JCA OWNERS!!! (RE)JOIN THE JET CITY LOUNGE!!!

[mesa3077boogie]

Thanks for your reply, I can see you have done quite a bit of work helping others. Im having the same issues a member Jase was having a while back where most of the diagrams and schematics to the most common mods correspond to the 50H and not the 22H. Im currently re-skimming the forums to see what he came up with as he actually raised the questions first and if he finds answers then I an find mine..

I want a clean channel. I want the satisfaction of achieving a clean channel by the work of my own two hands.

I prefer a VOX clean but realize that the clean/crunch mod in combination with the scoop mod will yield a tone more in the fender realm which is fine with me. A fender realm with also lend itself to a better marshally breakup too which is fine with me, you cant have it all..

I realize the volume will be less on the clean channel with the mods installed but isnt that what the master volume is for? Are you saying that there is no way to balance the output of both channels after the clean mods are installed?

I dont expect a lot of clean headroom out of this amp just a good chime approaching crunch at a decently loud bedroom volume is preferable.

I was hoping the clean channel could take pedals though. I do realize a bright cap makes it sound harsh with pedals but disengaging a bright cap should help it hold up better to pedals right?

I plan on installing all of the mods with indicator LED's which a whole different story that requires different parts but lets just ignore that much as I am familiar with adding the LED's to whatever info is given to me in the forum. I already have perfectly drilled holes for the toggles and perfectly drilled holes for the LED's to sit above the toggles, I just need the right layout pics and diagrams and the time to install it all.

Thanks,

mesa3077boogie

[mesa3077boogie]

I have been doing my homework, just sayin..

[Tortuga]

I think the biggest problem has been a lack of consistent schematics for the 22h. I'm definitely willing to help out, but I need to make sure we have a schematic that (at least mostly) matches up with your amp. Can you pull up the 22h diagram you have & do some comparing to your circuit? The main thing we're after is the input through V2, which is on the preamp diagram. If you can verify that all the R & C numbers match up with your board, then we have something I can use.

As far as my comments about the clean mod, yes - there's a separate master, which will let you balance out the clean vs OD channel. The problem that I found was you can't do much to balance the volume between clean and crunch, so when you flip the switch, you better be ready for it, because the sudden jump is pretty jarring. The clean takes modulation / time effects fine, it's just that (IMO) any kind of gain pedal that I've tried sounds horrible.

Adding LEDs to the switching shouldn't be too difficult, as long as you add an extra pole to each switch. So, a DPDT becomes 3PDT and SPDT becomes DPDT. The extra pole will need a voltage source and current limiter along with the LED. If you've already got that all figured out, then cool.

Would like to see the work you've done so far. Pics so much better than words with this

[mesa3077boogie]

Thanks for your response. I have schematic that was emailed directly from Jet City to myself however the schematic that shows the values of each resistor and capacitor etc. is the same one floating around the forums. I haven't personally verified every value on the schematic, but every value on the schematic that I did verify matched up with the PCB.

Yes I realize I do need a power source. On a few of my previous amps I have wired "phantom power" such as the pics below. I have been very pleased with the outcome as all of my cables are snaked into one it makes a great visual appearance.





I have all of the switches covered, as I am very blessed to have Gateway Electronics here in St. Louis which sells every resistor , capacitor and part known to man. I picked up some dual color red/white LED's for my 3 position mods I intend on installing. The 2 way LED's require yet another row of poles on the switch in order to reverse their polarity so its going to be pretty crammed in the chassis when Im done. Unfortunately I had to dremel the PCB which made me have to cut 2 traces (and replace with a corresponding wire) in order to get the LED's to center directly between a "4" and a "5" on two separate knobs, but it gonna look bitchen when its done.

Yes I promise to take and show off the pics. Once its figured out I will even post JCA22H specific DIY's for the layman.

So what do you need from me to verify how to do the clean/crunch and scoop mods?

Here are 2 side questions:
1) I see that you can apply the SLO to only the OD channel, can it be switchable all on one switch?
2) what the heck is going on in this guys blog? http://toboy-diy.blogspot.com/2013/10/j ... v-mod.html he has a bunch of 100uF caps and does his scoop mod completely different from what everyone else is..

Thanks,

[mesa3077boogie]

Im still looking for clarification on my above post however I wanted to address my questions "I see that you can apply the SLO to only the OD channel, can it be switchable all on one switch?"

I see that there is a such thing as a 6PDT. Assume that I will be replacing my 1M pots for 500K pots regardless.. That leaves 5 components that need replacing for the "SLO on OD channel only MOD". This leaves one slot to control an LED for this MOD.

Heres my question, is it wise to switch 5 components at once using a 6PDT ? I believe I can install a "SLO / normal" switch on 6PDT switch. What do you think?


Below is info I copied from an earlier post to this thread:

R9=>470k
C5 => 2.2nF
C6 => 1nF
Gain pot => 500k
R25 => 220k
C23 , C24 => 47nF



is it wise to switch 5 components at once using a 6PDT ? I believe I can install a "SLO / normal" switch on 6PDT switch. What do you think?

[Tortuga]

Not sure how you're going to wire all that, but I guess anything's possible.

Will try to get a look at schematics in the next day or so, to see what's needed

[mesa3077boogie]

Making some progress, will take more and better pics as I go..



This is two holes for phantom power and one for the resonance MOD. I though it importan to keep the spacing of the holes consistant with the spacing of the other exterior holes/jacks.



LED's for the MOD switches that will be on the front of the chassis



A preview of what one of the phantom jacks will look like



Extra tubes, why not..?



This pic looks like crap, but you can see that I already got the LED sockets installed..

[Tortuga]

Looking cool!

[clipless bumper]

Thanks Grimespace. I'm actually only after a boost in volume. Been using EQs for this function for years, but those were different loop designs. Don't really need to change the EQ-ing, so am going to try an actual clean boost. After a little reading it looks like the BLD is top of the list for me to check out.

Thanks again brother, I knew you'd be able to help!

Suhr IsoBoost is a great clean boost.

[copperheadroads]

Great thread & my first post ,glad to be here .
I have a few questions
I've recently bought a JCA22H & I starting playing with it (swap some tubes ,depth mod )
I want to do the slo mod & I've noticed that Jay's parts list calls for 1/2 watt resistors ,I have a 1/2 watt resistor kit & the stock resistors seem larger probably 1 & 2 watt resistors are stock in the amp ..I could be wrong just want to make sure .
Is there a mod to make the crunch channel more like a jcm without altering my overdrive channel ?
also If I were to upgrade some of the caps with higher quality caps of the same value ,which caps would you replace & if you have a favourite choice ?..
prefer to get everything from mouser that hunting down Sozo caps

thanks

[smcgovern13]

I've got a JCA50h. Just did the mod where you add the 100K resistor in series w/ C13 to bring back the low end at low master volume settings.

Does anyone know if you can do that heater mod that Big John shows (page 19) without cutting pcb traces? cutting those is making me apprehensive to doing that.
it doesn't seem like leaving them in tact is going to create any weird looping situations, but I haven't studied whats going on there enough to make that call at this point.

also, what is this slope mod and how is it done? seems to be popular. how does it affect the tone? etc.

I'd like to darken this amp up a bit, and maybe make the cruch channel a bit cleaner. any suggestions?
also any improvements to get rid of the fizziness would be fantastic.

is doing the SLO mod worth it? how drastically will this change the sound?

Hit me with your best suggestions!

Thanks!!!

[Tortuga]

First off, new guys! This thread is massive, as you may have noticed, but well worth the time if you're interested in working on the JCA platform and aren't seasoned 'experts' (like me). This platform affords a very good learning opportunity to the world of tube amps.

Second, make sure you understand and appreciate that working inside of these amps can kill you. 400 volts isn't something to screw with. You need to make sure you learn about filter caps and how to properly deal with them (discharging and making sure they remain discharged while working on the inside of the amp)

I can address some of the questions:
* Jay knows his shit. If he says 1/2 watt resistors, you're probably good going with his word
* Midnightlaundry is probably the most seasoned (and still fairly regular around here) as far as cap upgrades goes. Jay's posted about caps as well. See refs on page 1.
* Heater mod is covered in the thread - see refs page 1. I've done it as well. Yes, you have to cut traces, in order to remove the AC voltage from that part of the circuit board. I completely get it if you're apprehensive. Unfortunately, my experience wasn't as great as I'd hoped - if I had it to do over again, I'd weigh options such as selling - I've pretty much made the amp unsellable now.
* Slope mod is covered exhaustively in this thread. I highly recommend it - very easy to do, can be set up with a switch between different / stock values, and made the amp a hell of a lot more lively to me. See links on the ref posting on page 1
* SLO mod links are on the ref posting page 1. I believe that everyone who's done it has really been happy with the results. I'm going to do it to mine when I get a chance.

Very interested to hear about the mod done by smcgovern13. Can you diagram it out, and what was the results?

Before doing any mods, have you guys upgraded tubes and set your bias? #1 thing to do. Also, depth and slope resistor are highly recommended as well.

Good luck, ya'll. Make sure to let us know how you progress.

[smcgovern13]

Thanks for the welcome! and the info.

It looks to me like the only thing connecting the heaters to power is the JP5 to JP5 jumper, so desoldering that should allow you to make the mod and not cut traces correct? One guy said he got an amp back from soldano w/ traces in tact... maybe??? (see p19)

A schematic showing what is changing here would be very helpful. I'm having trouble following this circuit on the schematics posted (p1) anyways haha.
To me it is just looking like you're bypassing the traces in favor of wire conductor.


My plans (so far) are to do the following mods:
SLO Preamp
clean/crunch switch
bright switch (on C28)
HI-Pass fix (add 100K resistor in series w/ C13)

and anything that will fix fizziness and improve sound quality (I'm open to your suggestions && experience!)
someone posted saying that they removed C19 and that helped. this cap is in the Soldano amps.
Anyone have a technical reason as to why this would help the JCA? I might try it just to see what happens...

Thanks for the help! I'll let you know how mine turns out

[GoldstarGuitar]

Thanks for the welcome! and the info.

It looks to me like the only thing connecting the heaters to power is the JP5 to JP5 jumper, so desoldering that should allow you to make the mod and not cut traces correct? One guy said he got an amp back from soldano w/ traces in tact... maybe??? (see p19)

A schematic showing what is changing here would be very helpful. I'm having trouble following this circuit on the schematics posted (p1) anyways haha.
To me it is just looking like you're bypassing the traces in favor of wire conductor.


My plans (so far) are to do the following mods:
SLO Preamp
clean/crunch switch
bright switch (on C28)
HI-Pass fix (add 100K resistor in series w/ C13)

and anything that will fix fizziness and improve sound quality (I'm open to your suggestions && experience!)
someone posted saying that they removed C19 and that helped. this cap is in the Soldano amps.
Anyone have a technical reason as to why this would help the JCA? I might try it just to see what happens...

Thanks for the help! I'll let you know how mine turns out

just checking, have you already done a tube upgrade/re-bias? That pretty much solved my fizziness issues right off the bat. Truly, those Chinese power tubes were just awful sounding,

[smcgovern13]

Hello,

I have a octal bias probe on the way. as soon as it gets here the amp is getting a set of groove tubes. both preamp and power. hopefully that will solve the issue.

In addition to the clean/crunch switch and bright switches, i think i will add a switch to go between normal & od channels w/o the footswitch, and while im modding i may as well throw in a voice switch so I can toggle between the original and 33 K slope resistors.

that will be 4 switches added haha! so much for no swiss cheese!

I'll have to superimpose my mods onto a circuit diagram and show it off for y'all.

[Tortuga]

Absolutely, positively have to cut traces or otherwise disconnect the tube socket pins from the pcb. Otherwise, you'll just be feeding same problematic AC voltage onto the pcb.

If you don't understand or I'm not communicating this clearly enough, please don't proceed without consulting a qualified tech. This isn't an issue of warranty, it's a serious change that can't really be undone.

[smcgovern13]

Hi Grimespace,

yup I'm with it now. I may try this mod as a last resort if some of these other mods cant get it sounding how I want.
Definitely going to re-tube and bias the thing.

Thanks for the help!

[mesa3077boogie]

Hey guys so in reference to my posts above, I am in the process (slowly, wife, kids, ect) of installing 4 switchable mods on the front panel with the possibility of 2-3 more that will be out of view on the top of the chassis.

At this point I need to decide how each LED will be getting its power. As you know I am literally installling a full one spot 9V power supply inside the amp that is drawing its power from the mains wall plug internally, so that is where the LED's will get their power.

I am thinking that I am going to run one power line line that feeds all 4 front panel switches/LED's. I will tap onto that one line and give each switch its own power. So basically one line with 4 tapped spots for power. I will obviously solder the taps and cover with shrink wrap.

Here is my question: Do you think that is the best way to power the LED's or should I run 4 (or 7 if I do the other MODS) individual lines, one to each "MOD switch" ? I fear the clutter with the latter.

Thanks,

[Tortuga]

1 power line should be ok for all LEDs. Current need is real low - you'll need to limit that with resistors. I gather you know that already; just stating for anyone who may read this...

[mesa3077boogie]

Thanks for your help GRIMESPACE Im gonna stick with one wire and tap it in multiple spots.

I have 2 questions for you or others:

1) Will it matter if I go down to 20g wire for the depth MOD? Im not sure of the current guage that connects the FB and power sections (where we install the depth MOD) but looking at it appears to have a gauge that is 1.5x to 2x more strands than my 20g wire.. I have used 20g for most all my MODS in other amps with no issues and Im not quite sure it will matter for this amp and MOD seeing that the thickness of the .0047uf cap that my 20g wire will get soldered to on one of the lugs on the 1M pot has a leg/lead that a third the size of 20g wire. Anyone anyone?

2) I am thinking of the best way to word this next question. I will start here with a background piece before the question. A pedal buffer is a powered (usually by 9V) impedance matching circuit that helps you to retain clarity in long cable runs by maintaining a constant impedance by use of the buffer in your signal chain.
Here's the question: Is the "tube buffered" effects loop in the JCA22H using an actual impedance matching buffer like we think of when we use buffers on pedals? Or is "tube buffered" referring to something else?

Thanks,
mesa3077boogie

[mesa3077boogie]

Alright guys so I made some progress last night. Wow there is a lot of detailed work to get done. Nothing is hard, just time consuming. Toughest part is starting after the kids go down @ 10pm when there is no motivation left.. Such is life!

Here is the progress, nothing too fancy quite yet..

Getting everything ready for the switches to have power. I use a jar of flux and a small paint brush to assure a FAST solder. You can see my dual color switchable LED wiring diagram drawn on a piece of wood


Here is everything getting measured for the LED power taps


In process of soldering the taps


Here is everything in place as it will feed each LED on a switch




I obviously need to run a similar set up for ground.

I also still need clarification of the discrepencies in the schematics to the clean MOD (the non simple version) as it pertains to the 22H.

I also need info on my above 2 questions.

Thanks,
mesa3077boogie

[smcgovern13]

Anybody know of a mod to add reverb to this amp? I'm thinking of just finding a way to stick in a mini digital reverb permanently at the end of the FX Loop. (All other pedals i stick out front anyways - this includes analog dly & chorus)
I've done some googling and come up with nothing... let me know if any of you have seen anyone doing something like this.

Thanks!

I'll document & post if I do anything.

[mesa3077boogie]

Anybody know of a mod to add reverb to this amp? I'm thinking of just finding a way to stick in a mini digital reverb permanently at the end of the FX Loop. (All other pedals i stick out front anyways - this includes analog dly & chorus)
I've done some googling and come up with nothing... let me know if any of you have seen anyone doing something like this.

Thanks!

I'll document & post if I do anything.

I personally wouldnt want to limit myself to one type of reverb, especially a spring reverb in this specific amp. I use the TC electronic Arena reverb (which is a version of the hall of fame reverb) that comes with tone print. Each reverb setting is mind blowing. The best part is if youre trying to tame the top end due the top end not meshing with all the gain that the JCA's have, you can taylor it with the tone knob or best of all, create youre own dark reverb with the tone print editor and put that bad boy in your effects loop. That my 2 pennies.

[mesa3077boogie]

Ok Grimespace, no more need for you to research the exact caps and resistors in order to translate teh the clean and scoop mods for the JCA22H . I got it all mapped out, I just need the time and motivation to follow through with the task.

I will also detail the exact steps to do the surgery for more modders that may come along, as It has taken lots of research and the reading of a ton of posts that dont tell you all you need to know as a noob or exact the values for caps and resistors or options for the JCA22H specifically. I will do all this after Im done.

I noticed that on the HC forums you stated that you removed your 22uf cathode bypass resistor because when used in conjunction with your resonance MOD, because it produced too much bass. I seen that Edge11 said that the cahode bypass was a big part of the "scoop MOD's" sound, so Im leery to not use it.

Heres my questions:
1) do you think we could still get a significant gain boost using the cathode bypass capacitor that will yield less bass by merely using a different value cathode bypass capacitor? I realize that the cathode bypass cap boosts gain in all frequencies (as shown by Edge11's diagrams at the bottom of the page here: http://toboy-diy.blogspot.com/2013/10/jca22h-scoop-aka-srv-mod.html) so changing the value will not yield as much of a gain boost. But maybe there is another value cap that can still boost enough gain to sound good in conjunction with the scoop mod that doesnt boost as much bass?

Another suggestion would be to still use the suggested 22uf cathode bypass resistor but with the addition of using a treble peaking circuit. A treble peaking circuit can come in many flavors with the most common style being a 470K resistor in parallel with a 500pf cap ran right in line with the gain pot's "signal out" lug. I did this on a few of my amps and it sounded good. A treble peaking circuit is not a high pass filter, it merely cuts low end flub -2 to -3 DB while not effecting the rest of the signal. You really notice the change when using high gain and when palm muting. Using it on clean tones will de-mud the signal and slightly thin out the fatty bass and low mids. Using the 22uf cath bypass with a treble peaking circuit is just speculation on how to get the MODS working together well.. Any thoughts?

2) Does the 22uf cathode bypass cap need to be 400V ? I got em in 35V and 100V @home, I would hate to make a speacial trip to the store pick up a $1.50 part AGAIN..

Thanks,

mesa3077boogie

[mesa3077boogie]

Ok bros I had this made for my JCA22H and am now going to sell it before I use it. Asking $480.00 shipped. The sale is for a brand new Green Levant / Cane weave Jet City head cab with a matching 2x10" cabinet for your Jet City JCA20H, JCA20HV or JCA22H.

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Included is the head cab and the additional rear enclosure to convert the cabinet to a closed back. The speakers are not included.

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Please dont ask questions unless you are a serious buyer with cash in hand.


























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