Actually that electro cap seems to be a cathode bypass cap. It boosts that stages gain (or for a smaller value cap it boosts highs). Taking it out lowers overal gain, but also lowers bass gain substantially. Also I'd twist those wires together, less noise.
WARNING: There is over 360 VDC in this chassis. EVEN AFTER YOU UNPLUG the amp!! HIGHER voltage is stored in the electrolytic capcitors...for YEARS after unpluging. Before ANY work, unplug the amp and use an INSULATED screwdriver to SHORT out the leads to the electrolytic caps; -usually they are all wired in parallel, but in class A there will be another cap near the output transformer. Good luck & remember this voltage CAN & WILL KILL you. I am a 40+ year HAM radio operator. BE CAREFUL.
I'd rather replace that cathode bypass cap with a smaller value, say .68u or .47u. That will make the tone more bright, but also give you the most gain at the frequencies of importance. You would dial back the "volume" (distortion, let's be honest) and find a more bright tone. The electrolytic there is really too big...it's giving gain to too low frequencies. If the jumper is clipped, that means gain is highly reduced in the preamp stage...so any good tone you are getting after is just from the power tube being over-driven...and nice thing in and of itself, if done in a pleasing way :)
Thanks for such a clear tutorial on how to do this mod. SUPER easy, done in 10 min (prob even less). I am leaving the switch out on mine b/c I def prefer this tone and don't think I will need to go back. But thanks for including. Now on to some more mods! Thanks again!
that capacitor is not on the output signal path of the valve and is not there to cut treble and gain. It is a cathode-bypass cap, and is there to INCREASE treble and gain, and if u cut the jumper u will get a decrease in treble and gain. When u think the switch is on, it is actually off.
Awesome! Thanks for posting this video, definitely going to try this on mine. *Edit* I got around to modding mine today, did it exactly how you did it and everything worked out great. Thanks again for the tutorial.
Cutting JP1 only removes the bypass cap from the first gain stage. Yes, it will make it sound "brighter" but only because you've adjusted the amount of bias being bypassed and removing fullness from the signal. You say "brighter" while I say "tinnier"... A far better mod (IMO) is to snip either end of R7 and lift the resister up on its side. This will remove that ground reference allowing for more signal to pass to the next stage. As the design stands, R7 is effective reducing the 1Meg volume pot down to 500k since it's in parallel. If you're feeling really crazy, you could solder a 220K in parallel with R6 and you'll REALLY get the signal pushing!
I did this mod today and to be honest it’s almost like a gain boost sounds different with my overdrive pedal, it’s a cool mod gives another flavour with the Amp !! I’ve owned some great amps and I can’t get over how great these are I have the version 3 great build speakers ok 👍
VJs are not "muddy" sounding...they sound like what you feed them with- guitars with humbuckers are "muddy" sounding, so, this amp will let you know that. they are fantastic little amps.
Yes a pot could be used in this location, but would need to replace the resistor and jumper or just the resistor or at least need a third location on the board to connect to. I would highly recommend looking for a schematic online, reading a book or two and working out the circuit on your own. I went on to trying to make my own 12v micro tube amp shortly after posting this vid(still working on it btw) and haven't really thought about this amp since it went to a friend almost 2 yrs ago.
@waarze1 It might be guitar. This jumper and corresponding resistor scrape higher frequency, cutting it should allow more to pass to the second pre-amp stage. If you're playing a "brighter" guitar like a Tele, etc. you might not notice the extra highs which could be overpowering the bottom end and making it "sound" quieter. I've found that I only use the mod at low volumes and others agree, w/other mods it sounds better loud with jumper in tact. Good luck and have fun.
@jak442 tried it with several guitars now: the hights are there! THANKS! but the thing i dont get is: how can the signal be reduced in volume when i interrupt the jumper to a grounded capacity. this is what my logics says... i might be totally wrong since i ve never done anything with technical electrics - i dont even know how its called^^ (since im not an english native speaker). but thanks anyays!
Just did the jp1 mod, but surprisingly I kinda lost some signal instead of getting some gain. I get almost the same sound with the mod and the volume at 10 as i get without the mod and volume around 6 or 7. How? Why? Any advice?
Actually that electro cap seems to be a cathode bypass cap. It boosts that stages gain (or for a smaller value cap it boosts highs). Taking it out lowers overal gain, but also lowers bass gain substantially. Also I'd twist those wires together, less noise.
WARNING: There is over 360 VDC in this chassis. EVEN AFTER YOU UNPLUG the amp!! HIGHER voltage is stored in the electrolytic capcitors...for YEARS after unpluging. Before ANY work, unplug the amp and use an INSULATED screwdriver to SHORT out the leads to the electrolytic caps; -usually they are all wired in parallel, but in class A there will be another cap near the output transformer. Good luck & remember this voltage CAN & WILL KILL you. I am a 40+ year HAM radio operator. BE CAREFUL.
I'd rather replace that cathode bypass cap with a smaller value, say .68u or .47u. That will make the tone more bright, but also give you the most gain at the frequencies of importance. You would dial back the "volume" (distortion, let's be honest) and find a more bright tone. The electrolytic there is really too big...it's giving gain to too low frequencies.
If the jumper is clipped, that means gain is highly reduced in the preamp stage...so any good tone you are getting after is just from the power tube being over-driven...and nice thing in and of itself, if done in a pleasing way :)
Thanks for such a clear tutorial on how to do this mod. SUPER easy, done in 10 min (prob even less). I am leaving the switch out on mine b/c I def prefer this tone and don't think I will need to go back. But thanks for including. Now on to some more mods! Thanks again!
that capacitor is not on the output signal path of the valve and is not there to cut treble and gain. It is a cathode-bypass cap, and is there to INCREASE treble and gain, and if u cut the jumper u will get a decrease in treble and gain. When u think the switch is on, it is actually off.
Awesome! Thanks for posting this video, definitely going to try this on mine.
*Edit* I got around to modding mine today, did it exactly how you did it and everything worked out great. Thanks again for the tutorial.
Cutting JP1 only removes the bypass cap from the first gain stage. Yes, it will make it sound "brighter" but only because you've adjusted the amount of bias being bypassed and removing fullness from the signal. You say "brighter" while I say "tinnier"... A far better mod (IMO) is to snip either end of R7 and lift the resister up on its side. This will remove that ground reference allowing for more signal to pass to the next stage. As the design stands, R7 is effective reducing the 1Meg volume pot down to 500k since it's in parallel. If you're feeling really crazy, you could solder a 220K in parallel with R6 and you'll REALLY get the signal pushing!
I did this mod today and to be honest it’s almost like a gain boost sounds different with my overdrive pedal, it’s a cool mod gives another flavour with the Amp !! I’ve owned some great amps and I can’t get over how great these are I have the version 3 great build speakers ok 👍
VJs are not "muddy" sounding...they sound like what you feed them with- guitars with humbuckers are "muddy" sounding, so, this amp will let you know that. they are fantastic little amps.
Yes a pot could be used in this location, but would need to replace the resistor and jumper or just the resistor or at least need a third location on the board to connect to. I would highly recommend looking for a schematic online, reading a book or two and working out the circuit on your own. I went on to trying to make my own 12v micro tube amp shortly after posting this vid(still working on it btw) and haven't really thought about this amp since it went to a friend almost 2 yrs ago.
@waarze1 It might be guitar. This jumper and corresponding resistor scrape higher frequency, cutting it should allow more to pass to the second pre-amp stage. If you're playing a "brighter" guitar like a Tele, etc. you might not notice the extra highs which could be overpowering the bottom end and making it "sound" quieter. I've found that I only use the mod at low volumes and others agree, w/other mods it sounds better loud with jumper in tact. Good luck and have fun.
At least you could advise people to discharge their caps with some 8+W 22kOhm+ resistors. It's better on the caps.
akkudakkupl The schematics ive seen show a bleed off resistor in circuit for that purpose.
nice, very good instructions; modded my EVJ myself
@jak442 tried it with several guitars now:
the hights are there! THANKS!
but the thing i dont get is: how can the signal be reduced in volume when i interrupt the jumper to a grounded capacity. this is what my logics says... i might be totally wrong since i ve never done anything with technical electrics - i dont even know how its called^^ (since im not an english native speaker).
but thanks anyays!
Just did the jp1 mod, but surprisingly I kinda lost some signal instead of getting some gain. I get almost the same sound with the mod and the volume at 10 as i get without the mod and volume around 6 or 7.
How? Why? Any advice?
Would that work? Your speaking my kind of language.