Guitar Gear Forum

Dunlop wrote:Hello guys, I will be a new (hopefully proud) owner of JC amps (jca22h)

For first I wanted to ask, is there any way how to install depth mod without drilling a new hole into chasis?
My amp will be new with 3years warranty, and it is chinese amps so I think that warranty may be good way how to fix it if something went wrong :-)

Thanks

You could use one of the speaker jack holes for the depth pot. Does the 22 have chassis mounted spk jacks like the 50?
Of course you lose a speaker output. probably voids the warraty unless you undo the mod before the warranty work.

Thank you guys for quick answers, but 22h (unlike 20h) has speaker jacks mounted on pcb I think. But it looks like only possible way

maynardo wrote:

ironman28 wrote:No disrespect to Mr. Friedman and his peeps but there is nothing infringing here that they can complain about. The first schematic is from the HCA forum and is EDGE11's take on the fmbe mod. It is almost identical to the second schematic as far as the component values but no saturation switch. The other two pics are of the posters personal amp.
I would be interested to see your pictures of the work done by friedman compared to the picture I posted above. I dont know if that is representative of his work. It looks more like a DIY job than a professional mod.

That picture IS from friedman's work, I have another one where the guy went with sozos everywhere . If you register in sloclone forums you can see many more pics from marshall's he or his people modded and they're as messy or more than that one you posted

Best regards

$500?

No i think he charges 250 to do it on a jc, 500 was with the amp included i believe.

Best regards

maynardo: my PM does not work, maybe because I am new or something like that. Can you please send these schematics/pictures/whatever into my mail? Thank you

Dunlop wrote:Thank you guys for quick answers, but 22h (unlike 20h) has speaker jacks mounted on pcb I think. But it looks like only possible way

There is always more than one way!

The fixed depth mod is good if you can live with the one setting. You could use a P-P pot to turn it off/on.
You can reassign another control to the depth pot, but you lose that control, for example like the presence.
You can replace one pot with a concentric one and have two knobs on one shaft.

Dunlop wrote:maynardo: my PM does not work, maybe because I am new or something like that. Can you please send these schematics/pictures/whatever into my mail? Thank you
kurdt.kombajn (at) gmail.com

I just sent it, but again the 2nd schematic posted by ironman28 is correct

ironman28: now I am a bit embarrassed, I totally forgot about these stacked pots. It looks like the winner. Thanks
maynardo: thank you, appreciate it

@Dunlop

No worries glad to help in your tone endeavours

Posted some schematic errors in the doc thread
Anybody that has a JCA50 can you check the values of R35 and R36 in your amp?
My amp does not match the schematic I have 220k in R35 and a 470k in R36

Thanks

Hiya, ironman28 - I just put a reply in the documentation thread. Thanks for your help with this.

By the way, if I didn't say so already, welcome to the club. Your apparent knowledge will certainly contribute to the wealth of resources involved in this group!

If you don't mind me asking, where'd you come from?

you should write an email to jet city asking for a current service schematic mentioning the voltage divider error you founded.

BTW the schematic from the jca22 has some errors as well , mjtripper has corrected one... I dont know if there is a doc thread for that amp tho

You are welcome!

I was on HC until 2005/2006. I lurk and post at diystompboxes and freestompboxes lately
My blog is here; http://ironman28.wordpress.com/

ironman28 wrote:Posted some schematic errors in the doc thread
Anybody that has a JCA50 can you check the values of R35 and R36 in your amp?
My amp does not match the schematic I have 220k in R35 and a 470k in R36

Thanks

I didn't check the 50 I just modded, so I wonder if it's just a line change. Does yours have the two rocker switches or the metal toggles? I'm wondering if they were both a simultaneous change.

The two divider circuits are both outlined in a few different amp books. They both offer similar performance, with the lower values giving less resistor noise.

Mine has the rocker switches
The attenuation ratio is the same for 220k/470k compared to 470K/1M but I think the gain is lower in the first but the HF rolloff is lower with the second. If you look at the pic posted above those resistors appear to have been changed after the assembly line. The solder joints are clearly different from the rest. Not really a problem just interesting as to why they were changed and when.

That is odd. I wonder why they did it like that. JCA is pretty good about answering emails. Shoot them a quick one and see what they say?

Doug @JCA says they did make a change to those values after launch.

I wonder how much does the overall tone actually changes with the different v. divider , load & output impedance in that stage stage.

Found this reference to R35-36
http://www.captainbob.de/modifications.html (use google to translate)

He lists them as part of the SLO mod

I have looked at the 100h/100hdm photos on the forum but the resolution is not high enough to read the resistor values.
I am thinking JC changed the values for R35-36 on the 100 watt models also at some point. If you want to get as close as possible to SLO specs then these resistors should be checked and/or replaced as part of the SLO mod.

Jay wrote:Really? Have you taken them apart? Wonder what the difference is.

Sorry about the delay. I think they're wired in reverse, or the power for the LED is on a different pole. I think if you plug the 22 Switch into a 50/100 it doesn't work, and if you plug a 50/100 into the 22 it works, but no LED. I'll have to experiment and verify. Bottom line, if you own both, LABEL THEM!!

Does any one have the SLO mod for the 22H? I think Jay a forum member posted the values and the board locations but I believe that they are different for the 22H.

Just posted a bias mod for the JCA50 in the DIY/mods section

Dark Helmet wrote:Does any one have the SLO mod for the 22H? I think Jay a forum member posted the values and the board locations but I believe that they are different for the 22H.

Check the website I listed above. He has a list of parts for the 22h
http://www.captainbob.de/publicuse/JCA5 ... ersion.pdf

Check the website I listed above. He has a list of parts for the 22h
http://www.captainbob.de/publicuse/JCA5 ... ersion.pdf

I have the parts, at what Jay listed but the board locations are not the same for the 50H and 22H.

The 22H is pretty responsive to tube changes. I have not modded this one yet, but I can tell you that I do NOT like the JJ ECC83s in it. The 803s is good in V5, but that's it. It DOES like a good selection of a few choice 60s tube I have hanging around. 60s Mullard I have and RCA grey plates sound FANTASTIC in V1. Just used some Penta Chinese tubes in V2-V4 and some other oddball tubes in the PI and the tones are so much better to me. I've really been gelling more with the crunch channel with a boost than just the OD channel.