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

[Shinigami75]

It's 820 ohm not 820k

[ashWave]

Hey y'all, I've got a weird problem with my jca100 (crunch/overdrive rocker switch version) that I've been confounded by and I'd like to get some advice before I go prodding, and at that point I'll probably make a thread about the fix. Also I'm new, so if this is bad form and I should be posting elsewhere, feel free to move this or remove it and tell me where to post :]

Anyhow, what I've been experiencing is a loud but not deafening hum, popping in and out of my signal whether or not anything is in the input jack and regardless of the speakers it's plugged into. The hum sometimes includes odd little pops or faint squeals, occurs in apparently random intervals of varying length, and is unaffected by tapping or shaking any components (yes, I tapped and refitted all the power and preamp tubes several times). The noise happens with the masters turned down so I think it's fair to assume it's somewhere in the output section though I don't have much experience yet changing caps or anything. If this sounds familiar to anyone please do share, but if not any related wisdom is much appreciated. Also with due respect please save the "give up and take it to a tech" line. I'm doing this because I want to gain experience, and I'm not going go sticking any tools or fingers anywhere without the amp being fully discharged

[Tortuga]

Just stabbing in the dark here, but maybe something in the power filtering (caps) or rectification?

Because this thread doesn't get a lot of traffic anymore, you may be best off to put this out as a standalone posting. Someone posted about a non-functioning Laney today and got quite a few responses.

I hope someone comes up with a fix for you.

[Tortuga]

Same goes for the other recent posters in this thread - I keep an eye on it, but you guys are all getting into stuff that's above my pay grade

[ashWave]

Noted, thanks much! I'll copy and paste into the general forum.

[Shinigami75]

Nice! Do you have the power section schematics?

About the gain question you have, if you don't want to change the tone too much, change R18 from 1M to 470k, or any value under the 1M really, the lower you go the more gain you drop .

You can also play with the cold clipper value (R16) , in this case is 15k. If you make it a little bit bigger you will loose some gain and make the the channel brighter. Don't go beyond 39k.[/quote]


Here's the power section

[Shinigami75]

Not sure if anyone here is aware, but looks like the Earhart coming to full mass production

First prototype (official name yet to be determined, but I can confirm it will NOT be called the 'Earhart'):



Compared to my Earhart 50:





Likely coming out in the summer, and will most likely be LESS than the HDM.

I haven't seen schematics, but I've been talking with Doug about this for a few months (had to keep my lips sealed until he released the first photo!) and I can tell you it's the Earhart in mass produced form.

If you guys want to know what it's based on, it's laid out like the Cornford MK50HII, except the Jet City version only has 1 effects loop and not 2, and this one is only EL34 and not switchable to 6L6.

Does the overdrive channel have a footswitchable option to do Crunch/Overdrive so that you have 2 channels with share EQ plus a 3rd Clean channel or it's just a proper 2-channel only amp (Clean and Overdrive)?

[rsd]

"More than likely kill off the 50H......is only EL34 and not switchable to 6L6"
So no more JCA50H with 6L6 as of this summer?

I was looking for a JCA with more jangly/clean headroom than my jca20H. Was going to mod up the 20H, but the extra channel, effects loop and mods are pushing me to just pick up a 50H with 6L6's and tweak it. (Choke and and some resistor swaps) Guess I better do that soon.


Gimes, thanks for the great thread, I've been lurking/learning here for a long time.

[rsd]

I have been waiting to post here until I can get the mods done that I have been planning for several years. I have the JCA2112RC, which is pretty much like the JCA20, except with a tube-buffered reverb unit. Of all the Jet City models, this one seems to be one of the least popular, at least for modding. I basically had to take the who combo apart to complete it, making me jealous of everyone else who has a head.

Here is the schematic:
https://drive.google.com/file/d/0B77889FOL1MnSUNTSXoxbDEzME1tQjVzaDhzYWU0UXJtelZB/view?usp=sharing

These are the mods that I completed:
156M Hammond Choke
Depth Pot
Effects loop

I will also change the tolex on the front baffle from blue to black in the next few days, add new piping in the perimeter of the cabinet and at the bottom of the front baffle.

I will not waste time on the choke and the depth mod, as these have been explained and document previously except where the choke comes into play with the B+ voltage on the effects loop.

I decided on a kit for simplicity: the Granger Kit seemed easy, and is adjustable via internal screws inside the jacks. Because I do not want to open the amp for a while once I completed the mod, this seemed like an obvious solution.
Here is the link for the Granger kit: http://grangeramp.com/ufxloop.php
I looked at a tutorial posted on the Metro Amp site (and also considered the Zero Loss effects loop, but it was more money and had an internally set level). The tutorial is the last post from dustplumb. http://forum.metroamp.com/viewtopic.php?f=7&t=32582
There are many other acceptable kits from other companies, including Iron Sounds, and also a tube buffered loop kit from London Power (a Canadian company).

Here is the upshot: the loop needs to go between the tone stack and the master volume. On both the JCA20H and the JCA2112RC, the best spot is at R14. I lifted the easiest end to work with, as I didn't take the board completely out, so I think that I ended up with the loop before R14 instead of after. If I had to do it again, I would take the resistor off the board completely, to get it out of the way, the re-solder the connection. I don't think this issue will affect the sound, but if it doesn't work, I will re-attempt it so the resistor is before the loop in the circuit.

Here is the holes drilled in the back panel of the chassis:
https://drive.google.com/file/d/0B77889FOL1MnT3JYbE13Q3hab1U/view?usp=sharing
Please ignore the extra hole. (I will have to fill it with Grimespaces favorite mod, the slope resistor switch)

Here is the loop installed in the back panel of the chassis:
https://drive.google.com/file/d/0B77889FOL1MnM19ucmVhaHV3NXM/view?usp=sharing
To the right is the depth mod.

Here is the choke where the loop draws from the B+ current:
https://drive.google.com/file/d/0B77889FOL1MncFE3N1J2NFVUX0E/view?usp=sharing
The loop is laid out extremely easy, and the directions are clear. It is a good thing that I was working on the choke anyway, as this saved me a step.

Here is the wires to the in and out of the effects loop board, where I soldered it on to the pad where I lifted R14:
https://drive.google.com/file/d/0B77889FOL1MnOTN1ZWl1dFRQVDA/view?usp=sharing
Again, I believe I placed the loop before R14. We will see how this goes....

Well it is late. I will bias the amp tomorrow if there isn't any issues and get it fired up. Hopefully I can finish the baffle and the piping as well.

Good luck with the mods. I'm interested in how it all works out for you. These are mods I'm looking to do to my JCA20h. That London Power site is mind blowing, I was trying to understand the tech articles....got very lost. His kits look pretty cool though, I'm just not sure how they'd work on my amp.

[Tortuga]

Wanna buy a JCA50H? I might consider selling mine. It's modded, but in excellent condition - the mods I've done are great, and well documented here.

[Tortuga]

And rsd!

[rsd]

Wanna buy a JCA50H? I might consider selling mine. It's modded, but in excellent condition - the mods I've done are great, and well documented here.

I might be interested. If you can PM me more details that would be great. In the meantime I'll read through the posts. Thank you.

[mbranford]

Good luck with the mods. I'm interested in how it all works out for you. These are mods I'm looking to do to my JCA20h. That London Power site is mind blowing, I was trying to understand the tech articles....got very lost. His kits look pretty cool though, I'm just not sure how they'd work on my amp.

Here's my verdict: the effects loop works great. I have been playing around with it for a few days now, and I don't have any issue with it, except the on board reverb doesn't interact well with some effects. I will continue to play around with it. I didn't go with the London Power, because I already have the tube buffered reverb, so I figured the kit from Granger would be easier.

The depth pot works as advertised, but needs to be eq'd when running overdrive pedals, and sometimes with heavy tube overdrive.

I forgot to mention that I put in 5751's in V1 and the Phase Inverted as well. Combined with the choke, I feel like the amp is much more responsive to the on-board eq and the volume of the guitar, without sacrificing too much volume. I also have a legitimate "clean" sound that is usable

While the amp fired up right away, I may have a bad connection that I will have to look for in the future, as I have some fizziness or scratchy sounds, especially as I dig in with the pick.

[Shinigami75]

Hi Folks,

How hard (and practical) is desoldering and resoldering caps and resistors for mod purposes without removing the PCB from the chassis?

[Khrille]

Hi Folks,

How hard (and practical) is desoldering and resoldering caps and resistors for mod purposes without removing the PCB from the chassis?

It's pretty easy. But it's a good idea to have a soldering suction device.

Cheers

[Shinigami75]

Hi Folks,

How hard (and practical) is desoldering and resoldering caps and resistors for mod purposes without removing the PCB from the chassis?

It's pretty easy. But it's a good idea to have a soldering suction device.

Cheers

Sure I will then! Thanks a lot

[overdrivenel34s]

Leaning towards selling my jet city 2212c. The wgs speaker upgrade helped but it still is too boxy and has this shrill high end with fizziness on overdrive channel, especially on more moderate gain settings. Converting it to a semi open back cab might help but doesn't seem worth it. I even tried a beam blocker on it which did make it less directional to an extent but no real improvement. Did played around with some preamp tube changes too...

[Dunlop]

Hello guys

Has anybody in here done choke mod on jca20h or jca22h? Does it have any (positive or negative) impact on sound? Or the only thing it does is less hiss/noises?
Is this upgrade worth of 30€?

[mbranford]

Hello guys

Has anybody in here done choke mod on jca20h or jca22h? Does it have any (positive or negative) impact on sound? Or the only thing it does is less hiss/noises?
Is this upgrade worth of 30€?

I just completed this mod, but I did it with several others at the same time. I think it is worth it, because it gives the amp smoother, creamier sound. I also added a JJ 5751 in V1 at the same time, so this may also be the tube as well. However, I like the switch so much, I will probably buy another 5751 for V2. I also prefer alternative and indie rock, so I wanted to tame the amp's gain.

The mod is not hard: you are replacing R3, the big pink resistor, with the choke. The choke has no polarity, so it can go either way. The hardest part is probably drilling the holes in the chassis. I used a step drill bit.

[Hipster Salad]

I did the choke on my 20H as well. $15 part and about 15 minutes of work. However, I ended up with using a Hammond 156L, and from what I've read since the mod I probably should have went with the 156M. Just slightly different specs on the two.

[Dunlop]

Thank you for responses

I did the choke on my 20H as well. $15 part and about 15 minutes of work. However, I ended up with using a Hammond 156L, and from what I've read since the mod I probably should have went with the 156M. Just slightly different specs on the two.

Did you noticed any change in tone?
I just dont need to waste 30€ if there is not difference

[mbranford]

Thank you for responses

I did the choke on my 20H as well. $15 part and about 15 minutes of work. However, I ended up with using a Hammond 156L, and from what I've read since the mod I probably should have went with the 156M. Just slightly different specs on the two.

Did you noticed any change in tone?
I just dont need to waste 30€ if there is not difference

There is a decimate change in tone. More headroom, more sustain, more interacitivity with guitar volume and tone controls. There is less hiss and noise, but due to the gain structure of the amp, it isn't a comple cure, but there is an improvement.

[Tortuga]

Edge11 covered the choke mod in the old HCAF JCA thread. Check my references section on page on of this thread for a link. Hopefully that information is still there.

[Tortuga]

Wanna buy a JCA50H? I might consider selling mine. It's modded, but in excellent condition - the mods I've done are great, and well documented here.

rsd - I thought you sent me a PM regarding this, but I can't find it.

After price-checking the value on my amp, I'm pretty sure it's not going to be worth enough for me to not have it any longer. I do like it, and am very interested in doing an SLO mod at some point this summer.

If you want to make an offer, let me know. I think it's a very good amp, and have done several cosmetic and functional mods that I've shared on these pages.

Thanks

[Dunlop]

I would like to do a simple line out from preamp, so I can send the signal to the another poweramp or for recording purposes.
Has anybody did that? I have 20h, so without a loop.