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  • Also can anyone give me a heads up to which resistor and cap numbers (i.e. R9 C2 for example), effect gain, treble, mids, and bass just to help narrow down where to focus when mods are performed. Thanks again!

    Comment


    • ewizard
      ewizard commented
      Editing a comment

      For noise and longevity, larger wattage resistors are quieter and will last longer than those of lower wattage ratings. I.E. A 1 watt resistor will be quieter and last longer than a 1/2 watt will. Metal film is quieter than carbon composition, sounds a little bit different ( some say sterile and dry ? ) and is usually closer in tolerance ( 2% instaed of the usual 5-10% used for carbon comp. ). 

       

      As for capacitors, each one sounds a little different as should be expected considering that there are several types of the same value a lot of the time. Ceramic, tantalum, oil in paper and all the other types will have a varying degree of impact on sound. I don't feel that one is truly better than the other, or that changing only a few out will make a huge impact on sound. The voltage is important though!!!!!! You can run as high a voltage rating as you want, or can fit. You cannot however replace the current capacitor with one of a lower voltage rating. A stock capacitor that is rated for 400V must be replaced by one that is 400V or higher. 600V is the next highest voltage rating and the higher the voltage rating the larger the capacitor will be. The larger the voltage rating the longer the capacitor will last! The voltage rating is more about service life than actual voltage capability. If you replace the current capacitor with one of a lower rating, it will work just fine; for only or a short period of time though!!!!!! Going larger will not change the sound, but will ensure that the capacitor will not fail for a very long time. 


  • These changes will do a lot to get a nicer, tighter sound and reduce flubbyness. To archieve even more clarity and openness on the 22H, just swap out R9 (this 1M parallel to C5). This is one of the best things, you can do to this amp. Sounds way better with more definition and a clearer bass.

    What value on R9? I have 470k on both R9 and R5.

    Comment


    • Ok so after some reading here:  Modifying Preamp Circuitry

      I did 2 simple mods that brought the 22h right where I wanted it.

      after trying to reduce the squishy bass at R9 I noticed it didn't do exactly what I expected, after reading the link I posted and how R9 is in the coupling circuits decreasing this value just adds more gain going to the second stage it explained alot. so here is what I did, i swapped r6 with r24 and swapped r16 with r26. now this amp sounds the way I expected it to sound and I didn't have buy any more resistors or caps, just used what was available. from what I could tell I swapped R6 with with R13 and noticed the bass in the crunch channel was less squishy but the OD channel had more of a fuzz type gain which I then swapped with R13 with R14 not much better. so that made me want to have both plate resistors(R6-7,R13-14) to be the same value as it is in a marshall 800 all at 100k. this helps the bass response taking squish  to tight-sag, and tighter as you turn up the volume. I can now dime all the tone controlls and set the presence at 0-5. very nice! With the mids at mid point very very nice! scooped mids has more of a Mesa sound imo.  next is to just add a fixed resonance mod

      Comment


      • whiskeyjamboree
        whiskeyjamboree commented
        Editing a comment

        That link is not working and I like what you are describing. Is it possible you can put it in long form so that I too may read.


    • Footswitch wiring.

      Just thought I'd post this here for anyone interested. I bought my 22h used and it had no footswitch.

      Emailed them (Jet City) and they told me a generic Marshall style would work. Which it did, but seeing as the amp has no channel indicator on it I wanted on with an LED.

      That one didn't work right. After some investigation and re-wiring I've got it now. You can find these Marshall footswitches on Amazon and eBay for about 14 bucks and just rewire them.

       

      As you can see the original "Marshall" wiring the LED is in parallel. This doesn't work on the 22H. (Only had a jack on the schematic program, no plug. Switch comes with a cord soldered in it.)

      JCA22Hfootswitchwiring.png

       

      As a side note, I was going to mod my amp too but then I bought a different cab and speaker and now it sounds great. Got a vintage 30 celestion in it. I know some guys don't like them but I think it sounds great with it.

      Attached Files

      Comment


      • haircut
        haircut commented
        Editing a comment

        RictusGrin wrote:

        Footswitch wiring.

        Just thought I'd post this here for anyone interested. I bought my 22h used and it had no footswitch.

        Emailed them (Jet City) and they told me a generic Marshall style would work. Which it did, but seeing as the amp has no channel indicator on it I wanted on with an LED.

        That one didn't work right. After some investigation and re-wiring I've got it now. You can find these Marshall footswitches on Amazon and eBay for about 14 bucks and just rewire them.

         

        As you can see the original "Marshall" wiring the LED is in parallel. This doesn't work on the 22H. (Only had a jack on the schematic program, no plug. Switch comes with a cord soldered in it.)

        JCA22Hfootswitchwiring.png

         

        As a side note, I was going to mod my amp too but then I bought a different cab and speaker and now it sounds great. Got a vintage 30 celestion in it. I know some guys don't like them but I think it sounds great with it.


        Don't know why the "original wiring" above did not work for you because that circuit is exactly the same as my Jet City JCA22H footswitch. It works by shorting the jack's Tip to Shank (Gnd) to energise the channel switching relays RLY1 and RLY2 to switch to the Crunch channel.

        Overdrive channel = Tip - R - LED - Shank

        Crunch channel = Tip - Shank (Short circuit)

        And your "working wiring" circuit does exactly the same thing too (as far as the JCA22H is concerned). You've just open circuited the resistor and LED instead of short circuiting them in Crunch mode, but it really makes no difference.

        Glad you got it working anyway.

         

        I'm planning on adding a switch to the front panel to switch channels because I prefer that to using a footswitch. I'm still undecided whether I'm going to drill a hole for a toggle, or replace the standby switch with a dual rocker, or just replace the standby altogether.

        All you need to do then is bring a wire to the switch from the footswitch jack's Tip. And then just wire it up like the footswitch - Overdrive takes it through a resistor and LED to Gnd and Crunch just shorts it to Gnd.

        (BTW the resistor in the JC footswitch is 68k.)

         

        P.S. I should add that on the JCA22H BLOCK DIAGRAM that I got from JC, the circuits for both the footswitch and the head's footswitch jack socket are totally wrong. The footswitch is actually as described above and the jack socket is simply Tip to the relays and Shank to Gnd. It's Mono not Stereo type and the switched side is connected to the normal side, so nothing is actually switched when a plug is inserted.

        Attached Files

    • Does anybody saw that video:

      I'd love to know what mods they did to get that "vintage sound", to do something like that in my JCM 22 (less gain, slightly darker, ....). I did some mods on my 22, but still could not get the sound I want (closer but not quite there).png" alt=":smileyfrustrated:" title="Smiley Frustrated" />

      Comment


      • Jase01
        Jase01 commented
        Editing a comment
        Hello, I haven't been back here for ages and have pretty much forgotten what I learnt while I was here!! Hahaha
        Anyway, I did the mod to increase gain on the crunch channel and made it switchable. Sounds great and from bad memory, easy to do. Anyway, why I'm back is I'd like to do something similar with the OD channel, for a more full tilt "METAL" sound. Does anyone know how this could be achieved?
        Also is there an internal power source I can tap to run some LED's for some bling?

        Cheers

    • Hi everyone!

      I know this isn't the "introduction" thread, but I'm a long time guitar player, and brand new JCA22H owner. I'm new to HC and have gleaned a good amount of knowledge about the 22H from this and other forums. I'm a pinsetter (bowling machine) mechanic by trade, but am just starting to learn about the electronics contained inside a tube amp.

      I've successfully done a "JCA to SLO" mod on mine already (easy enough), but I only followed someone else's directions without really knowing exactly what I was doing and why it worked. I'm really looking to get up to speed on the workings of this amp, and I guess I've got an increasing interest in learning guitar/amp repair and modding. Can anybody recommend a good web site or book that kind of breaks everything down into manageable pieces? I'm looking around on Amazon right now, any recommendations?

      Anyway, thanks in advance, and I hope to be able to start contributing here in the near future!

      Comment


      • Soulcrusher_X
        Soulcrusher_X commented
        Editing a comment

        thebuch wrote:

        Hi everyone!

        I know this isn't the "introduction" thread, but I'm a long time guitar player, and brand new JCA22H owner. I'm new to HC and have gleaned a good amount of knowledge about the 22H from this and other forums. I'm a pinsetter (bowling machine) mechanic by trade, but am just starting to learn about the electronics contained inside a tube amp.

        I've successfully done a "JCA to SLO" mod on mine already (easy enough), but I only followed someone else's directions without really knowing exactly what I was doing and why it worked. I'm really looking to get up to speed on the workings of this amp, and I guess I've got an increasing interest in learning guitar/amp repair and modding. Can anybody recommend a good web site or book that kind of breaks everything down into manageable pieces? I'm looking around on Amazon right now, any recommendations?

        Anyway, thanks in advance, and I hope to be able to start contributing here in the near future!



        Merlin Blencowe has a few good books out there as well as Kevin O'Connor. I think both can be had on Amazon. Google the name Randall Aiken for some good tech articles. Also, you may want to sign up for the SLO Clone forums. There are lots of folks there to learn lots from. Also, come over to the GuitarAmpBoard in GRIMESPACE sig. There are a few threads on JCA mods and tips. I am Jay over there.


    • Pulling tubes !

      What's your experience with that ?

      I have tried yesterday on my jca100, removed the 2 outer tubes, and i am quite impressed by the results.

      ithe amp does not get quieter (still loud as f...k) but it sounds... different! Bass frequencies are less invasive and the sound is less "rich", more middy and a little bit stiffer, in a good way.

      I think i will leave like that for the moment.

      So, do you think I have to rebias it ? I am reading 453V beetween pins 3 and 8 and the old bias was 35mA

      See ya

       

      Comment


      • GRIMESPACE
        GRIMESPACE commented
        Editing a comment

        Did you change your speaker connection? IIRC, you should be using the output jack that is 1/2 of what your load is - a 16 ohm cab would plug into the 8 ohm output, and an 8 ohm cab would plug into the 4. If you didn't change the connection, that may account for the difference in tone.


    • I did the Predator mod as laid out on page 20. I have the right value for C2 so that is not an issue. I have the service manual and matched up voltages. 

       

      Here are my problems-

      1. The 2nd channel is now working at about 1/10th volume and headroom as stock. I can turn the master all the way up. It is also clean until 7-8 on the OD gain knob. 

       

      I was thinking that I must have purchased a resistor much lower in value than listed to explain this, though I double checked my order and component swap list (which seems fine). HELP!!!

      Comment


      • thechamp
        thechamp commented
        Editing a comment

        The problem may be the 3.3uf capacitor being in reversed polarity +/-. I will switch this when I get home in an hour and give an update. This is the only cap I have with two different color legs. My guess is this is the only one where it matters which way it is set in.

         

        Update:

        I played around with this for a few hours today to no avail. I am really frickin pissed off right now because I cannot get this to work. I have no idea what I'm doing wrong. I looked at a color code chart for resistors but it is about calculating values, not +/- like battery placement in a fixture. Wish I could get some help!

         

        Anybody wanna respond???


    • hey all!

      just joined the club.

      I modded my jca22h visually

      http://s18.postimg.org/mewy10ql5/DSCI0405.jpg

      http://s18.postimg.org/txg39nhy1/DSCI0407.jpg

      http://s18.postimg.org/hy4l2ccd5/DSCI0410.jpg

      http://s18.postimg.org/x99sp7kbd/DSCI0402.jpg

      it 's a piece of clear acrylic etched by me. I also added few UV leds

      Comment


      • Hi,

         

        I'm a new member on this forum, and I own a JC100H. I'd like to submit you an idea to add a third channel (in the way to have clean and crunch separated)

         

        To do that as simple as possible, a relay (Re1) switch a vactrol (VT 5 - VTL5C1) which allow to have an independant Master volume. Then, I thought to  duplicate a part of the channel 1, which allow to keep exactly the same features on the added channel  (except the gain pot which I replace with a trimmer which I set to determine the good value before having crunch sounds in the new channel) and choose one or an other by switching via a realy (Re2)...  But to do this, I have to put relay switch DPDT on  the grid (output 2) of the Valve n

        Comment


        •    Really digging my new JCA22H. About the only thing I'd like to change is the treble response. Its very bright.Ive tried a zillion different tubes-new and old stock and different speaker pairings. Right now I leave the presence off and the treble on 1 . Would be nice to dial down the treble output and be able to use the treble knob for varying cabs and such. Any idea's? Thinking possibly some simple "treble cut" with a pot and cap? Or perhaps a different treble cap? TIA Bob

          Comment


          • athun
            athun commented
            Editing a comment

            I'm thinking of upgrading from my JCA20H to a JCA22H, in no small part because of the effects loop. In doing some reading, some claim that the effects loop send is too hot for the input of at least some pedals. I'd mainly want to run my Boss DD-6 through it. Should there be any problems with that?


            Thanks in advance.


          • GoKart Mozart
            GoKart Mozart commented
            Editing a comment

            Rockon1,

            What type of guitar/pickups are you using? When I started playing a Tele through my JCA22H I thought that it sounded really trebly too and always left the presence on 1. I later did the Depth mod and was able to dial back in some more presence.

            If I play a humbucker eqipped guitar (right now it's a Music Man Luke III), I'm able to use the presence knob a whole lot more.

            So in summary, the depth knob helped me balance out some of the high end when using a Tele. YMMV.


        • So, total rookie question here. When someone says to swap out a component, say R9 on the 22h for example, are we talking about removing that component, or replacing/bypassing it with a jumper? I removed R9 and C10 per this thread, and now I have a lot of strange noises coming out of my amp. Also swapped out C2 with a 4.2nF cap at the same time, so I guess I can't say for sure what caused this. I'm going to put those two components back and check again, but I just want to be clear about what "swap out" means. I'm basically using my 22 to learn tube amp theory while at the same time making a good amp sound better, trying to learn little pieces of "why" as I go. However, this is an important thing I need to be clear on. Thanks in advance!

          Follow up q: Does anyone have a good recommendation for a sub-$100 output transformer upgrade for the 22h? I love this amp, but if I can squeeze just a little more volume out of it before the bottom end completely drops out it will be a whole lot more useful to me. This tranny is running hot and I think it's a weak link in this amp. Anything past 4 on the master is unusable, regardless of tubes, bias setting, or pre gain or eq settings.

          Comment


          • k
            käsebrot commented
            Editing a comment

            When someone says to swap out a component, say R9 on the 22h for example, are we talking about removing that component, or replacing/bypassing it with a jumper? I removed R9 and C10 per this thread, and now I have a lot of strange noises coming out of my amp. Also swapped out C2 with a 4.2nF cap at the same time, so I guess I can't say for sure what caused this. I'm going to put those two components back and check again, but I just want to be clear about what "swap out" means. I'm basically using my 22 to learn tube amp theory while at the same time making a good amp sound better, trying to learn little pieces of "why" as I go. However, this is an important thing I need to be clear on. Thanks in advance!

            Follow up q: Does anyone have a good recommendation for a sub-$100 output transformer upgrade for the 22h? I love this amp, but if I can squeeze just a little more volume out of it before the bottom end completely drops out it will be a whole lot more useful to me. This tranny is running hot and I think it's a weak link in this amp. Anything past 4 on the master is unusable, regardless of tubes, bias setting, or pre gain or eq settings.

             


            Swap out means just a removal.

            Look at the schematic. R9 is parallel to the 1nF at the gain pot and reduces the base a little. If you remove R9, then 1nF is in series with the former coupling cap and reacts with the gain pot as a high pass filter, tame the base in a stronger way and in another frequencies area.


            There is also no need to change the transformers. Even some people who have done this and exchanged them to Mercurys or even Onetics have admitted, that there wasn't a big noticable improvement in sound.

            I would recommend to try better tubes and to change all (!) the caps. For values up to 1nF I use good high voltage ceramic caps (just for tone stack and fizz cap Silver Micas sometimes), for values between 1nF and 22nF I use Vishay Roederstein MKT 1813, Orange Drops 225p and Sozo.


        • hi all,

          I find the lead channel of my jca100 way too bassy compared to the clean channel.

          an easy mod to perform (as no need to unmount the PCB from the chassis) is to remove or modify the value of C22. to start, i simply removed it from the circuit and the result is interesting, more bite and "liveliness"... but there is more hissss... going on with the gain > 5 (that's why C22 is there I think). I am going to try to replace it with a different value, any suggestion ??? 

           

          Comment


          • nicoch46
            nicoch46 commented
            Editing a comment

            HI

            From schematic J6/J7 are in // this mean ?   

            that is 8ohm  tap ie we must connect two 16 ohm speakers or single 8ohm ?

            or is 4ohm tap ie we must connect two 8 ohm  or single 4 ohm ????!

             

            tnx


          • nicoch46
            nicoch46 commented
            Editing a comment

            found!  the output trafo have 16 and  8 ohm tap on the back we can connect :

            single 16   on J5

            single 8    onJ6  (or J7 is the same)

            two 16    on J6 and J7

             

             


        • I haven't  checked this thread in a long time and saw the posts above mentioning footswitches. One thing I didn't like about the factory Jet City switch is that it takes up so much space on a pedalboard.I bought a few parts from Pedal Parts Plus (an enclosure, LED/bezel, DPDT switch, & a jack) and basically just copied the existing wiring from the factory switch (even reused the resistor). Works like a charm, and the LED turns blue when the overdrive channel is selected:

          Switch01

          Switch02

          Switch03

          Attached Files

          Comment


          • Long time reader first time question.

            I need help with the depth mod wire placement for my JCA 50H

            I have the original schematics and picture Edge11 posted a couple of years ago but they don't match my JCA PCB.

            PIC 1 is the original picture posted. It shows the red wire from the pot going to the speaker connection and the black wire from the pot to the PCB marked FB. (Indicated by yellow arrow)

             

            Original.jpg       

             PIC 2 is my JCA 50 PCB. There is a diode in the spot where the black wire in the original pic is placed. There is No FB slot.

            My board.jpg

            PIC 3  To solve this there is a red wire on my JCA 50 PCB running from the 4 ohm speaker jack to the FB slot on the PCB (Indicated by the yellow arrow). Can I cut the red wire in the middle and place the pot and capacitor in between them. Setting it up as pot to FB on PCB and then pot to 4 ohm speaker jack connection. Is this the right wire connection to hook up the depth mod pot and capacitor?   Thanks

            My board 1.jpg

             

            Attached Files

            Comment

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