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

[Drainbamage]

The noise isnt as bad as I was making it out to be. Surprisingly P-90 are more stable than the treble humbucker sg I have at high levels. Kinda weird. Also I did find a 1M resistor that reads 430k. Im going to replace that. Everything else reads normal.

Whats up with my power transformer? At high master Vol (6 and up) levels its noisy. Dont really know how to explane the noise but its like a hiss. Maybe its adding noise in the amplification.

[shep]

The noise isnt as bad as I was making it out to be. Surprisingly P-90 are more stable than the treble humbucker sg I have at high levels. Kinda weird. Also I did find a 1M resistor that reads 430k. Im going to replace that. Everything else reads normal.

Whats up with my power transformer? At high master Vol (6 and up) levels its noisy. Dont really know how to explane the noise but its like a hiss. Maybe its adding noise in the amplification.

does the transformer vibrate or make any noise? noise from the actual transformer and not coming out of the speaker. make sure all leads from the tranny and near the tranny are soldered well. something could have came loose from takig the board out. a hiss could be multiple things. its mostly associated with heater wiring.

by the way, anything with high gain with volume past 12 oclock is probably going to be noisy when not playing

[spadearcher]

Has anyone tried installing a Metroamp Zero-Loss FX Loop in a JCA100H? I am considering installing one so that I can use any pedals. My understanding is that this kit can be installed in pretty much any amp.

I am actually considering getting two of these, one for the Jet City and the second for a 80's Laney Pro Tube (non AOR), which is a Marshall JMP 2203 clone (has no loop)

[Drainbamage]

Shep- The transformer has what appers to be a mechanical noise, not a loose bolt or vibration ect. When I use my attenuator I really hear it. It has always been noisey even befor moding, I just didnt pin point it to the transformer. For a while I though it was the el84s.

This amp stock was not very noisey. Guess I got a good one in that matter. Later today im going back in taking out that bad resistor and adjusting the feedback.

[shep]

Shep- The transformer has what appers to be a mechanical noise, not a loose bolt or vibration ect. When I use my attenuator I really hear it. It has always been noisey even befor moding, I just didnt pin point it to the transformer. For a while I though it was the el84s.

This amp stock was not very noisey. Guess I got a good one in that matter. Later today im going back in taking out that bad resistor and adjusting the feedback.

may be a faulty transformer. not sure
although sometimes failed components on the board can cause the tranny to act up. when i built my mark preamp i had a resistor before rectification on one leg of the secondary. it caused a very loud humming noise and the tranny vibrate. put a resistor after rectification and it was fine.

[Drainbamage]

Well I got it under control. I put the negative feedback back to stock. Added a 100pf mica to ground in parralel to the 1M input resistor.
The weird voltage divider (470k 220k to ground) between the treble and master pot (only on the 20h) put those back to stock except the 220k, all I had was a 330k. Now this is the weird part. The 470k mesures half that at 230k. The 330k reads 180k. Strange. I had a 1M in there and I thought it was bad as it measured 430k. Dont know why that is.

Amps pretty quiet/stable now throughout almost all settings. The extra noise comparied from stock is the carbon films. One last thing im looking into is lowering the voltage on the power tubes. 370 is to much, way over spec at 300. To much volts is probably why the amp is brittle. Lowering the volts should make the amp more chewy!

[shep]

[quote="Drainbamage"]Well I got it under control. I put the negative feedback back to stock. Added a 100pf mica to ground in parralel to the 1M input resistor.
The weird voltage divider (470k 220k to ground) between the treble and master pot (only on the 20h) put those back to stock except the 220k, all I had was a 330k. Now this is the weird part. The 470k mesures half that at 230k. The 330k reads 180k. Strange. I had a 1M in there and I thought it was bad as it measured 430k. Dont know why that is.

Amps pretty quiet/stable now throughout almost all settings. The extra noise comparied from stock is the carbon films. One last thing im looking into is lowering the voltage on the power tubes. 370 is to much, way over spec at 300. To much volts is probably why the amp is brittle. Lowering the volts should make the amp more chewy![/quote

the resistors reading different than they should is most likely because you are measuring them while in the circuit. it is possible for the meter to read resistance through other components making a reading unlike its rating. to get an accurate reading, the resistor may have to be taken out of the circuit.

what does the 100pf in parallel to the 1meg at the input do?

i dont believe 300 is the actual max.
i see that it says that on a data sheet but it is common practice to run higher voltages. i would suggest not to change that. you could try playing with the bias to change the tone of the power amp.

[Drainbamage]

Ya I messured those resiors from the leg to leg so nothing else was in its signal path. Everything else on the board mesuerd correct. Ill see if I have the resistor I pulled and messure that to figure this out.

The 100pf to ground at input sends some very high ac frequencys to ground. My understanding is there are better ways to do this, dont know why though. Capacitor from grid to cathode or parallel a capacitor with a plate resistor. I wasnt sure the voltage (might be 100v) of the cap so that was the best place to put it as ive seen this done in other amps. I didnt do a comparison so it might not have done a whole lot. I was just trying to clean up the noise so I though I try it.

Ya lots of el84 amps run way over spec. My other el84 amps are at 300ish If I remember correct. If I can lower it with out it being to intrusive or cuting traces ill probably try it

[shep]

even though your checking resistance from leg to leg its still possible to read through other components. sometimes its not so obvious as to what else it is reading through. altering the voltage of the power amp section will also alter the voltage to the preamp section.

[käsebrot]

Lots of carbon film resistors, especially at the plates, will cause more noise. And you never should use carbon film as input resistor! Only with this, you will get way more noise!
I don't think, that lowering the nfb will be the issue.
I like the nfb resistor at values between 47k and 68k.

If the values of your resistors seem to show half of the value, maybe the dmm is out of order.
And for sure, you have to take the resistors out of the circuit to measure them properly.
But I couldn't imagine why more than 3 modern production carbon film resistors should read half the value of it's printing code. Maybe you have used not the correct values? Even if your soldering is so bad work, they won't drift all to half. They will more go up in value if you put to much heat on them.

Would be better you give the amp to a tech, who knows what he does.
I'm not feeling good about reading someone's complaints about several wrong values of resistors and plans to play a little bit of the amps internal voltages. Could be very dangerous!

[Drainbamage]

Kas I did leave the 1M input resistor alone, thats the only stock metal film I left alone.

As for the resistor drift in the treble/master vol voltage divider I did find and measure the component I pulled and it reads the value its supose to. In the circuit every thing reads half value. Every thing else on the board measures correct.

[käsebrot]

Kas I did leave the 1M input resistor alone, thats the only stock metal film I left alone.

The input resistor is 68k not 1M!
Can't imagine, how this would sound with such a big value, is there any treble left?

This resistor should avoid problems with HF. You could also lower this to 33k, then the sound will be a bit brighter, the volume of the guitar works better and you will get less noise. But use metalfilm here! If you use carbonfilm or even carbonpress, you will get a LOT more noise in hi-gain settings!

I really recommend you not to do anything with the amp again. You statet you don't know how to solder, don't know which parts are in which positions, don't know how to measure properly... really, let this go to an amp tech! There are lethal voltages in the amp!

[shep]

kas, obviously, he is talking about the 1meg to ground at the input of the first stage.

everyone had to learn at one point. even such a self proclaimed genius as yourself, käsebrot.

[Drainbamage]

Kas the 1m resistor was the input grid leak. I should have been more clear.

I aprecate your concern but you have nothinhg to wory about. For the record I do know how to measure resistance. I do know where the parts go although I admit poentiometer types confuse me. I am new to soldering on PCBs and did learn alot. For overhauling this PCB I found removing the componets from the board, sucking the solder, inserting the new componet leads in position to be soldered to be the easiest and better looking.

Im interested in your recomendation for replacing componets. Im taking a guess here... remove components, cut new component leads to size, solder and insert one componemt leg at a time while holding the compont with pliers? Thats what I did for a couple tweeks however I found that my ocd didnt think the components looked straight or apealling. For a complete overhaul I found my method to work very well.

[käsebrot]

She: Have I ever written, that I'm a genius? What's wrong with you?

Dra: Your method of soldering is ok, you could also cut of the legs when already soldered in - as I recommend to solder from the solder side (not the upper side)


I think, there's no need to waste time here anymore.
All the best for you guys.

[shep]

jca2212c sound clip after mods.

https://soundcloud.com/spenser-jarred-shepard/bomb

[KwakaZX10R]

Howdy fellow JCA'ers,

Wanted to say "hi" - I just entered my first foray into Jet City a few days ago - JCA22H and the JCA24S+ cab.

Still yet to spank the new girl out loud and with a 2 1/2yo son and 5mth old daughter, it may be a while before that can happen....plus my wife is still unaware of my purchase Thankfully the Eleven Rack lets me jam quietly to keep my wife happy!

Regarding replacing the stock preamp tubes, I know that JJ's are a pretty popular replacement around here. I was thinking Ruby's, yet there are AC5 HG, AC5 HG+, AC7 HG, AC7 HG+ and ACZ HG.....WTF??

I have also read (on this smashingly good forum) that changing V1, V2 and the PI may only be required, plus a re-bias? Or am I better replacing all, including the EL84's? Once again.....

I am not wanting to reduce gain, particularly on the crunch channel, yet would like to smooth any potential harsh treble down. As I may use the SL5 cab or my 1x12, both of which have V30's, the treble may be enough to cut the brick walls and shatter the windows if I don't tame it. My stock SL5 is almost too bright with its V30. How do the Eminence's in the 24S+ compare to V30's?

Any assistance as to the best way to go with the Ruby JJ's (or other tubes), would be awesome!

[Tortuga]

Hi - welcome to the board & the JCA club!

I got my 50H a few years ago, and immediately set about changing the tubes. After talking to Eurotubes, The Valve Queen, and The Tube Amp Doctor, I wound up going with Eurotubes' recommendation - all JJ 12ax7s with a 'matched' one for the PI. Same with power tubes. Also bought the bias probe they sell. They were very helpful with determining the right current setting for bias, and it was pretty easy to do. I've since gotten a bunch of other tubes to try out from Jay (actually reminds me, I gotta just pay him for them at this point ) that have given me other sounds to try out. Honestly, I think the best recommendation is get a solid name and a seller who will help you, and you'll do fine. There's a ton of mods you can do, too - many of which are documented in these pages.

You'll find the amp will take on a new life after tubes and bias - only then should you be worrying about eq, fizz, and other issues.

Good luck, and keep in touch!

[KwakaZX10R]

Thanks Grimespace....legend!

I will have a chat to Eurotubes and see what the recommendations are for my JCA22H and the SL5.

Thanks again!

[Tortuga]

Just re-read your first post. When the wife finds out and does you in, I call dibs on the LP!

How are you liking the eleven rack?

[Drainbamage]

I am not wanting to reduce gain, particularly on the crunch channel, yet would like to smooth any potential harsh treble down. As I may use the SL5 cab or my 1x12, both of which have V30's, the treble may be enough to cut the brick walls and shatter the windows if I don't tame it. My stock SL5 is almost too bright with its V30. How do the Eminence's in the 24S+ compare to V30's?

Any assistance as to the best way to go with the Ruby JJ's (or other tubes), would be awesome!

I think removing cap 7 is probably the only easy solution with out changing the tone of the lead channel.

[KwakaZX10R]

Hi Grimespace,

The Eleven Rack is awesome - especially after I donated to a dude named Ross (Singtall on the ER forum) after his injury and he sent me some of his rigs. I also have the expansion pack.

The standard ER presets are pretty crap - what I learnt from Singtall's rigs was the power of the parametric EQ, delay and stereo reverb. I then crafted my own para EQ, delay and reverb settings using this knowledge and it sounds so sweet now.

The ER takes pedals extremely well. I run my pedals through the front end and as I play mainly through the headphones (due to the bub in the next room), I rely on the ER for its stereo delay and stereo reverb, rather than use these pedals in the ER's loop.

Boosting some of the ER rigs with an overdrive pedal sounds epic through the headphones (Sennheiser HD280's). The ER is not really renowned for its high gain like the Axe-FX is - to get high gain, I boost it with overdrives instead and it works very well. I also have various clean patches set up with only the cab sims on....usually 4x12 V30's and various mic's / placement.

I love Gary Moore (RIP big fella!), particularly his live performances with the mad extended solo's / outro's. The Super Crunch Box stacked with the Super Blues Pro gets me outrageously close with the LP to Gary Moore's SGTB's tone from 1990's Live at Hammersmith Odeon, which is a tone I love.
[video]https://www.youtube.com/watch?v=lbJI1y0i1mk[/video]

Through my amps, the ER is still pretty awesome, although in that situation I mainly use the amps overdrive and the ER in the loop for its effects. It agrees with all my amps without an issue, even in front of the SL-5, which has no loop.

Does the ER match identically the real tube amps it simulates? No, but it is so close with many of them if setup correctly, that I really don't care. It produces awesome harmonics, particularly when boosted, and some of the para eq, stereo delay and stereo reverb plugins are straight from Pro Tools.....brilliant!

The debate will always continue regarding comparisons with the Axe-FX or similar - I am not fussed. The ER works very well for me, is very easy (particularly with the stand alone editor on my PC to avoid having to use Pro Tools), cheaper than the Axe and sounds awesome.

Re: the LP.....that will go to the grave with me (perhaps sooner rather than later, if my wife does me in for yet another purchase without permission!). The poor Tele and Ibanez are gathering dust since the LP arrived a few years ago.....you can have them instead of the LP! I just hope my wife does not sell them for what I told her I paid for them!

Cheers

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[Tortuga]

Holy Christ, dude - you seriously need to create a 'Hiya, I'm here' thread in the New Members forum and show your LP. This place will go batshit - that thing is friggin' GORGEOUS!

[KwakaZX10R]

Thanks mate - my LP is getting all shy on me.....she is very flattered by your comments!

She took a long time to find here in Oz (she sounds awesome acoustically), even longer for me to afford and now she gets spanked every night for an hour or two......then treated like royalty and religiously wiped down after use each night. The battle scars from 2 years of solid playing are now starting to show......

I originally thought I was an Ibanez man....nope, but it does sound sweet I must admit. Then I thought I was a Tele man......partly true - do love the tele. The LP though......I am smitten. She is one smokin' hot chick and sounds fuggin' awesome! During the week, I spend more time with her than my wife!!

Re: removing cap 7, as the amp is under warranty I will hold off for now. Thanks for the advice though Drainbamage, I will certainly remember this, especially if re-biasing voids the warranty anyway!

What are your thoughts on the tube sets for the JCA22H from Eurotubes??

Cheers lads

[Tortuga]

I bought a full set of JJs and bias probe from Eurotubes a few years ago. I was extremely happy with their customer service. I also contacted the Valve Queen (Laura), and she was also quite helpful - a lot of folks here buy from her. I was quite new to all this, and went with Eurotubes, I think because they offered the bias probe, and their prices were a bit better at the time.

My advice is always to contact both with the same initial question(s), and see what they say - customer service is huge with me - if they give you canned answers now, you'll probably get same (or worse) later.