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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Hi Gabi,About the JP1 mod?..Did you not say somthing about a Presence switch?..and/or..what would happen if i added a switch to the JP1 jumper or a pot or a dpdt switch and a pot?yhanks..Mark
hey, i had done the the JP1 mod and it mad the the sound so much better thanks for your tip. i was woundering if you would post a video up on making the epiphone have more power buy adding more tubes or adding a slave out put to run in to different head or for recording. thanks for your time.
brandon
Mark: That’s precisely next on my table. Morphing that simple JP1 mod into a Presence or Resonance control (switcheable, a dpdt pot in fact).
Brandon: Your are welcome! Adding more power to the Epiphone is more of an advanced tutorial and I will probably make it available later on. For now I am trying to concentrate as much as I can on very simple mods that will have a dramatic effect. Stay tuned. I am also learning as I go. Much fun!
Thanks for the comments, guys! It is good to know that someone actually reads my blog posts
Does this mod work on the combo version?
Thanks
B
B: It should although I heard one report of the amp going silent. Not sure if that was because of an obscure board version we didn’t hear of, or simply the user snipped the wrong jumper.
Thanks!
Gabi.
Dear Gabi:
What a nice simple mod. My VJ sounds much less constipated. Watts Tube Audio (turretboards.com) has a list of how to identify the circuit boards. Mine looks like yours and is a version 3. I purchased this rig to mod and you got me off my ass ; thank you. I will be exchanging some tubes as I have some early seventies Telfunkens. I also use a GNX4 and the Epiphone cabinet speaker and you can get some ear bleeding volume at much less than half on. I am looking at changing the output xformer do you believe that this will have a very significant effect on tone?
I think I can shed some light on the case of the silent amp- I just tried this mod on my VJ combo and also ended up with no guitar signal passing through (although to be fair, it also reduced the background noise considerably
). It was definitely JP1 that I cut.
Mine is a V1 circuit, which is laid out on the PCB very differently to the V3 you show in your Youtube video, so it wouldn’t surprise me if JP1 is some other part of the circuit. In any case, I guess this is a likely explanation for the problem the other guy experienced…
Thanks Bob!!!
That indeed sheds BIG LIGHT! Thanks so much for the feedback! That narrows down my searches for the versions of the board. Excellent tip!
Now if any of you have a V1 picture of the board – top and bottom – send it over and I’ll try to solve the mysterious problem…
Thanks a TON!
Gabi.
Bluewail: Absolutely the change of the output transformer will make a huge difference. There are many options out there but the most popular are the Hammond 125DSE and ESE OT’s.
I am planning on a OT replacement video one day also.
Gab
Great video! I have a V3 head, and I’ll be snipping JP1 when I get home! For a “presence” control, would it be as simple as soldering in an audio pot in place of the jumper? If so, any recommendations (250K vs 500K, etc)?
This was a great video —
I just got a combo with an eminence speaker…I am a little confused about the steps to do on the combo verses the Amp head.
So First question. How do you determine a V1 from V3 ?
Second question: If my Combo is V3 do I just follow the same steps as your video?
Third Question: If mine is a V1 do I just seek out the JP1 Jumper and snip it
Last Question : Should I just wait?
Dumb questions but help is appreciated.
Also I am looking forwards to your presentation on a presence switch
Thanks
Paul
hello!
great mod!
is it possible to make this “jumper cut” switchable by a normal little switch? i think that after cutting the jumper i can connect its loose sides to the 2 (out of 3) pins of a normal switch.
is it safe to use the switch while the amp is operating?
do i need a heavy duty switch?
thanks!
Paul – Sorry for my delay – too much time spent in the shop these days.
Q1: V1 boards are green, and were designed to have axial filter capacitors as opposed to radials on v2 and v3 boards.
And to quote Gil from the Sewatt.com:
“But how can you tell one amp from another? Easy. Only version 3 Valve Jr’s have a black printed circuit board. V3 VJr’s have no “I O” lettering on the power switch. They also have 16 or more numerals in the serial number (older models had 8 or 9 numbers).
And they have a 5k OT. The iron is always labeled on top with the color code and impedance (voltage for PT) data in all versions.
All v1 and v2 VJr’s have an “I O” on the red power switch, they have the 7.5k OT, and blue 12v taps on the PT. They both have green pc boards, but the v1 VJr’s had a board designed for axial filter caps. They came equipped with radial caps with the leads stretched out across the board. The v1 amp also hums like crazy from AC heaters and insufficient filtering in the power supply (no reservoir cap filter node).
Here’s a site with a full shot of the v1 pcb about halfway down the page.. http://duhvoodooman.com/VJr/VJr_mods.htm -”
Q2: Yep – the instructions of the JUMPY mod in this post should apply on a V3 amp (all black)
Q3: This “JUMPY” mod will not work on a V1 board. See how to apply this mod in a V1 case in this Sewatt.com discussion here.
irakliszs:
It is definitely. Actually if you give me a couple more days, I will post a video on how to enhance this JUMPY mod to a more elevated Presence potentiometer that also is switchable so you can switch the jumper on or off – quite cool! Yep – you can switch it on and off while the amp is operating.
Gabi
Hi there!
This might be a silly question, but as far as I can figure we’ve established, that the JUMPY mod apblies to the v3 and NOT to the v1 of the amp. But what about the v2? Can the mod be done to that?
Best regards!
Oh… and it’s a v2 combo, by the way!
Hi!
Just did this simple but yet great mod to my head and now it sounds great.
When will you post the tutorial on making it switchable?
Max
grat mod and video Gabi! My buddy tried it as well with great results! After a year of mud even with new jj tubes and a great tone shaping pedal,I got on it and did the mod ’bout a week ago. Huge improvement! I have great tonality(more cleans at a better volume and less bass in my face!, and can get the majority of the drive back with my direct drive pedal. Sounds great as all pick up positions sound usable (instead of bridge HB and bridge coil tap only somewhat usable as before mod). thanks!
Hey Gabriel,
just stumbled upon your wedsite and checked out your video about the jumper mod…
its really excellent…
i bought my vj two weeks ago and already had a few plans to mod it… problem was i dont have a soldering iron here yet and all the other tools are at my dads place. and i wont be going there for the next month.
so i opened my amp (i have the combo version) and cut the jp1 (with a pair of surgical sissors, that worked too=) and the result is brilliant.
not only is the sound more defined and less muddy, the whole amp doesnt sound as boxy anymore (i also experienced that it doesnt break up as early as it did before, but if it does it a much thicker crunch).
looking forward to the negative feedback and presence mod you were talkning about in your video…
thank you very much.
Olion
just read the thread, can hardly contain myself.cant wait to hear my head after the snip……will let you know. thanks
exxxxxelent, that puts a bit of sting in the swing!! for clarity, my head appears to be a v2 model, green bcp, 7.5k ot ,same layout as the black one in the video. i played with a alligator jumper for a minute to see if i wanted to put a switch on and decided….mmmm nope , i like it just like it is. if ya do want to put one on, a spst would work i think…..thanks gabi, nice goin!!
Gabi…MANY thanks. Very simple and excellent mod. Took all of 10 minutes from start to finish. My V3 head is now much more articulate and sounds great! Thanks again and keep the videos coming!
Hans:
I’d say give it a try even if it is V2. Let us know if it worked. If not, just solder the jumper back in the place you snipped it.
Max:
Very glad to hear it worked! I am slowly getting to the video on how to insert a switchable potentiometer in place of the jumper. Will give much flexibility to it. Stay tuned.
John Price:
Sooper! Interesting to hear that now all your pickup positions are now usable. It is almost like the jumper cut breathes new life into the thing. Incredible! Thanks for the report!
Olion:
Thanks for the comment! That is the first combo I hear of where the JP1 mod worked! It means that you have a newer version of the board in there (possibly v3 or higher). What year is you amp?
c.a.r. boy:
Thanks for the feedback! So your success confirms (or at least comes close) that the mod will work on version 2 boards as well! And yes – why would one go back to the un-modded version once it tastes of the great tone? But indeed a SPST will work for those who really want to go back.
John Dye:
Thanks for the feedback! Isn’t it amazing how such a simple mod opens up the whole tone!
Hi Gabi,
Just finished the jp1 mod and I am amazed at the results (version 3 head)! More bite and bye bye mud! I was not happy with the stock tone and I was about to gut it and build another amp in it’s chassis. BUT I had to try this mod before all that work…and I am glad i did.
Being a father and a husband with a large “Honey-Do” list, your simple mod was quick to implement and really got me to appreciate this little amp head better. There are a ton of mods out there, many are overkill. There is no easier method of correcting the stock mud than the jp1 mod. For those of us that don’t want to solder for hours on end searching for the right vj tone, you have to do this mod!
Peter Garcia, Oak Park, IL
Peter! This is great news! Thanks for the great tone report! I hear you with the “Honey-Do” list. I wish I would find a quick mod for that! Lol…
Glad to hear the mod was of help!!
Cheers!
I’ve been making some non-invasive tweaks over the time I’ve had my V3 head and cabinet. I swapped out tubes, which cleaned up the sound a bit, then I swapped the Eminence speaker for a Celestion (which I bought from Gabi…awesome service and prices, check it out!) But finally, after much indecision, I finally did the deed…snipped JP1. Geez, thats a tiny little wire in a tight spot! Before I get into my review of the effect, let it be known that I’m going to put in a little SPST switch this weekend, so I can do a real comparison of before vs after.
First impressions were mixed, frankly. I have a heavily modded Squier Strat, with a single coil at the neck, and a bridge humbucker. The improvement on the single-coil with the Jumpy mod was big, even to my untrained ears. Much more robust…the word that keeps coming to mind is “throaty”…whatever that means. That single-coil just sounded like it got angry, in a good way. However, the humbucker on the bridge seemed a bit more gain-y, but it didn’t seem to come to life at all. I pulled out my semi-hollowbody, with two humbuckers, and it was the same…just didn’t give me any added clarity or depth.
Again, I’ve got the switch ready to go, and I’ll follow-up when I can do a proper A/B with it. There’s other tone mods out there, but I’m not overly confident in my soldering skills yet, so I want to give JP1 a full trial before I consider something else. If anyone has any insights, please post…thanks!
Hey Gabi,
I gave it a shot on my V2 and…….it’s amazing! First it’s great that your mod worked because I wasn’t shure anout the V2 and second: The sound opened up just like everybody said.
Thanks,
Merlijn
Hey gabi!
I just bought the VJ. I just need a ceb now xD
and about the jp1 mod, won’t the max volume drop?
(bad english) and which tubes would you recomend for less gain
and high volume?
Cheerz
Okay…I installed a switch (I put it in the back, just in case I did an ugly installation job), and NOW I can properly hear the difference. I still have the improvement in the single-coil, and I can tell there’s definitely an upgrade in the clarity of the humbuckers. Its not enormous, but its real. I still get a very slight increase in gain with JP1 cut…not sure why that would be…probably less reistance somewhere.
Now that I have the switch in, I really don’t need it! I’m keeping Jumpy!
I replaced the output xformer with the Heyboer and installed Switchcraft jacks, except for the input. I used a switch for the Jumpy mod and it sounds great. The use of a switch allows me to use more mutted Jazz tones. Half on will run everyone out of the house, assuming hats what you want to do. I have a valve special and I am wondering if they use a similar topology for the circuit board, Because this amp has a second valve to drive the effects I would like to overdrive the input preamp and a similar cathode cap bypass will hopefully do the trick?
Thanks Gabi
I will report on additional mods I have planned.
So when do you think you can get around to the next mod? Its been a year.
yea, can you post some other easy mods?
Thanks!
Jim:
Thanks a lot for your in-debth tone report on the Jumpy mod. Yes – I had the same impressions on my single coil. Much more pronounces attack also.
Also was good to hear of your switch experience – it helps A/B-ing the mod but in the end one will leave it always off.
Merlijn:
Glad to hear it worked on your V2!! Will keep it for the record! Way to go!
Jordi:
Not sure what to say. I would recommend JJ tubes, but really it comes down to trying a few brands and hear how it sounds.
And yes, I have a couple easy mods (variations of the Jumpy Mod) lined up. I only need to find the time.
Thanks for the comments!
Bluewail:
Thanks for commenting! Not sure what to say about the Valve Special. I might need to check that out one day. I could tell your from a schematic comparison. And yes, please let me know of those mods.
Dave:
I know it is getting late, bro. Hang in there it’ll come. Need some time to actually sit down and start modding. But I’ll get to it, no worries.
Hey so doing my own research I’ve found that this JP-1 mod is the first step to installing a Negative Feedback Switch I believe (so you can go back and fourth between the 2 tones?? I’m assuming) Anyways I was wondering if you could help me out by putting up a video on how to not electrocute myself when doing amp mods, aka discharging the capacitors. It seems like the most dangerous part and yet there is little visual help out there. I would appreciate it. Also I just purchased an ebook with maybe 7 various mods for the EPJ. Perhaps I could share it with you and we could mod this baby simultaneously? Let me know what you think.
Hi Dave!
Thanks for writing. Here’s a whole post on safety when working with amps you might find helpful. The main thing you should use is common sense, and making sure that the amp is not plugged in while you are working.
And yes the Negative Feedback is a continuation of this simple Jumpy Mod – I hope to get soon to that video, time permitting. I’d be very curious to know of the mods from that ebook!! Sure send them along to me, and I could add them in my next video!!!
Hey. Hoping you can help me out. I have a Version 3 Valve Jr. Combo with a black board. It matches the one in your instructional video. I snipped the JP1 wire (positive it wasn’t JP2) and bent the wires up. Before I put the amp back together I plugged it in, connected the speaker, and plugged in a guitar to see if it worked. The power switch lights up, but there is no output. The tubes don’t even warm up. I was very careful not to touch anything other than the JP1 wire while I did the mod. I bent the wires back togther so they are touching, and still no output or warming up of tubes. Is there something I’m missing?
The amp is brand new as of yesterday. I hope we can figure this out. Thanks.
hey gabbi sorry to bother you AGAIN, but I was thinking about the NFB mod. Are you planning on hooking up a switch so you can more or less on/off it, or are you going to put in a pot so you can dial in as much as you need?
Hi Dan,
Sorry for the delay. That’s strange. So the only “operation” you did was cutting the JP1? If this was an earlier board version that didn’t support the mod, having it re-done (JP1 jumper soldered back together) should have make it work again.
When you say ‘tubes don’t warm up’ they don’t even light up? Is there any way you can solder the two snipped of the JP1 back together?
let me know.
Hi David!
Yes – in fact more than a switch. A switchable potentiometer that lets you dial in the amount of what you need. I just need to drag myself to the shop and actually do it. Lol
Gabi,
Thanks for getting back to me. I spent a bunch of time looking through forums and the guys over as http://www.sewatt.com ended up helping me out. It turns out that the culprit was a bad contact on the fuse. The contacts need to be scored so that they make better contact. Contact cleaner alone didn’t work for me; I ended up using a nail file to score the surface, which brought the amp back to life.
As far as the mod, it opened the amp up a bit, but it’s still REALLY dark.
Dan
Hey Dan,
I just got an upgrade kit from fromel electronics. I haven’t had a chance to install it but supposedly replacing one of the stock components is really supposed to brighten this amp up. If you feel like emailing me I’ll let you in on the info and you can decided for yourself if you want to try it.
guycalleddave@hotmail.com
the mod is a 47pf cap across the mid and left pin of the volume pot. supposedly brightens up the amp at low volumes and looses its effect as you turn up the volume.