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

[Tortuga]

Ok, before I dig into the boards and start swapping, what's the roll favorites as far as tubes? I'm guessing new tubes benefit these tremendously?

That and bias are pretty much mandatory - at least power tubes, V1 (prob V2, too) & PI (V5). Best to get a clean start.

[thesockmonster]

Ok, before I dig into the boards and start swapping, what's the roll favorites as far as tubes? I'm guessing new tubes benefit these tremendously?

That and bias are pretty much mandatory - at least power tubes, V1 (prob V2, too) & PI (V5). Best to get a clean start.

Gotcha. An old college buddy of mine works for Carr amps, so we'll probably go through it this weekend (he's the builder/tech, I just supply the booze). Any favorites so far as tubes? Thinking a Tung Sol for V1 would help. Just dropped an old set of Mesa 12ax7's in (100HDM), and the thickness and mids increased considerably. Need to get that bite back, along with clarity.

[Meelocheck]

Can any one give me a quick explanation of what JP1 does and if changing that will have an effect? I am getting ready to make a parts run. I already have what I need to do the depth mod and I have a bunch of assorted caps & resistors. Just wondering if there is anything special I need to grab while I am out. Should I just plan on swapping out as many caps as I can? I know there are like 10 0.022uF/400V caps on the board...Should I swap the lot of those? Will changing components, even for the same value, change the tone at all? Better quality? Not worth the trouble for minimal gains?

[shep]

jp1? not sure what your refering to.

lots of people recap amps with more well known (higher qaulity) products. a lot of people swear by it. changing the material or rating of the component would make more sense to me to try different sounds, and not necessarily changing brand. i hear higher voltage or lower voltage components effect the sound as well. one thing to consider is that each component will be accurate to +- a percentage of its rated value 2%, 5%, etc. so, i would think even two of the same manufactured components plus or minus 10% (which some electrolytics are) could have a noticable (audible) difference in tone when compared to one another.

food for thought

[käsebrot]

- JP1 is a jumper in the 22H, which looks like a small carbon film resistor. It's just a "bridge", a resistor with 0 ohms.

- swapping the the .022 caps to better ones does make a huge difference, especially the couplers in the gainstages an in the phase inverter

- that depends on what you use at which place!!!

- also changing the 1u cathode bypass caps will make a huge difference, I strongly recommend to use MKT1813 there.

- Mesa 12AX7 are only rebranded JJ ECC83S, for more bite, use selected Chinese tubes like the stock ones (Shuguang 12AX7B, in selected quality go for Ruby 12AX7AC5 HG).

[shep]

i'll probably try your suggestions on the caps käs. what do you suggest for the coupling caps?

[Meelocheck]

Kas, a bridge to where? What might changing that value accomplish? Anything at all?

And thanks for the tips about the caps. May do that as long as I have the board out of the shell.

I appreciate all the help so far.

[käsebrot]

The jumper connects two traces in a case, where it's not possible to trace them directly because that would cross another trace, so it's a "bridge". You could also desolder it and use a wire, if you think, that looks better. Why do you want to set in a real resistor here?

For the caps, go for MKT1813 up to the .022 to the PI, for .1 I use Sozo Standard, also in the PI. If you want to smooth out the sound a little bit, then use a Sozo as 1st coupler and also to the crunch channel. In the tonestack, go for Cornell Dubilier DME. Cathode bypass all MKT1813. For the ceramics, use Vishay or Murata 2kV caps.

If you want something more "Metal" and/or don't like the sound of polyester and prefer polypropylene, than go for Illinois MPW, than you get more gain and more aggressive midrange. But also MKT1813 for bypassing here.

[Meelocheck]

Kas, the reason I ask about the "bridge" or jumper in this case, is because in a previous project, which was an Epiphone Valve Jr, there were two spots that simply had jumpers. Removing them would change the tone as it did, well, something. I didn't know if changing that bridge out and altering the current and/or voltage would have any impact on the sound of the amp. Again, still a noob and still learning.

[käsebrot]

Why do you call me "Kas"?
My nick here is "Käsebrot". You know what that means?

The Jet City is a whole other amp than the Epiphone Valve Jr.. The schematics are not identical (as isn't the sound). So the mods aren't, too.

I don't know, what's your goal, which sound you want to archieve when asking, if you could swap out the jumper.
I wouldn't ask, what's happen if I swap out this or that - but ask, which sound I'm looking for, and THEN decide which mods would be nice to get this.

[Tortuga]

Why do you call me "Kas"?
My nick here is "Käsebrot". You know what that means?

Looked it up: cheese bread? So, are they calling "cheese" or "bread", or is it some completely bastardized insult?

Don't go away mad because we butcher your lingo, käsebrot - we love having you and your knowledge here!

[Meelocheck]

Why do you call me "Kas"?
My nick here is "Käsebrot". You know what that means?

The Jet City is a whole other amp than the Epiphone Valve Jr.. The schematics are not identical (as isn't the sound). So the mods aren't, too.

I don't know, what's your goal, which sound you want to archieve when asking, if you could swap out the jumper.
I wouldn't ask, what's happen if I swap out this or that - but ask, which sound I'm looking for, and THEN decide which mods would be nice to get this.

Sorry, I use Kas because it is short. Some peeps just call me Meelo or Meel. And I have no clue what it means...Ok, a quick Googling reveals it to be a cheese sammich? Uhm, ok, lol...

I know the two models/amps are totally different - that is why I was asking. I got that Epi VJR breathing fire! My initial inquiry for my 22H was about how to tighten the bottom end and try to remove the fizz I get on the top end. Even with treble and presence controls turned way back, to 3 or less, it sounds fizzy to me...I can't quite explain it. I guess what I am after is the sound I hear in my head and I won't get that sound out of this amp until I can figure out which components are going to make this amp sound like the sound I hear in my head. I want darker and meaner? I dunno how to explain it. Also, I just like fiddling with stuff

[thesockmonster]

Anyone have any work done from Brian (BFG mods)? Talking to him now about having some mods done, seems like a straight up and good dude, and his mods seem to be pretty sweet.

[käsebrot]

I don't worry about my nick. And cheese-bread is right. Everyone here needs a nick and this is mine.

So firstly, to ged rid of the fizz: Replace the stock tubes in the power amp with JJ EL84 and bias the amp correctly. Should be between 18 and 22 mA, I mostly prefer 19 mA. Then you could put a JJ ECC83S on V1 position. This will also smooth out a little bit of the trebly sound, the Chinese 12AX7B in the preamp produce.

For less muddy sound and tighter bottom I would suggest to reduce the first two .022 coupling caps to .01 (or even .004 on the first).
I also like a .68 as cathode bypass at V2 better than the 1u.
Increase NFB resistor to 56k (makes the amp a little more aggressive and less wooly sounding).
For darker and more vintage sound use a 56k slope resistor and 250p treble cap in the tone-stack.
You could try to increase the fizz cap from 270p to 300p or 330p - but the higher you go, the more dull the amp will sound.


If you like an overall better sound, the only way is to change all the caps to better ones. And also the preamp tubes.

[Meelocheck]

Not sure what the bias is set at on this thing. Just can't remember what I did. I do have a set of Mesa power tubes I had laying around I put in there. I have also swapped all the preamp tubes that would make a difference I believe (V1, V2 and V5). Thanks for the tips. Been super busy lately but will get to messing with this thing eventually. Looks like I need to start gathering bits and pieces, lol...

[technomancer]

Nevermind, figured it out.

[thesockmonster]

Need to quickly kill the noise on this thing, as I've not had time to get it on the bench. Anyone tried a Decimator to kill the amp noise? If so, where? Trying to not kill tone and/or time-based effects in the loop.

[Tortuga]

Best advice seems to be elevating the preamp heaters - see prior posts on this thread (a page or two back) from Big John and Midnight Laundry. That's what I'm planning to do.

[käsebrot]

I've owned also the big HDM heads and never had problems with noise.
I don't think, that's necessary to rewind the heating.

The first step is to try good preamp tubes, especially on V1. Tung Sol 12AX7 often have noise and microfonic issues due to the design of this tube. You could buy selected and tested good ones from a trusty tube dealer. Not the regular ones, unless you are willing to buy a batch of 100 and pick out the few ones, which are really good. Don't put them into the cathode follower!!!
Otherwise go for selected JJ ECC83S (is the same as Mesa 12AX7, Engl ECC83, Grove Tubes ECC83S, TAD ECC83CZ Premium Selected, Ruby 12AX7CZ). Or seleceted Shuguang 12AX7B (is the same as Ruby 12AX7AC5HG+, Penta 12AX7, TAD 12AX7C Premium Selected, Groove Tubes 12AX7C).

Second is, to change the pots to Alphas. This also reduces noise.

Third is to try metal-oxide plate resistors (if you think, this is really necessary). But this may also affect the sound!


And - as always - all this is worthless, if you don't bias the amp properly!!!


If you really think, the amp isn't quiet enough after doing this, THEN you can mess with the heating.

[shep]

i changed the tubes in my jca2212c and käsebrot is correct about the tubes effecting the treble. it effected the tone a lot. i used jj tubes. it really cut back on the gain, but got rid of pretty much any harshness from lows to highs. only thing i didnt like as a side effect is it lost a lot of harmonic content. probably because of the lose of gain. im gonna end up switching tubes around to see what sounds best to me. as far as noise i guess it seemed a little quieter. i think it may have been from
the lose of gain through out the preamp that caused it.

picked up a jca5012 for 300 bucks. think thats a decent deal?

[käsebrot]

The 22H and 2212C both are more quiet than the 50H/100H/100HDM.

Gain on JJ Preamp Tubes varies a lot! You can get everything there, a few tube dealers also offer special selected hi-gain JJs.

[spadearcher]

Hey, be sure to add the Zoom G3 to "works in the loop." Love mine!!!

I believe that the list is for pedals that work in the loop of JCA100H, JCA50H and JCA100HDM. Those have line level loops.

Yarbicus seems to own a JCA20H instead. That amp doesn't even have a loop!

That said, I have a JCA100H and a Zoom G3, which I love. That said, the G3 sounds like ass in the loop of the JCA100H, sadly. So I guess it should be removed from that list.
My Hardwire RV-7 and TC Electronics HOF seem to work great at line level, I was planning on using the G3 for reverb and delay mostly, so I guess I will get either a Flashback or a Hardwire DL-8 and use the G3 with my other amps.

[shep]

after reading up a bit more "the tube store" recommends electro-harmonic eh-12ax7 tubes to help out with noise. here is what they say about it:

http://www.thetubestore.com/Tubes/Elect ... x-12AX7-EH

[shep]

also this article reinforces what i was saying about the jj tubes having less harmonic content. from the tube store:

From our review of this tube: "This tube sports a different plate design than found in most 12AX7's. When you look at them you can't help but think that they must be rugged and good for the musician on the road. The compact plate structure does nothing to dampen their sound or dynamic response. I find them to be well balanced. While not as harmonically rich as others I tested, they do provide high gain without the usual noise and microphonic problems you would expect. This is great sound for your dollar. If you're using a combo amp and find the Philips a little rich sounding, the JJ ECC83 / 12AX7 may be your solution."

[midnightlaundry]

I took out the stock Chinese pre's and swapped in some JJ's. I have a buttload of JJ's, and have no idea how old they are, or what state of wear they are at. I still have a GE 5751 in V1.

This amp is so aggressive that a milder tube suits it better. There's no shortage of EQ on this amp. They work good, and the shorter plates of the JJ are more stable in a combo. It sounds just fine.