A dramatic amp mod as well as the simplest in the Epiphone Valve Junior Head Tube Guitar Amplifier is known as the “JP1 Mod”. The name derived from the jumper labeled JP1 on the board.
It basically morphs the tone of the guitar amp from one with no definition, dark, to an instant edgy and more present tone. To my ears things came to life using the Fender Telecaster compared to the raw un-modded amp I had.
And all this without even replacing the tubes that the amp is shipped with (Sovteks). I suggest replacing the tubes, to a JJ (former Tesla) set. From there things get serious. But at least now for the sake of seeing how much a simple mod like the JP1 can boost your Epiphone Valve Junior tone character.
Snip It!
That’s all it comes down to – snipping a jumper. Technically eliminating the C3 (22uF) electrolytic cathode capacitor from the circuit on the second half of the pre-amp tube (12AX7). Simple as that! The amp will start singing – but not in falsetto.
All the tool you need is a simple wire cutter (preferably a flat one). No soldering iron, no soldering skillz, NOTHING! You can do it! If you can clip your nails, you can snip the JP1 labelled jumper on your Epiphone Valve Junior.
Follow the steps in the video and report back with comments on your impressions. Good luck!
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Hello Gabi,
I watched your videos of both the unmodded amp, and after doing the JP1 mod.
I have to say, the amp you got sounded extremely bad to my ears. The thing is, far as I can tell from the numerous demos I have heard, Valve Juniors do not normally sound that bad. Not that they couldn’t stand some improvements, but that is not their normal out of the box sound.
Maybe it’s the sound quality of your videos. Maybe the Celestion Blue doesn’t go with the amp very well. But, I suspect you may have gotten a bad amp. We all know they use cheap components to keep the price down, and even I know that cheap components are inconsistent, which means the amps are probably a bit inconsistent as well.
I have a new, completely unmodded Vjr combo, and it sounds better than yours does even with the JP1 mod.
So does the one in this video–stock VJr head and cab, US Telecaster Standard, no effects, with some pretty cool playing (and pretty funny too. Check out the “decoration” sitting on top of the amp head)–which shows what this amp should sound like out of the box:
http://www.youtube.com/watch?v=NJByqsSExgw
Perhaps if you want to accurately represent the Valve Junior and the mods that you do to it, you should start with an amp that isn’t a lemon in the first place. On the other hand, maybe starting out with a bad one will show viewers that even if they get a lemon, there is hope.
In any case, if the JP1 mod improved your horrible sounding head, it ought to make my pretty decent sounding combo really shine!
Now, where’s those clippers…
Hey Gabi! Been reading about the JP1 mod (did it to my EVJ head a while back) and other things people are trying. I have found that the amp has so little head room that it hasn’t been as ideal for what I’m looking for (which is a clean-to-slightly overdriven tone). One option I’ve tried is switching out the preamp tube for an AT7. It’s still quick to break up, so I’m contemplating an AY7 to bring the output down even more from the preamp stage. I’ve been considering all the many mod kits out there like Bitmo and Watts Tube Audio. Overall, I’d like to brighten the tone and create more head room so that it can be more versatile. Any thoughts would be greatly appreciated!
Hey Gabi,
So I have the V3 combo, and I did the JP-1 mod and love the new clarity.
One question though: Now, with the volume on the amp completely off, I can hear my guitar signal very faintly. What’s up with that? It seems somewhat fizzy and distorted. I didn’t do anything wrong did I?
Hi Sam – Very sorry for the delay. Hmmm… that’s strange. Not sure why. Need to test that on mine.
Hi Matt – Sorry for the delay.
I suspect playing with the cathode resistors (R8 and R9) and their respective plate resistors (R3 and R4) on each half of the preamp tube would do the trick. Version 3 has a typical Fender biasing (100k anode and 1k5 cathode), check if this is the case. In other words you should have:
R3 – 100k / R8 – 1k5
R4 – 100k / R9 – 1k5
Matt – that’s the part I have already documented in my upcoming video. Considering that we can wire a negative feedback, you can insert a Presence or Resonance control if you wish, really easy.