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Peavey JSX Mod Question


maggotspawn

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maybe it's been a while since I've played one but I do not recall those things lacking in gain in any shape. In fact, I recall thinking it was an amazing amp bone stock and would really only consider a transformer upgrade to improve articulation.

 

I wouldn't mod it unless you know what you're doing, but I think Drakkar either had his modded or modded it, I can't recall which but he could probably point you in the right direction.

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maybe it's been a while since I've played one but I do not recall those things lacking in gain in any shape. In fact, I recall thinking it was an amazing amp bone stock and would really only consider a transformer upgrade to improve articulation.


I wouldn't mod it unless you know what you're doing, but I think Drakkar either had his modded or modded it, I can't recall which but he could probably point you in the right direction.

 

 

OP is saying it's lacking gain compared to the XXX, not in general. Drak had FJA mod it and uses KT90s I believe.

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OP is saying it's lacking gain compared to the XXX, not in general. Drak had FJA mod it and uses KT90s I believe.

 

 

yeah, still wasn't my experience that it lacked gain compared to the XXX, maybe I just played a crappy XXX.

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I actually just played a jsx and xxx side by side at a music store today. The xxx is a little more compressed cause of the extra gain, but compressed in a good way. Kinda has a fuller sound. The ultra channel on the jsx is close to the crunch on the xxx but still not quit the same. I personally like both the gain channels on the xxx but then again I used to own one so I am pretty familiar with how to tweak it. A while back I found some info about modding the jsx to xxx. Below is the copy and paste:

 

Peavey jsx/xxx/ultra differences 2

 

the differences between the JSX and XXX/Ultra series are small, but meaningful.

 

JSX R6/56k

 

XXX R6/220k

 

(JSX drops way more gain to ground)

 

JSX C35/10nF

 

XXX C35/22nF

 

(JSX boosts frequencies above 10k, XXX boosts lower)

 

I also found this about the tone stack:

 

FYI to turn the JSX tone stack into an XXX tone stack:

 

Crunch

 

remove R16 R106 C67

 

Ultra

 

remove R107

 

switch R44 240k ->220k (subtle!)

 

 

 

I am not too sure about the tone stack info, but the gain part seems about right. I remember looking into the schematics about it.

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I actually just played a jsx and xxx side by side at a music store today. The xxx is a little more compressed cause of the extra gain, but compressed in a good way. Kinda has a fuller sound. The ultra channel on the jsx is close to the crunch on the xxx but still not quit the same. I personally like both the gain channels on the xxx but then again I used to own one so I am pretty familiar with how to tweak it. A while back I found some info about modding the jsx to xxx. Below is the copy and paste:


Peavey jsx/xxx/ultra differences 2


the differences between the JSX and XXX/Ultra series are small, but meaningful.


JSX R6/56k


XXX R6/220k


(JSX drops way more gain to ground)


JSX C35/10nF


XXX C35/22nF


(JSX boosts frequencies above 10k, XXX boosts lower)


I also found this about the tone stack:


FYI to turn the JSX tone stack into an XXX tone stack:


Crunch


remove R16 R106 C67


Ultra


remove R107


switch R44 240k ->220k (subtle!)




I am not too sure about the tone stack info, but the gain part seems about right. I remember looking into the schematics about it.

 

This helps a bunch. I really like the JSX a lot, it could just use a hair more gain on the crunch channel to be perfect for me. Thanks everyone.

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I know others have said this but,.. BE VERY CAREFUL when working in amps. It can have deadly current even when unplugged from the outlet.

As far as added gain I do wanna mention something. Others are right about the jsx have plenty of gain, it just doesnt have the saturation that the xxx has. Also, the difference between the jsx and xxx is not just gain. The tone stack is a little different, even tho they both have active eq there controls respond differently from each other. the xxx seems to have a bigger sweep. The differences in components is very few but they go a long way. Just wanted to throw that out there in case you think that just adding the gain back will give you the xxx crunch.

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Just get high gain preamp tubes..seriously. The JSX does have less gain than the XXX, but the XXX has a stupid amount. The JSX has an actual useable sweep. Hotter pickups, a boost, and high gain preamp tubes do the trick.

 

 

And yes..I had my modded with more gain, but truth be told it was far too much so I use 12AT7s to tame the gain

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Also what most people don't mention is that the JSX has two versions, one bright one darker (like the ...valveking does) and peavey hasn't called them revisions or anything. The peavey forum have the details to recognise them. Some even put a passive tonestack, 5150 style on the JSX and sounds great. I really like the crunch channel on the small XXX 40 which has a normal passive tonestack, crancked with high output guitars through a good cab better than all the other variations. It has its own thing going.

 

Cool amps!

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  • 4 years later...
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I had to raise this thread from the dead.

I feel physically ill. I took my JSX in to get it modded with the mod listed in this thread. A cap, a resistor and a gain pot. I didn't mess with the tone stack. I looked at schematics of both the JSX and the XXX. The mod looked promising. Got the amp back, and it has no balls at all. It has less gain on the Crunch and Ultra channels then it did before. The shop that modded it felt sorry for me and are going to change it back for free. I'm still out $175, and I'm praying they can get it back to how it was.

 

tl;dr Had my JSX modded and now it's screwed.

 

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