i have a JCM900 and i love it. however, the clean channel has a very early breakup. I want to give it like, more headroom, and i don't know how to.i was wondering if it was easy to do it or not.

Not really. if you want louder clean, you're gonna need a louder amp. You could try different lower gain tubes, but I wouldn't mess with the circuitry itself.
but what in the amp makes it break up so early? if i can find out, i might be able to change it to get it to stay clean at higher levels.

EDIT: also, i'm looking to add more gain to my distortion channel. i use an OD to get the desired amount of distortion, but i don't really like having to tap dance to go from clean to distorted. i was thinking removing the OD from it's chassis and solder it right at the beginning of the distortion channel. would that work?
Last edited by jpetrucci5655 at May 26, 2006,
Well it is the High Gain JCM :-p. Research different tubes. I reallly wouldn't mess with the wiring and whatnot.. See what different kind of tubes would be best for your type of sounds. Maybe look into a different amp?

no, i love the amp, i use distortion mostly, but i also need clean cleans, but it's not a major issue. plus it would be fun to work on the amp myself and have it basialy customized.
I would say, use low gain tubes on the clean channel, and high gain tubes for the drive channel.

Besides the fact that I don't want to analyze the JCM900's circuit, and don't want to give you a wrong answer. The tubes are the simplest way to change the breakup in your amp.

Actually, in my Fender Blues Jr. I swapped out the 12ax7's for 12au7's (lower gain), and it hardly broke up at all, even when cranked up.
You could try replacing the 12ax7's with a 12ay7 set or 12at7 set for the lowest gain.
I'm not very active here on UG currently.
I'm a retired Supermod off to the greener pastures of the real world.
Quote by That_Pink_Queen
You could try replacing the 12ax7's with a 12ay7 set or 12at7 set for the lowest gain.

haha, exactly what i did!
I managed to salvage some 12au7's from an old tube organ.
now, i know i'm as newb and all, but won't this lower the distortion on the distortion channel?
the amp doesn't have a LOT of distortion on it, and i use an OD to get into metal territory.
or would it be possible to do the distortion thing i said in my 2nd post? where i would basicaly stick the OD in the beginning of the distortion channel, and that could compensate for the loss of gain. i might be wrong though.
I would seriously recommend against it. But if you REALLY wanted to, yes, you could.
^Yeah. Keep your amp as it is. This is what you can do: Every channel has their own tubes. Check wich tubes are for clean channel and what are for distortion channel. The change the tubes on the clean channel to 12ay7's or 12at7's
Quote by stratman_13
It's okay Gabel. You kick ass.

18watter video demo

My band

Recognised by the Official EG/GG&A Who To Listen To List 2009
on the JCM900 50W combo dual reverb, which are the clean preamp tubes? how can i find out?

would i still be able to do the distortion pedal mod? or is that extremely dangerous and hard?

i really wouldn't permanently modify your amp just so you don't have to press an extra stompbox. change the tubes, like the other guys said, and if you really need that extra gain have an extra gain stage professional fitted- this'll be an extra tube added to the circuitry, so the gain will be far more natural-sounding than with an OD pedal. Or you could get a looper that would allow you to turn on several pedals at the same time (ie the OD pedal and the channel switcher)
My gear;

Custom HSS Strat (eBay'ed parts)
Fender Acoustic
EH Big Muff
Home-made Wah
Home-made Booster
Laney LC15

Looking for a Jazz Bass body to refinish

My DeviantArt Page, MySpace Profile
i'm alrdy building a pedal that switches channels and changes between two loops at the same time, so i could just stick the OD in the loop that is assigned to the distortion channel and leave it on all the time, but i think it would be fun to modify my amp.

i find that using an OD pedal tightens everything up, and so i don't know if an extra gain stage is what i need since i like the tone i get when cranking the preamps gain and adjusting with the OD.