I bought this unit second hand because it was cheap and I believed the hype. I've used it for recording and live through a el84 power amp, both through a 4x12 and two 1x12's. I have read harmony central reviews millions of times but have never felt so strongly as to write one. This unit is a piece of garbage, and before you make assumptions about the credibility of this review I am a guitar teacher/session player and have used every amp under the sun and to good effect. Pound for pound this is the worst piece of kit I've ever used. Firstly,the term valve preamp is very misleading as the JMP sounds transisterized. I suspect that the valves are part of the EQ circuit as with some valvestate gear. How, therefore, do Marshall justify the cost of this festering turd of a preamp.
To be more specific then, the clean channel is thin and lifeless and although I don't expect a Marshall to sound like a Fender, I normally quite like Marshall cleans as they're good for rythym (not being overly intrusive).
The 1st overdrive channel is a waste of time. The second overdrive channel can produce some reasonable harmonics and overtones but still within the confines of a preamp lacking in body and tone.
Furthurmore, what is going on with the FX loop? It does next to nothing from increments 0-6, after which point you're swimming in effects.
Believe me, I don't wish to be one of these people that gives everything a 1 or 10 out of 10, but considering the cost of this unit it deserves a 1. Had the asking price been ¿¿150 brand new I would give it a generous 3....maybe.
I hope this review is of use to someone, as I am writing it as a warning to potential buyers. If you however like the sound of this preamp, then I know a really good ear, nose and throat specialist who can help sort out your ears.
I have to play everything in my profession and this unit does nothing well. In my 18 years of playing I have used Boogies, Laneys, Torres, Fenders and countless Marshalls of which I still own a JCM800 4212 (superb, by the way-how a Marshall should sound), and nothing has offended my ear sufficiently for me to feel the need to warn others. I know why so many people use these things. On paper it's the perfect preamp;-small, light, flexible, MIDI switchable etc etc. I wanted to like it for the same reasons and I think that Marshall have played on this.
I've already sold the JMP1 now, but had someone stolen it I'd have had to hunt them down and shake their hand.
It's a shame you can't add to these reviews later, becaues I feel I've forgotten to rant about something, there is so much wrong with this unit!