marshall JTM 30 mods

[bmd]

I would like to add; 12v fan, pre amp diode clipping switch, FX loop mix w/dry & on off footswitch,
reverb on/off footswitch, Bias trim pot, ( choke ? ) I fixed bias on '99 TSL 100 with help from this forum.
This amp could also use separate tone stack (treble boost ?), for boost channel.
I can DRAIN CAPS, do the mods but I don't have the knowledge to select components & design mods.
I have seen bias mods but there seems to be different ideas.
Any help would be really cool.

[olddawg]

Seriously...no disrespect intended. You would be better served buying a new amp with the features you want rather than trying to extensively re-engineer that one. You will be opening a very large bucket of worms. Just my opinion of course, but adding channels, loops, etc is not a small endeavor and there are lots of unforeseen consequences. When you consider the time and expense it doesn't make sense.

[Chuck H]

+1
Other than the extra diode clipping circuit the JTM60 does have the fetures you want. Adding diode clipping to a JTM60 would be much easier than tearing down the JTM30.

Dificulty level:
Fan easy
diode clipping moderate
fx loop on/off + mix hard (remember, it's a PCB)
reverb on/off moderate
bias trim pot moderate
choke moderate

Doing ALL these mods to the same PCB amp without peripheral problems HARD

[olddawg]

Instead of diode clipping why don't you just try a Pro Co Rat pedal on the input? A lot simpler and is pretty much what everyone does. I mean you can use any dirt box you want, but Marshalls love Rats. I think the older ones sound the best but it's all subjective. If it were my setup I would use a Bad Monkey OD and a Rat into that amp to balls it up. Makes it like a 3 channel amp.

[Chuck H]

Another +1

But I'd go a step further and invest in a reissue white face rat. That was my rig for all my time prior to amp mods and building. A Plexi with a master volume mod into a quad of g12h30's. My pedal board was a modded wah, my mid 80's RAT, a chorus, an old mxr phase shift and a delay. Just the baddest rig ever. The tone it had lives in my head as a built in gauge for whether or not my designs sound good.

I've heard clips of the reissue WF RAT and it's so right.

[olddawg]

Yeah my club rig is a Marshall 18 watt variant into a 4x10 (or 2x12) cab with a Cry Baby, a 70s MXR Phase 100, a Bad Monkey, an early 80s Rat, an old Ibanez CS 9 Chorus, and a new DD7 delay.

[Chuck H]

[Steve A.]

I have a JTM30-112 and it does have clipping diodes on the OD channel- I've been thinking of removing them to make the OD channel less muddy (to my ears, at least).

While I was gung-ho about "all tube audio signal paths" 10 years ago I really like the boutique pedals that have come out since then. Even some of the not so boutique-y ones. So I tell people all of the time to forget about modding their tube amps and just find an FX pedal or multiprocessor that sounds good plugged into the clean channel. I think that you can get a better sound from a nice OD pedal than most of the OD channels on the mass-produced tube amps you might find at GC- the big amp companies don't seem to understand the finer qualities of distortion as well as the builders of boutique OD pedals. Like the Barber Small Fry, the Hermida Zendrive and the Ethos. The Fulltone ODS has some great lower gain OD sounds and cleans up really nicely as you back off on the guitar volume control. For a multiprocessor I think that the Vox ToneLabST gets some great OD sounds.

Just my 27 1/2 cents...

Steve Ahola

[Chuck H]

So I tell people all of the time to forget about modding their tube amps and just find an FX pedal or multiprocessor that sounds good plugged into the clean channel. I think that you can get a better sound from a nice OD pedal than most of the OD channels on the mass-produced tube amps you might find at GC

+1
I think you can do better with an all tube circuit. But not much. It's hardly worth the trouble. And a pedal will still usually offer greater versitility. I build "all tube" because I can and it's as much a hobby as a side line for me.

If you like the "boutique" pedals you should defintely get into a reissue RAT. No kidding. It's the voice of rock from '84 to '90. Jimmi Page, Joe walsh and even Zakk Wylde. Side by side with an original you can't tell the difference. And you can't go wrong. I sooo wish I still had mine (stolen). I want to get one myself but other projects clutter the budget right now. I hope I don't miss my window before they get too expensive.

I even thought about cloning just the guts complete with correct chip (which can still be found but is no longer in production) and selling them on Ebay for guys to stuff into their new Rat pedals. Just not convinced there's enough market to make it worth the time.