Hey herby, I suspect the trim pot is a gain adjustment
, but others will know better than me. If you don't want outrageous gain and want to keep reasonable clean sound capability, then I don't think 3TM is the way to go for you. E.g. MJMP uses a 3TM for distorted sounds (coz he plays metal
) but uses a MP-2 for cleans.
Re doing it yourself, we can help talk you through it, it isn't (mostly) too hard to do. You do need a decent temperature controlled soldering iron, though they are not that expensive (eg a Duratech TS1513 (which I bought) or similar) and a few other bibs and bobs (like a solder sucker and/or solder wick). That said, any decent tech should have no problems doing the mods for you, buy the bits from MJMP (or source yourself) and get them to follow the instructions.
You don't need to understand schematics, all you need is the PCB layout to locate/find the various components you need to change out.
This is what I would do (advice LoL):
If your unit is a V1 (ie inst/line switch on top), do the rear jack mod first (http://www.marshalljmpmodshop.net/miscellaneous_parts_and_replacement_tubes.htm) this will get you into it, replace the front and rear input jacks and turn the rear jack into inst level (and isn't hard to do).
Do the MDRT and a new tube board, I'd go with the SS Mod tube board (http://www.marshalljmpmodshop.net/ada%20mp1%20ss%20mod.htm), a bit more gain, but otherwise upgraded stock tubeboard, modernised. Now IIRC the MDRT install requires a change on the tubeboard, so get it from MJMP MDRT ready (and a MDRT) and do them at the same time (this should be rather easy to do and you wont have to change the tubeboard component(s)). The only place you can buy a new MDRT is from MJMP, he gets a batch of them made from time to time to keep us all happy
. So it makes sense (well to me) to just get him to send everything you need (a nice little box will turn up with all the bits and include ADA Depot stickers
).
And last, do the noise mod, this is changing out the old caps.
Oh and maybe EPROM ? The last EPROM is 2.01, when you turn the unit on it will display the version.
Then either get a tech to do it (in the order above, or all at once), or do it yourself with some help and encouragement from us here
Harmonics you can chase (to some extent) with tube choice eg try a pair of New Sensor Mullard Long plates (http://www.dougstubes.com/preamp-tubes/12ax7-ecc83-7025/mullard-12ax7.html), they just sing mmmm