Modifying JCM800 2204 for treble boost pedal?

Pythonman

Member
Messages
409
I purchased a new BSM Hornby Skewes treble boost and it's wonderful through my AC15C1 but I get a pretty horrendous amount of hiss and racket through the hi input of my stock JCM800 2204. Will removing the bright cap at C5 be enough of a mod to get this amp to work better with a treble boost pedal or will I need to remove/mod the treble peaking circuit as well? I have to say that I have tried the bright cap removal before and was less than impressed with the sounds of the amp because it removed a good chunk of gain and smack and the amp just sounded sorta lame. I've read removing the peaking circuit and possibly replacing it with a 68k resistor actually adds a bit of gain back into the circuit? Any thoughts would be appreciated!!
 

QRSS

brutalist
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9,373
nope, that amp dont need a treble boost. it's built in. save the pedal for dark amps.
 

michael patrick

Loud and proud
Silver Supporting Member
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10,862
I never would have thought of modding an amp to suit a pedal. That just doesn't compute for me.

Some pedals work well with some amps but not others. Just the way it is.
 

V-man

Member
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2,794
:agree

Try the low sensitivity jack and dialing the pedal. If that fails, wrong pedal. Modify it off your board. I have a few 2203s and a 1959RR with a Beano Boost Treble Booster. It sounds fine through them and I wouldn't think to mod them to make it work.
 

Pythonman

Member
Messages
409
nope, that amp dont need a treble boost. it's built in. save the pedal for dark amps.
Truest thing I've probably read yet. Truth is, with my Les Paul R7 R8 and R9s this amp is perfect in stock form into either or both of my Marshall 4x12s. I'll have to just leave it as is and try a 4 holer Marshall down the road. The low input channel seems useable with my Hofner Beatle bass on occasion but even with the BSM pedal there's not enough grind with my Strat through that input. OK, the amp stays stock and till then I wail the Strat through the AC15 into my 1960BHW cab with the boost pedal. Thanks guys, I really didn't want to have to go down the modding road and to do it just for a pedal makes no sense, at all.
 

wildschwein

Member
Messages
4,022
Treble boosts (which are kind of half way to being a fuzz pedal) were made for amps in the 60s which were lower gain and generally darker than the 800. Lots of Brit guitarists used them to get more sizzle and gain out of their amps - as noted above the JCM 800s don't really need it as they're already gained out.
 

michael.e

Silver Supporting Member
Messages
20,526
Too many misconceptions here. Low input and guitar volume are your friends.
 

Belmont

Member
Messages
3,465
it's how you set the amp, not the amp itself. Tony Iommi uses a treble booster (really a full range or midbooster, not literally a "treble" booster at all) into a higher gain amp than a JCM800.
you can run them into whatever amp you want, maybe in the 60's the idea was to brighten a dark amp but the (typical) modern use of TB's is too add midrange, tighten the low end and add that hint of crispness or crunch to the attack of notes/chords.
that's my take.
 

michael.e

Silver Supporting Member
Messages
20,526
You could just keep the gain low in the high input anyway. These are HUGELY versatile amps. I have no need to mod mine in any way.

Live, I usually have mine set at 4 on both volumes, high input for balls out rock.

For other types of music, I use the low input a lot. Gorgeous cleans from this amp.
 

Pythonman

Member
Messages
409
it's how you set the amp, not the amp itself. Tony Iommi uses a treble booster (really a full range or midbooster, not literally a "treble" booster at all) into a higher gain amp than a JCM800.
you can run them into whatever amp you want, maybe in the 60's the idea was to brighten a dark amp but the (typical) modern use of TB's is too add midrange, tighten the low end and add that hint of crispness or crunch to the attack of notes/chords.
that's my take.
Well, what I noted with my AC15c1 (especially through my BHW cab) is that the louder the amp was set the better the overall effect of the treble boost and the less noise and hiss. It's actually quite controllable into the bright top boost channel of that amp as long as I set the amp and preamp vol. above 5 or 6 minimum. I suppose I could get that through the 2204 but by then my ears would be toast and the cops would be bustin' out my front door. With the AC15C1 I try to set the amp darkly on it's own with just a bit of grind. Nice dark and fat sounding with the bass up, the treble down and the treble cut up quite a bit. Then when the HS-S Master is engaged my Strat instantly cops the My Woman From Tokyo's growling opening riff and it also aquires plenty of added upper midrange sparkle without ever becoming too bright or harsh. It is a midrangey boost with a solid and tight low end and a singing and velvety high end.
 

Pythonman

Member
Messages
409
You could just keep the gain low in the high input anyway. These are HUGELY versatile amps. I have no need to mod mine in any way.

Live, I usually have mine set at 4 on both volumes, high input for balls out rock.

For other types of music, I use the low input a lot. Gorgeous cleans from this amp.
I will try this next. As you know the treble really kicks in with the preamp gain reduced so I'll try boosting the bass and dropping the mids, presence and treble way back before kicking in the booster pedal and see if I can't find a way to use that. It is a versatile amp. After years of burning up output tubes through a slew of different plexi type Marshalls and using those rediculous attenuators I've given up on them and gone strictly with MV Marshalls and they've just plain worked out better for me overall. Heck, a set of RFT EL34s I put into this particular 2204 back in 2010 still rock like new!
 

mesa/kramer

Member
Messages
3,053
Why would you need a treble boost with one of the brightest amps made?

Get a Tube Screamer and Rockit!

Even a Graphic EQ Pedal would be a much better option
 

Pythonman

Member
Messages
409
Why would you need a treble boost with one of the brightest amps made?

Get a Tube Screamer and Rockit!

Even a Graphic EQ Pedal would be a much better option
I wanted the treble boost for my Stratocaster (and Brian May Red Special) to get specific tones that a tube screamer or other overdrive boxes are incapable of. It just so happens I have a JCM800 and was trying to see if there was a way I could use the boost pedal with my Strat through it to get the same tones.

Here is why I got this pedal and if the sound doesn't absolutely blow your mind, if the once almost unobtainable guitar sounds from Deep Purples "Machine Head" arent compelling enough then there's simply no explaining to you why someone would want a treble boost pedal. It's much, much more than just a treble brightening circuit.

https://www.youtube.com/watch?v=awbV6HoG3cE
 

Tommy Biggs

Gold Supporting Member
Messages
6,494
You could just keep the gain low in the high input anyway. These are HUGELY versatile amps. I have no need to mod mine in any way.

Live, I usually have mine set at 4 on both volumes, high input for balls out rock.

For other types of music, I use the low input a lot. Gorgeous cleans from this amp.
With my bone stock 2204, the lower the gain (in the High gain channel) the greater the treble. I run my amp with the Treble and presence on 0 in the High Channel.

Try the low input - which is a much better pedal platform and is much more sensitive to the TMB controls. I agree that these are very versatile amps - but Brian May was running AC30s (and WEMs?) and Iommi ran Laneys - AFAIK, Blackmore ran Marshall Majors. All are pretty different from my beloved 2204.


I will say that these amps are noisy compared to some other amps I own too.
 

Schafrocks

Member
Messages
2,424
Why would you need a treble boost with one of the brightest amps made?

Get a Tube Screamer and Rockit!

Even a Graphic EQ Pedal would be a much better option
While I agree with this on many levels. A clean boost can give you a different tone than the TS. I used both for many years on my 800 and cover a ton of ground with those two. But the JCM's are very bright amps. But I love the brightness. One of the best amps made in the history of amps.
 

Pythonman

Member
Messages
409
Clip the bright cab, run the Hi input gain ~6, and play around with the Treble/Presence knobs.
You know, I was thinking of installing a push/pull on the gain knob to be able to switch in/out the bright cap. This is probably the best bet overall.

What possible advantages/disadvantages are there in removing C4, R5 and replacing with a 68Kohm resistor? I mean, does it really get you more gain or does it just make the low input into another high input?

Thanks for all the replies, it's much appreciated.
 




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