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  • Quote Originally Posted by m-theory
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    There are very concise, detailed instructions for that kit. Reading through that will likely answer all of your questions. Be mindful the B+ voltage you send to this board, however, based upon the limitations given in the instructions (150v to 350v max). My JCA20 has B+ 386v. You'll likely fry the mosfet with much more than 350v. Also, I'd swap those noisy, drifty carbon comp resistors with metal film, but that's just me.




    Is that why they were talking about putting a 2 watt 33k resistor in the B+ wire? I'm an electronics noob BTW..

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    • Is that why they were talking about putting a 2 watt 33k resistor in the B+ wire?



      That's a good assumption, though you may have to play with the value a bit, depending on where your rail voltage is. It seems as though it sways pretty widely, from what I've read and seen.








      I'm an electronics noob BTW..



      Be GD careful poking around inside there, then. Make sure you have it unplugged before you even open it up, and then make sure the caps are drained before poking around.

      Comment








      • Quote Originally Posted by m-theory
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        That's a good assumption, though you may have to play with the value a bit, depending on where your rail voltage is. It seems as though it sways pretty widely, from what I've read and seen.




        If mine were 386v, what would a 2 watt 33k resistor bring it down to?



        Also the instructions for that loop kit do not say where to place the "in" and "out" wires on the board for a JCA20H, that's why I was asking yall.. Does the following sound correct?



        Lift the end of R14 (a 470K resistor) that is headed towards VR3 on the board. Just unsolder that one leg of the resistor (on VR3 end), free it from the pad there. Now use the freed up pad there as the signal feed wire to the loop. The loop's return wire will connect to the freed end of the 470K resistor.

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        • If mine were 386v, what would a 2 watt 33k resistor bring it down to?



          Depends on the amount of current.








          Lift the end of R14 (a 470K resistor) that is headed towards VR3 on the board. Just unsolder that one leg of the resistor (on VR3 end), free it from the pad there. Now use the freed up pad there as the signal feed wire to the loop. The loop's return wire will connect to the freed end of the 470K resistor.



          That, or between the master volume and the coupling cap (C7)

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          • http://dl.dropbox.com/u/2816313/tune...x5sepmics1.mp3



            Updated with a new clip below (first test above): This time with an Apex 215 mic and I changed the mic placement. It leaves a lot of room for the bass guitar to fill in but not sure if there is too many highs??? Let me know your thoughts as I am tweaking for the best double-mic setup.



            http://dl.dropbox.com/u/2816313/tune...11mixdown6.mp3



            Thoughts anyone...

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            • Quote Originally Posted by m-theory
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              Wait a minute...you've modified YOUR JCA20 too, haven't you? Why didn't YOU go buy something else that would satisfy YOU, instead of spending YOUR time and money tweaking an amp YOU don't like?



              Personally, I can answer it, from my perspective...




              Well I liked the amp stock I originally just had the second channel wired up on a switch and when that switch is up the amp went back to stock. On the other hand a couple of posts back you told us that you "didn't care for" the stock amp.







              Quote Originally Posted by m-theory
              View Post

              First, I never subscribed to the religious adherence to stock anything, frankly. There's not much in terms of tone creating tools that I've found suits my personal tastes perfectly, right out of the box, and that's especially the case with regard to mass-produced anything.



              Secondly, I'm an epic cheapass. I LOVE being able to gig REALLY cheap amps that sound outstanding! Two of my regular gig amps cost me a grand total of $300 each, and I'd stand either one of them up against similarly voiced amps at any price. This JC has cost me a grand total of about $500, and is nothing short of astounding, imo. At the end of the day, this is all about what inspires US, right? So, if my heavily modified amps inspire ME, isn't that a "win?"










              Quote Originally Posted by m-theory
              View Post

              Finally, I not only get a huge kick out of doing this stuff, but I learn a lot about tone shaping along the way, and that's something that I consider well worth the tiny investment in time and money. I'd never have learned what I've learned about amps and pedals over the past 5 years or so if I'd have just bought stuff over the counter, only to later find that it wasn't quite what I'd hoped it would be anyway.



              Make any sense?




              Yeah. Keep on trucking man. If YOU like the outcome of what your doing then do it. All I offered was my opinion.







              Quote Originally Posted by TheEternal
              View Post

              Hey guys, on FX loop kits like this one here:



              http://www.mojotone.com/amp-parts/Mo...ube-Amplifiers



              Where would you break the signal and solder the "in" wire (from the amp PCB to the kit board) and "out" wire (from the kit board to the amp PCB)? I got this from another forum, but tell me if this would work..




              That's pretty pricey!

              See the schematic on page 7 of mojotone's pdf? You do it the same way as they show in that example. so if your gonna lift r14 the vr3 side is the in and the resistor is the out.

              As for your b+ measure the voltage at r 28 and report back before you do anything else. The black probe goes to ground and the red probe goes to the side of r 28 that is connected to r31 and c28.

              As for how much voltage a 33k resistor is going to drop use ohms law.

              http://www.aikenamps.com/OhmsLaw.htm
              Jca 50h/ 100h/ 22h Mod thread and Owners Club
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              • Just a taking a moment out of the normal tech posts to wish Jet City a happy birthday!!
                Jackson Infinity Pro/ESP The Mirage/Charvel Model 2
                Seymour Duncan Convertible/Carvin X100B/JCA100H

                Stewart

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                • If YOU like the outcome of what your doing then do it.



                  Back atcha, man. Glad your mods worked out for you, too. I really couldn't be happier with what I've got from mine.








                  wish Jet City a happy birthday!!



                  Very cool! Yeah, HB to JC!

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                  • The amp stock isn't bad. Enough there for me to judge how I might change/mod things. When I replaced the tubes for 60 bucks more I thought wow and for this price, you got to be kidding. Inspiring enough for me.

                    I have just one OD pedal and am looking on picking up a few more. All I really need for this amp is to bring out more grind and sustain for solos and I am happy. The OD pedal I have is a Damage Control Liquid Blues tube OD.

                    That and a Fish and chips gets me close to what I am looking for. Might try it with another cab I have laying around. So it really comes down to personal preference

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                    • Quote Originally Posted by jimmycantdance
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                      Just a taking a moment out of the normal tech posts to wish Jet City a happy birthday!!




                      This hbd jca. shine on you crazy diamond!
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                      • Quote Originally Posted by Mahuska
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                        The amp stock isn't bad. Enough there for me to judge how I might change/mod things. When I replaced the tubes for 60 bucks more I thought wow and for this price, you got to be kidding. Inspiring enough for me.

                        I have just one OD pedal and am looking on picking up a few more. All I really need for this amp is to bring out more grind and sustain for solos and I am happy. The OD pedal I have is a Damage Control Liquid Blues tube OD.

                        That and a Fish and chips gets me close to what I am looking for. Might try it with another cab I have laying around. So it really comes down to personal preference




                        What speaker are you using with it right now?
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                        • Wow. Step away for a few months and this thread just blows up!



                          I tried skimming through everything, but I didn't quite see what I was looking for, so I will ask it.



                          What is the best/most popular/best sounding effects loop kit for the original JCA20H. Looks like the bigs ones are the weber and the Metro.

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                          • Finally got the 'thrasher' mod installed (having a 4 month old to take care of really cuts into my free time). I didn't use the exact values the mod shows in a few places, but they're in the ballpark. Also got the hammond choke installed. All in all, definitely worth the money and time. About $23.00 and an hour to install Also got some new tubes. Since I'm looking for a higher gain sound I went with Chinese 12AX7B tubes in V1 and V2, with a Sovtek 12AX7LPS in V3. I've tried a bunch of different combos, but I always came back to these. Also got a new set of JJ EL84s for it too. Very happy camper. It's definitely got the sound I was looking for.
                            Peavey XXX (modded), Epiphone VJ (modded), Peavey Tour 450 (bass)
                            Mesa 412 (v30s), Greenback 112, G&K 410
                            Ibanez SZ320 (JB/Jazz), Ibanez RG3EX1 (Distortion/Jazz), '72 Hondo LP (stock Dimarzios), MIA Strat (stacked humbucker in bridge), LTD M107 (D-Activators), Agile PS-900 ('59/JB), Schecter Omen 8, SX Furrian tele, 'Fender' 5-string P-bass
                            Line 6 POD XT

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                            • I'm glad you liked the thrasher. any feed back? Did you figure out r32 alright?
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                              • Quote Originally Posted by Edge11
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                                I'm glad you liked the thrasher. any feed back? Did you figure out r32 alright?




                                Yep, got everything figured out the first time around. It sounds great. A lot more balls on the front end of the amp now. Hardest part of the mods was tracking down the choke
                                Peavey XXX (modded), Epiphone VJ (modded), Peavey Tour 450 (bass)
                                Mesa 412 (v30s), Greenback 112, G&K 410
                                Ibanez SZ320 (JB/Jazz), Ibanez RG3EX1 (Distortion/Jazz), '72 Hondo LP (stock Dimarzios), MIA Strat (stacked humbucker in bridge), LTD M107 (D-Activators), Agile PS-900 ('59/JB), Schecter Omen 8, SX Furrian tele, 'Fender' 5-string P-bass
                                Line 6 POD XT

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