My Marshall JMP's sound changed from just sitting too long??

[nb_fan]

So I have a Marshall JMP 2203 from '79. The last time I played it was a couple months ago, and it was sounding absolutely great.

I started it up again today and it just sounded overly bright no matter what I did to the EQ

What could have happened?? It's been absolutely untouched since then. Guitars have been the same, room the same, power source the same.

it was left in a large room that probably the coldest is ever gets is about 10 C/ 50 F and normally sits a bit higher than that.

The last time I played it was shortly after it went through a full reservice, new tubes, some new caps, etc.

Can an amp lose it's tone by just sitting there for a couple months?

I've heard of gear needing to be 'reawakened', but that's after years of not playing it..

Dust collected inside the chassis maybe?

[phsyconoodler]

Usually the last thing that was done to the amp is the cause of future problems.Recheck your work and make sure one of your tubes isn't redplating.

[nb_fan]

Last thing in terms of just an overall checkup, I had a couple of caps replaced.. and I had some tubes replaced and rebiased. But that was about a month before the last time I played it (mid december). The last time I played it (beginning of February), I'd say it was the best the amp had ever sounded. I didn't do anything to it after that. Just let it sit, unplugged, untouched for about a month and a bit.

It now sounds brittle and there's so much high end coming through. I have the treble turned down to 1-2, the mids backed to 3-4, and the bass 5-6, presence completely off. no matter where on the volume/gain settings, it sounds brittle. It's almost icepick bright when the gain down, and it starts to thicken with the gain up, but still sounds relatively brittle. I tried both high and low inputs, and anywhere from the MV being 1 all the way to the MV close to 7... all the same brittle high end. I looked at the tubes after about 30 minutes of playing and there's nothing out of the ordinary.. faint orange glow is all I see.

you think something like having caps failing could be the problem?

[PRNDL]

More likely a preamp tube has gone south.

[nb_fan]

mmm.. the preamp tubes are brand new too.. less than 10 hours of play I'm guessing.
EHX 12ax7s... you think they were just bad tubes being used?

[DavidH]

Have you been playing a darker sounding amp in the mean time? Your perception will change,it's possible it sounds exactly as it did when you put it away.Happens to me all the time until i get used to an amp again.

[nb_fan]

Have you been playing a darker sounding amp in the mean time? Your perception will change,it's possible it sounds exactly as it did when you put it away.Happens to me all the time until i get used to an amp again.

on the contrary! I've been playing my deluxe reverb this whole time... i was gonna go back to the marshall cause i missed the deep low end sound.
Unless i'm losing my mind, there's definitely something funny goin on with the amp

[DavidH]

I see.Not that then,just thought i'd throw that in there.

I'd start with the pre tubes then,try swapping them around if you don't have any spares.

[jezzzz2003]

Being A Long Time Jmp Player Myself, My Guess Is Simply The Bright Channel Volume And Where It Was Set.

[JimmyR]

Not a huge fan of EH tubes. That would be the first thing I'd check.

[nb_fan]

Definitely gonna do a check of all the tubes later this week.

Thanks for all the suggestions, everyone

[phsyconoodler]

the preamp tubes are likely NOT the problem.I would suggest trying another pair of power tubes just to see if there is an improvement.You might have one bad power tube and that would definitely make it thin sounding.

[nb_fan]

First off, Happy New Year everyone.

Secondly, I'm sort of resurrecting this thread because I'm still having kind of the same problem.
It's been a long time, but I've swapped out both the preamp tubes and the power tubes with older working ones that should sound at least decent.

Here's the odd thing....It sounds KILLER with my SG.. classic '57 humbuckers. It's still very bright, but I'm starting to think that maybe the tech switched a bright cap value too high. Still running it with treble and mids down at 2-3, bass 6-7 and presence ~3. I've got master set ~7 and pre-gain ~3.

HOWEVER, when I switch over to the strat (all US stock strat pickups), it sounds like the amp is gonna die. It's horrible. It's brittle, one dimensional, and just a really gross sound overall. I've tried all forms of EQing and the best sound is with the master at 10 and preamp at 2. Slight breakup, fatter cleans....but it still sounds like a toy compared to what it used to sound like (just a year ago). I'm so frustrated with this amp because I've tried everything short of just bringing back to a tech, which I'm trying not to do because I just spent over $200 getting the amp fixed up and I've barely had 30 hours on the thing since a year ago. (btw, the strat sounds great through my DRRI and EVJ with and without pedals in front)

Anyone have any ideas? Will clipping the bright cap solve the brittleness or is there something deeper than needs to be done?

Thanks

[phsyconoodler]

that sounds like the typical bright cap issue.Clip it off the volume control,or master on your amp.
Low output strats can sound pretty thin through a marshall without some tone tweaking to your guitar.Turn the tone controls down on the guitar.Play with less gain or plug into the low input.Those are usually the cat's meow with a strat.

[Ronsonic]

Are you playing at a lower gain setting than before?

The lower the volume control, the more effect the bright cap has.

[davemccarthy707]

mmm.. the preamp tubes are brand new too.. less than 10 hours of play I'm guessing.
EHX 12ax7s... you think they were just bad tubes being used?
EH tubes there is your problem. I NEVER use their pre's. They always have given me weird problems in the past. Goin south for no reason. etc.

[nb_fan]

I swapped out the EHx's for JJ's. I've tried EHx EL34s and Svetlana EL34s... the Svetlana's are slightly smoother and not as brittle, but doesn't solve the problem at all.


As for the gain, I've been trying it at all different volumes. Loud enough to shake windows in my house... all the same.

The bright cap is on the gain knob. I think I might clip it out soon. When the gain is anywhere under 6, it's icepick and brittle. Bass has to go up to 6 or 7 and treble, mid and presence are 0-3 depending on the guitar. the gain knob from 7 to 10 goes from dark and too really dark and then the bass starts farting out. I then have to re-EQ everything so that they're all almost at 5. MV anywhere from 2 to 7 - same EQ problem.

Aside from the EQ problem, it also sounds brittle with the strat at any setting on the amp. The more gain, the more brittle it sounds. With the SG, it doesn't sound brittle.

I'm just gonna clip the bright cap when I get the chance and see if that helps with the brittleness.

By the way, should I be removing the bright cap all together or replacing it with a lower value?

[JamesHealey]

JJ's are horrid in Marshalls in the pre amp, they have a woofy bass and all sorts of issues, the best sounding are nos mazda grey plate or mullard but in a realisitc world try the tungsol reissues but not in v2 they have problems with the cathode follower circuit and tend to blow, try a JJ in here.

[Mr. SD-1]

If your 2203 has been sitting unused for some time, you might want to try cleaning the switch contacts on the lo gain input jack. Sometimes plugging/unplugging in the lo gain jack a few times works too. The lo gain input is a signal switching jack; corrosion formed on the contacts can mess with the tone and gain of the amp.

[TheArchitect]

So I have a Marshall JMP 2203 from '79. The last time I played it was a couple months ago, and it was sounding absolutely great.

I started it up again today and it just sounded overly bright no matter what I did to the EQ

What could have happened?? It's been absolutely untouched since then. Guitars have been the same, room the same, power source the same.

it was left in a large room that probably the coldest is ever gets is about 10 C/ 50 F and normally sits a bit higher than that.

The last time I played it was shortly after it went through a full reservice, new tubes, some new caps, etc.

Can an amp lose it's tone by just sitting there for a couple months?

I've heard of gear needing to be 'reawakened', but that's after years of not playing it..

Dust collected inside the chassis maybe?

After extended periods your memory of the sound and the reality become different things. I would submit there may be nothing wrong with it.

[JDJ]

Sometimes the power coming out of the wall in my house is noisy and makes all of my amps sound brittle. And then it goes away and all is good again.

[EVHindenberg]

Could the bias have drifted low since the last time you played it? It does happen.It may have drifted into crossover distortion.That's what it sounds like based on your description of the sound.

[Ronsonic]

Do give the bias a check to be sure.

Another note, there are two "bright caps" the obvious one on the volume pot and another bypassing a 470K resistor that feeds the grid of V2. I like the one on the volume control, and prefer to remove this other one first. You can find it by looking at pins 2 & 7 of V2. One of those is going to be hardwired at the socket to another pin, so look at the other and follow it back to the board and clip the 470pF cap that is connected to it.