Marshall JMP advice

danlpt

A friend of mine is considering selling me his 1980 2204 JMP but I have a couple of questions about these....

1) I've noticed it's perfect with Humbuckers but a little too bright with single coils (my main pickup live), he mentioned there's a bright cap mod that leaves the amp pretty unmolested but will get rid of some of the brightness for me? Is this an easy mod to do? 

2)Obviously taking account of how well they have been looked after, how reliable are these as a main gigging workhorse now they're getting on a bit? I've never ran a vintage amp as my main before. He's owned it 15 years and its only really been a studio tool for bands he records and has sent it to Marshall a couple of times, but before that i'm not sure.
Are there any common issues I should be aware of?


Any input greatly appreciated 

shaunm

@Moltisanti has a good deal of gigging experience with a 2204. 

I got one one a couple of months ago and it's great fun, a super sounding rock amp.

GoldenEraGuitars

As the ex owner of several 77-79 2203s and 2204s I can honestly say they are fantastic workhorses. Any issues are relatively simply for an amp tech to fix. Imo and experience the JCM800 line was the last of the Marshalls that was pretty simple and straight forward to own and service. 

Youre in for a real treat, those amps are amazing.

ICBM

If it's a 1980 the bright cap is very easy because the cap is not mounted on the PCB. There are actually two - one on the gain pot, and one on the resistor that feeds it. You can see both here:

http://i46.photobucket.com/albums/f112/gldtp99/Marshall 2204 1981/IMG_5031_zps75b97932.jpg

(Sorry for the Photobucket link, it's the best pic I could find.)

The one on the pot has less effect as you turn the gain up, so if you find it too bright at low settings but OK full up, cut this one. The one on the resistor has the same effect at all settings so if the amp is simply too bright overall, cut this one.

In either case only cut one leg of the cap and just leave a small gap in the wire, in case you want to put it back - then you just solder the cut ends back together.

Apart from the general need to replace electrolytic caps - which has probably been done if it's been back to Marshall in the last ten years - there is nothing which goes wrong with these. By 1980 they were using proper rotary switches for the voltage and impedance selectors so those aren't an issue. If the caps *haven't* been done, it's a good idea to at least change the bias caps, these fail more often than the main ones.

danlpt

Thanks everyone. Yes it had the caps changed 3 years ago so I'm assuming that's given it some new life.

and thanks ICBM for the advice on the mod. 

Reverend

I have the bright cap mod on my main 2203. Sounds great and there is nothing I'd consider swapping it for. 

riffpowers

One of the best rythmn guitar amps ever, Solid, and reliable when looked after. I love em!! Never found em too bright, although a lot of people do. Put a boost in front and it'll sound even better.

Moltisanti

i've run mine with the presence on zero and the treble and mids very low too - don;t be scared to EQ the brightness out of it. I like the chime the bright cap gives at low volume so left it stock. I did try it with it clipped but it sounded a little lifeless at quieter volumes.

They are so simple that there's very little to go wrong, all easy fixes for a tech

danlpt

Sounds like I'm buying this amp then! Thanks for the advice everyone. 
I agree JMPs are the perfect basic rhythm amp.

danlpt

So I picked the JMP up this morning and got it for a decent 'mates rates' price. Loving so far. Doesnt seem so bright through my cab. Can't wait to push it a little further on its debut gig.

Reverend

Pretty damn good for lead as well. 

TTBZ

Enjoy. My dream amp, the one I use in our rehearsal room is so good and he won't sell it to me!

danlpt

TTBZ said:

Enjoy. My dream amp, the one I use in our rehearsal room is so good and he won't sell it to me!

It took some convincing to get this one!

Collings

I gigged one of these for a few years and really regret selling it. Mine was stock with no mods and tended to bright unless it go up to decent gig volume.

danlpt

First gig with the JMP last weekend, performed flawlessly and sounded great through my PPC212 with greenbacks.

Set just past the point of breakup for a nice very responsive crunch and hit with my OCD to kick things up a notch or two.

Perfect 

Reverend

https://scontent.fstn1-1.fna.fbcdn.net/v/t31.0-8/fr/cp0/e15/q65/17493132_10154178271216883_975795015294912119_o.jpg?efg=eyJpIjoidCJ9&oh=a4085a65fc666dd4cbfdccf3d28020c5&oe=5960BF46
Recording yesterday.

danlpt

I bet it sounds great through a proper marshall cab too. What's it loaded with?

danlpt

I'm using a closed back PPC212 with a v30 and a greenback but im hoping to go to a 1960bx at some point.

ICBM

danlpt said:

I'm using a closed back PPC212 with a v30 and a greenback but im hoping to go to a 1960bx at some point.

If you're cranking it to anything like full volume I would be careful with that Greenback. A 2204 will comfortably put out well over 50W even clean, and a lot more than that when the power stage overdrives.

Ironically simply disconnecting the Greenback (and setting the amp for the impedance of the V30 obviously) will increase the power rating, although maybe still not quite enough. Much better to replace the Greenback with something with more similar power rating to the V30. If you want to keep the Greenback sound, a G12M-65 Creamback is the closest.

danlpt

ICBM said:

danlpt said:

I'm using a closed back PPC212 with a v30 and a greenback but im hoping to go to a 1960bx at some point.

If you're cranking it to anything like full volume I would be careful with that Greenback. A 2204 will comfortably put out well over 50W even clean, and a lot more than that when the power stage overdrives.

Ironically simply disconnecting the Greenback (and setting the amp for the impedance of the V30 obviously) will increase the power rating, although maybe still not quite enough. Much better to replace the Greenback with something with more similar power rating to the V30. If you want to keep the Greenback sound, a G12M-65 Creamback is the closest.

Thanks, i'll look into the G12-M i'm not running it close to full on the master, i've learned by now this amp is pretty damn loud as expected! I'm usually around half way on the master with the preamp around 1 oclock

ICBM

danlpt said:

Thanks, i'll look into the G12-M i'm not running it close to full on the master, i've learned by now this amp is pretty damn loud as expected! I'm usually around half way with the preamp around 1 oclock

That's getting risky. It doesn't need to be anywhere near full up on the master to be at full power - the power amp usually goes into overdrive at about 6, if the preamp is already overdriven. You'll probably hear the sound change as you reach that point - after that it won't get a lot louder, just smoother and more compressed.

In theory a pair of 25W Celestions should just about be able to handle a cranked 50W amp, but these are a bit more than 50W amps . Marshall fitted the combo version with a pair of Blackback 25s originally, and blown speakers are common.