable parameters built into the JMP-1 which require control circuits comprised of IC's as well as some IC's used as buffers or as a part of those controlled stages. There is one solid-state clipping circuit comprised of BR3 which is a diode bridge, but that only kicks in if the signal level is over 1.2 Volts and it's found just before the first tube which is quite early in the signal path. You can have it removed by a qualified tech but you'll see that it contributes to a somewhat overall "roundness" of the tone for lack of a better term. It levels off some harmonic spikes and generally doesn't affect the fundamentals unless the input is extremely hot or has been insanely boosted by another pedal or preamp. As far as the so-called 'experts' are concerned, yes, if you bypass the tubes and max out all the gain you will still get some clipping. However, the overall QUALITY of the tone in the JMP-1 does come from the tubes alone. I hope this answers your question.

I found it here:
http://www.harmonycentral.com/t5/Rack-S ... d-p/203983

One (1) 12AX7 is used for the gain channel and the other 12AX7 is used for the clean channel. The clipping circuit is necessary to achieve the level of gain the JMP-1 contains. You can remove the clipping circuit from the preamp tough in doing so there will be very little gain comparatively. IE: a single 12AX7 cannot generate what we know as high gain as there are not enough gain stages to do so.


Many thanks & all the best!
Trace

Thanks Trace!