Taming a REALLY bright JCM800

[B2D]

Hey guys. My Legacy is in the repair shop and my cab is f-ed up right now, so I'm renting an old JCM800 2204 head and an old JCM800 cab in the inetrim. I'd be OK with this as a rental 'cept for one thing: This amp is INSANELY bright!!!!

I have the bass and the mids up all the way, the treble and the presence down to zero, and it's still ear-shatteringly bright, not mellow or smooth in the least... and FORGET about that traditional Marshall fatness. I used to own a really good JCM800 2x12 2204 combo so I know what these amps are supposed to sound like. I do use an attenuator to knock down the volume to levels that wont get the cops called on me but it doesnt affect the tone that much.

I cant get any weight or warmth to the tone. Its just bright bright BRIGHT. And its pissing me off.

Anyone got any suggestions on how to warm this thing up? It's running Groove Tube pres and EH power tubes, if that helps.

[Reckless Abandon]

Re: Taming a REALLY bright JCM800

JJ preamp tubes tamed my highs a bit. There are a few simple cap mods that you can do. Someone on here told me about them. But I had mine modded and I do not have to problem anymore. It is wierd it is that bright with an attenuator.

[Vasshu the humanoid typhoon]

Re: Taming a REALLY bright JCM800

Just play
It is prolly that cab that is loaded with stoopid gt-75's

[Gearjoneser]

Re: Taming a REALLY bright JCM800

Rent something else?

Since it's a rental, you could use this time to learn how to bias by ear. LOL
Just use a plastic handled miniscrewdriver, turn the chassis on it's side against the cab, and tweak the bias pot till the amp sounds it's best.....without getting the tube plates red of course. Have chops play the guitar while you're making small tweaks. When the amp sounds bold and healthy, it's biased.

[B2D]

Re: Taming a REALLY bright JCM800

JJ preamp tubes tamed my highs a bit. There are a few simple cap mods that you can do. Someone on here told me about them. But I had mine modded and I do not have to problem anymore.

This is a RENTAL.

[B2D]

Re: Taming a REALLY bright JCM800

Just play
It is prolly that cab that is loaded with stoopid gt-75's

Yeah i never liked those a whole lot either but I don't hate them THAT much. I mean I know those have pretty strident highs but this is just ridiculously trebly. Normally I don't let "less than satisfactory" tones get to me like this but this just keeps making me mad, mang. The worst part is that even with the treble and presence knobs on zero its still awfully bright.

Rent something else?

Since it's a rental, you could use this time to learn how to bias by ear. LOL
Just use a plastic handled miniscrewdriver, turn the chassis on it's side against the cab, and tweak the bias pot till the amp sounds it's best.....without getting the tube plates red of course. Have chops play the guitar while you're making small tweaks. When the amp sounds bold and healthy, it's biased.

The only other amps the shop had for rent was a Roland JC120 and a buncha cruddy SS Fenders from the 80's.

I might try that biasing by ear trick... I've never done that before so I'm gonna hafta be careful. Any definite no-no's I should know about?

[Reckless Abandon]

Re: Taming a REALLY bright JCM800

Just play
It is prolly that cab that is loaded with stoopid gt-75's

Putting those in helped me tame the brightness though. The V30's and the stock one which are close are too bright.

[Vasshu the humanoid typhoon]

Re: Taming a REALLY bright JCM800

Dunno never had the luck to get gt-75's to sound remotely good...weird speaker .

[Lake Placid Blues]

Re: Taming a REALLY bright JCM800

Yeah, the T75's can be insanely bright. My 4x12 had those when I first bought it, and it was like shards of glass. I tryed V30's because I got a good deal on a set, and even though the V30's are suppossed to be a bit bright, it was a massive improvement over the 75's. I don't know what to think of reports of the T75's as being warmer than V30's, because the set I had were way way way brighter than the Vintage 30's. The G12M70's also used during the early JCM800 era, are even brighter than the 75's. It may be a 70 loaded cab?

If you can, try it through another cab and see if it's really the speaker cab. I'm thinking that something may be wrong, perhaps a cold bias setting? Maybe the output tranny isn't right?

Even though it's a rental, I'd be tempted to clip the bright cap. Nobody would be the wiser.

[Farkus]

Re: Taming a REALLY bright JCM800

Dunno never had the luck to get gt-75's to sound remotely good...weird speaker .

I don't like them with any Marshall head I've played through them...but I love the 5150 through them.

[B2D]

Re: Taming a REALLY bright JCM800

Yeah, the T75's can be insanely bright. My 4x12 had those when I first bought it, and it was like shards of glass. I tryed V30's because I got a good deal on a set, and even though the V30's are suppossed to be a bit bright, it was a massive improvement over the 75's. I don't know what to think of reports of the T75's as being warmer than V30's, because the set I had were way way way brighter than the Vintage 30's. The G12M70's also used during the early JCM800 era, are even brighter than the 75's. It may be a 70 loaded cab?

If you can, try it through another cab and see if it's really the speaker cab. I'm thinking that something may be wrong, perhaps a cold bias setting? Maybe the output tranny isn't right?

Even though it's a rental, I'd be tempted to clip the bright cap. Nobody would be the wiser.

I'll open up the cab and find out whats in there... didn't know about G12M70s

I'll try another speaker cab as well.

Since it's a rental, I'm hesitant to start doing mods or tweaks... But what does the bright cap do and how do I find it? How do I clip it without disabling the whole amp?

[Lake Placid Blues]

Re: Taming a REALLY bright JCM800

Well being a rental you probably shouldn't mess with it. Nonetheless it's just a small cap that allows highs to by-pass the preamp volume control. Clipping one leg of it will not make the amp nonfunctional. It's Cap 5. On vertical input 2204's, it will may be right on the pot. On horizontal input 2204's it will probably be on the PCB, making it more difficult to disable. I don't know, something may be wrong with the amp for it to be that harsh.

[Jeff_H]

Re: Taming a REALLY bright JCM800

Not all 75's are stoopid. I happen to love mine, and I HATE bright amps. Plunk some JJ's in there for now. Since it's a rental, that's probably the best you can do.

[Mike M.]

Re: Taming a REALLY bright JCM800

Can you return the 800 for another amp that's not so trebley? If not, just plug your guitar into an EQ pedal then into the amps input. That's what I'm doing with my DSL 50. The treble is rather "over the top" to put it mildly. I took the far right sliders on the EQ down considerabley and took it from there. Such a simple thing and it made such a HUGE differance. No more "ice-pick treble."

[kmcguitars]

Re: Taming a REALLY bright JCM800

I'll open up the cab and find out whats in there... didn't know about G12M70s

I'll try another speaker cab as well.

Since it's a rental, I'm hesitant to start doing mods or tweaks... But what does the bright cap do and how do I find it? How do I clip it without disabling the whole amp?

The G12M70s are aweful speakers IMO. They have a upper Mid spike that you can't dial out without turning your tone to mud. I had a pair of them in a 77' Twin. (Talk about bright !!) Like a Idiot. I sold the amp,But kept the speakers.