Riffster Posted January 26, 2008 Share Posted January 26, 2008 Alright I am back on track. I am in the process of installing the effects loop on my EVJH and I want to be cautious not to place the jacks were I would get hiss or hum. I am trying to keep the FX loop close to the volume pot. Also I would like to move the amp main input jack to the left of were it is now, if I use a segment of instrument cable from the new jack to the PCB will this work? will it help shield the signal? Final question is: is there a way to shield cables inside an amp, meaning can the cables be wrapped with something that will kill slight hum? I have a version 2 but I get that faux tremolo effect once in a while, (probably due to my computer monitor and incandescent light) I am planning to re-arrange the cables inside the amp to try to avoid this...any suggestions would help.. Link to comment Share on other sites More sharing options...
cGil Posted January 26, 2008 Share Posted January 26, 2008 Yeah, everything works better with the shortest wires possible. The wire from the guitar input should be shielded, and the R2 resistor should stay right where it is on the pcb, connected directly to the control grid of the first preamp tube stage to help reduce noise. So just remove the modular connector from the board, and attach your new shielded input wire there. The center conductor and shield conductor of the wire should be connected at both the ends, to jack, and to the board. Use an isolated jack like a Cliff jack, not a Switchcraft jack. The jack is still the best place to attach R1. Recommended values for R1/R2 are 1M/68k respectively. As always, season to taste. For the loop and volume pot, you really only need shielded wire between the volume pot's center wiper and the control grid of the second preamp tube stage. Removing that modular connector is easier if you simply clip the soldered pins on the modular connector first. Then you can remove the connector and desolder the pins one at a time, without as much risk to the solder pads. Again, be sure to attach the shield conductor to ground at both ends, to the board, and the pot. As for the wire from the junction of R6/R7 to the loop jack and over to the volume pot can be unshielded, but keep them short, and close to the inside of the front panel wherever possible. You can shield these if you want and ground them to the volume pot's ground lug, OR to the ground end of R7, but NOT BOTH. Remember to ground the shield of this wire ONLY one end to avoid a ground loop. Also, when attaching the shield ground to the pot's solder lug, DON'T attach a jumper to the back of the pot because it's not a good idea to mix chassis ground and signal ground together at this point. Stick with the star ground topology and you can eliminate a lot of potential noise problems. Same reason behind using Cliff jacks. The pot-can should get its shield ground connection only from the chassis, so make sure you scrape off the paint inside the panel around the pot hole for good metal to metal contact. Gil... Link to comment Share on other sites More sharing options...
Riffster Posted February 19, 2008 Author Share Posted February 19, 2008 Well I finally got to this project, leisure travel and crazy storms have kept me busy...anyway I chickened out and made my mod but without even removing the PCB. I am happy with the result, no noise added at all. I left the amp stock of course with the exception of the loop, thanks again for all your advise Gil. I added the loop with separate send-return jacks, moved the input, erased the "input" lettering and the arrow on the volume control and most noticeably I installed a big a$$ knob. Here are a couple of pics... Link to comment Share on other sites More sharing options...
cGil Posted February 20, 2008 Share Posted February 20, 2008 Congrats! Good looking job, too! It's not so easy to get the holes drilled where they line up so well. Way to go! Gil... Link to comment Share on other sites More sharing options...
TWANG Posted February 20, 2008 Share Posted February 20, 2008 re: hole drilling. I found out, already. *G* What I did when they didn't line up quite right was make the hole a bit bigger and then move the thing so it centered before I tightened it down. But that only works if it's just a bit off. His look really good. congrats. That knob looks cool, too. Link to comment Share on other sites More sharing options...
Riffster Posted February 20, 2008 Author Share Posted February 20, 2008 Thanks for the cmpliments, I used the old trick of measuring twice and drilling once. I also used about 5 sizes of drill bits started with a real small hole and then gradually opened it, make sure the initial hole is exactly where you want it though... The original spot of the input always bothered me... I found an old post were you remove the R1 and solder it to the +/- on the input jack, is that right?. and then the removal of the JP1 I believe. Those are easy mods that I may do while I decide where to take it from there. Link to comment Share on other sites More sharing options...
TWANG Posted February 20, 2008 Share Posted February 20, 2008 R1 is 68K on some models. you want to change it to 1M for sure. and 1/2 watt or even 1watt. and on the input jack is supposed to be better. I gotta to that myself. R2 is right there so why not? I think 10K is the preference of most. (both to metal.. ) C1 and C2 aren't hard to do especially, and I found that though I thought Spragues would be it. I liked Mallorys better. Same as stock values. C3 and C4 are rather cheap, and everyone changes their values.. so I'd look into that, consider which guitar pups I'm using and swap them for sure. after that the addiction will take full hold and there's no turning back. Those are all cheap.. and fairly easy to get to, and once will probably do it for you, so .. consider! Link to comment Share on other sites More sharing options...
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