Jca20H Mod thread and owners club.

[Fixr1984]

Can you use 1/4 watt resistors for the mods? I'm only missing one resistor for the super sucker punch and dont need anything else at the moment so I dont want to order parts if I dont have to. I would assume that they are 1/2 watt in there now so I could always just parallel (2) 1/4 watt resistors.

[Neilrocks25]

 

Originally Posted by Edge11

Nope but there is an official demo of the jca retrovalves in a jca 20h from namm I think.

So this bad boy is coming out.

More tightness you say?

Super Sucker punch mod is pretty tight like a tiger.

http://www.americanmusical.com/Item-...JCA20HWAE-LIST

And I was thinking, how many of you would be interested in a way clean mod?

 

Very interested even more so if switchable.

I am tempted to mod mine to take out as much of the gain stages as possible (switchable)

[marshallnoise]

I performed the choke and the depth mod and have to say, it wasn't difficult to do either. I did follow VH4's advice and used a 100nf/630v cap from the negative feed back trace to the lug on the pot. Super easy to do. I also used a Mojo777 filter choke for 6L6 amps for my choke. It was closer in specs to the hammond everyone was using. http://www.mojotone.com/amp-parts/tr...e-for-6L6-Amps.

As far as tone, the depth mod is a mod that has drastic consequences depending on how you twist it. I like it a lot right now, but I just want to add some girth, not the insane amount of bottom end it has dialed to the far right. So I run mine about 3 or 4. Granted, when I get to open the amp up, I don't think the depth mod will be as necessary. But it is a VERY useful knob.

The choke! Wow, talk about cleaning the amp up and keeping noise down. Very impressed. I simply clipped R3 out and replaced it with the choke. I also drilled two holes in the chassis and fed the wires through the PT grommet. Worked like a champ.

Thanks for everything in this thread guys. Much appreciated.

[Edge11]

 

Originally Posted by Neilrocks25

Very interested even more so if switchable.

I am tempted to mod mine to take out as much of the gain stages as possible (switchable)

 

If you just want to take out a gain stage you can modify dues' clean mod for that.

I'm going to post up the clean mod in a couple of minutes.

[Edge11]

 

Originally Posted by Fixr1984

Can you use 1/4 watt resistors for the mods? I'm only missing one resistor for the super sucker punch and don't need anything else at the moment so I don't want to order parts if I don't have to. I would assume that they are 1/2 watt in there now so I could always just parallel (2) 1/4 watt resistors.

 

If they give you the right value yeah. Why not try to source the part locally though?

and the complete clean mod is up.

It looks complicate but it really isn't.

If too many people find it too hard I'll simplify it.

[Fixr1984]

Question about the Super Sucker Punch mod. The mod calls for C15 as a .1uf. The schematic shows it as a 1mf. My amp has a 100mf. Should I still change it to .1uf? When you say add bypass cap on r53 do you mean to parallel it to r53? Thanks.

[Edge11]

 

Originally Posted by Fixr1984

Question about the Super Sucker Punch mod. The mod calls for C15 as a .1uf. The schematic shows it as a 1mf. My amp has a 100mf. Should I still change it to .1uf? When you say add bypass cap on r53 do you mean to parallel it to r53? Thanks.

 

you are probably looking at the wrong cap man.

And yes bypass=put cap in parallel with the resistor.

[Fixr1984]

Thanks for the bypass info. I have the combo not the head, I see that some of the components are labeled diferently. Now I just have to figure out what the correct cap number is.

On the front page the "stock" schematic, where c15 is should that be V2? The schematic shows both valves as V1

[Edge11]

 

Originally Posted by Fixr1984

Thanks for the bypass info. I have the combo not the head, I see that some of the components are labeled diferently. Now I just have to figure out what the correct cap number is.

On the front page the "stock" schematic, where c15 is should that be V2? The schematic shows both valves as V1

 

Yes that is v2.

[gretsch61]

Okay Guys 'n' Dolls!

As promised, here is a first pic of the result of cloned "JCA20H"

I have still the original JCA-Cabinet and just exchanged the front

which I have done myself. What I really like about it the "used look"

It's supposed to look like it's been used for some time.

Hope you like it! Questions are very welcome!!!

[Neilrocks25]

Edge11 I like the look of the clean mod and I am interested to try it.

I have a few questions if thats ok.

Is it fully clean or does it still get dirty, I run mine on 3.5 on the gain. If it can reach that I will be happy. But generally cleaner. As I wouldnt mind running the amp as a pedal platform.

My 2nd question, is there a lot of volume loss after the mod.

If I attempt it I will keep the tone the same but with less gain so I won't bother with the mid scoop mod.

Any pics of the mod would be awesome as I am {censored}e at following schematics.

Thanks

[Edge11]

 

Originally Posted by Neilrocks25

Edge11 I like the look of the clean mod and I am interested to try it.

I have a few questions if thats ok.

Is it fully clean or does it still get dirty, I run mine on 3.5 on the gain. If it can reach that I will be happy. But generally cleaner. As I wouldnt mind running the amp as a pedal platform.

My 2nd question, is there a lot of volume loss after the mod.

If I attempt it I will keep the tone the same but with less gain so I won't bother with the mid scoop mod.

Any pics of the mod would be awesome as I am {censored}e at following schematics.

Thanks

 

I went to mayhemfest twodays ago and I'm doing some studying at a university that isn't my own today in about an hour, I'll hit you up about your questions later today when i take a study break.

Also some of you are unable to see the image of the clean mod?

some one sent me a p.m. saying that, I however see it fine on my own browser.

[RonnieJ]

 

Originally Posted by Edge11

I went to mayhemfest twodays ago and I'm doing some studying at a university that isn't my own today in about an hour, I'll hit you up about your questions later today when i take a study break.

Also some of you are unable to see the image of the clean mod?

some one sent me a p.m. saying that, I however see it fine on my own browser.

 

Yes, that was me, it's just a little square with a ? In the middle.

I am using an iPad tho, but I have three different browsers and none show it.

Anyway, there's an Emi Swamp Thang "out for delivery" coming in and I'll post my findings using that speaker with my jca20h in the standard cab.

[Neilrocks25]

 

Originally Posted by Edge11

I went to mayhemfest twodays ago and I'm doing some studying at a university that isn't my own today in about an hour, I'll hit you up about your questions later today when i take a study break.

Also some of you are unable to see the image of the clean mod?

some one sent me a p.m. saying that, I however see it fine on my own browser.

 

No worries I am grateful for any imput. I am using my phone so I didn't see the pic, I wil check my browser.

[Si.]

Hi All.. Just received my 3rd JCA20h (stupidly sold the other 2 a while ago). I've decided to mod this one and wondered what the best first mod would be? I was going to do the depth Mod, nd there was youtube video of it somewhere but it seems to have been deleted.. does anyone still have the video somewhere?

[stilllifer]

 

Originally Posted by gretsch61

Okay Guys 'n' Dolls!

As promised, here is a first pic of the result of cloned "JCA20H"

I have still the original JCA-Cabinet and just exchanged the front

which I have done myself. What I really like about it the "used look"

It's supposed to look like it's been used for some time.

Hope you like it! Questions are very welcome!!!

 

Gretch. This is so awesome - love that Marshall plexi old school look to this! I have to do something similar to mine...

[stilllifer]

Hey gang. Came across this YouTube video of someone named Simon that did a bunch of mods to his JCA20H. Sounds really ballsy and full - massive gain that doesn't flub out and very aggressive sounding!!! Should try and contact this guy and find out what he did.

http://www.youtube.com/watch?v=N7MZU...eature=related

[Medic Matt]

Will the ja20h fit in a effects rack?

[gretsch61]

 

Originally Posted by Medic Matt

Will the ja20h fit in a effects rack?

 

If you mean 19"-Rack ?

You would have to rebuild it in a 19.0" rack wich is at least 7.0" inches in hight.

Original - DIMS: 9?Hx9?Dx19.5?W (including the ply, so you may deduct 2.0" of each DIM)

[Edge11]

 

Originally Posted by stilllifer

Hey gang. Came across this YouTube video of someone named Simon that did a bunch of mods to his JCA20H. Sounds really ballsy and full - massive gain that doesn't flub out and very aggressive sounding!!! Should try and contact this guy and find out what he did.

http://www.youtube.com/watch?v=N7MZU...eature=related

 

Go for it bro.

[Syn]

I'm going to be putting the depth mod in my JCA20h this weekend. I'm looking forward to see what kind of difference it makes!

Just a quick question, as mentioned, when I bought mine an fx loop and foot switchable clean channel had been installed. Would either of these mods, by design or done incorrectly cause a drop in gain available?

[stilllifer]

 

Originally Posted by Edge11

Go for it bro.

 

I did man - waiting for a response. Will let you know if I get one!

[gretsch61]

For all of you that really like the "Vintage Look" of a British Plexi (as I do too :-D ),

This is what my JCA20H finally looks like. Once again, this Amp has the following Mods inside,

and it truly sound very, very close to a Marshall Plexi.

Technical Mods:

- Depth Mod

- Choke Mod

- Super Sucker Punch

- Changed single Input to a full working "Lo/Hi Input"

- Changed Tubes (EL84: JJ's) ECC83's: JJ, Mullard

Design Mods:

- completly rebuild into a new Chassis, with new Marshall-like PODS, shielded wires, etc.

- Marshall In- and Outputs

- Marshall-like Front- and Back Faceplates

- 60ies Marshall-like Headshell with gold look

the whole "extreme Makeover" was @ 500,-$ incl. all the Materials

Here now some pics of the AMP:

The Pod on the rear of the Panel is the "Depth-Mod"-Pod not the selector for the

Ohm-Selector.

btw:

I am looking either for a Font for a Marshall-Emblem like this:

or someone would supply an emblem like it.

[tech21man]

 

Originally Posted by stilllifer

Hey gang. Came across this YouTube video of someone named Simon that did a bunch of mods to his JCA20H. Sounds really ballsy and full - massive gain that doesn't flub out and very aggressive sounding!!! Should try and contact this guy and find out what he did.

http://www.youtube.com/watch?v=N7MZU...eature=related

 

Sounds sick. Really really good, I didn't expect it!

[stilllifer]

 

Originally Posted by stilllifer

Hey gang. Came across this YouTube video of someone named Simon that did a bunch of mods to his JCA20H. Sounds really ballsy and full - massive gain that doesn't flub out and very aggressive sounding!!! Should try and contact this guy and find out what he did.

http://www.youtube.com/watch?v=N7MZU...eature=related

 

Update: Hey gang. I was able to get hold of the guy that did the mods on this JCA20H - his name is Ralf Simon from Germany. Credit where credit it due - I think the mods he did are amazing and his amp has tons of aggression and really solid body to it. Here is his response to me on what was changed. I have not compared his mods to any that have already been posted on this forum. Keep us posted if anyone decides to do these mods.

Hi Stillifer,

thanks for your positive comment. I am Ralf Simon from Germany and i am doing Marshall mods for years. When i came along that little JCA for a very cheap price it got my favourite preamp mods done to it and it really sounds great with it.

Anyways. The mod is not really a secret it is just a damn circuit. You may post it on the acapella jca mod forum but please give me a little credit there

Here's the changes done:

1) Hammond 156m choke

2) first filter cap 100uF

3) R45 -> 5K

4) Well matched power tubes (JJ EL84)

5) R27 -> 10K

6) R28 -> 100K

7) C26 -> 4.7nF

8) R53 -> 68K

9) C27 -> 680nF

10) R25 -> solder a 680nF across

11) VR6 -> 250K

12) R32 -> 470k

13) R33 -> 470k

14) R36 -> jumpwire

15) R44 -> solder a 1nF across

16) C15 -> 680nF

17) R43 -> 1K

You might wanna experiment with different slope resistors: 33K, 47K(ctock) or 56K too match your taste.

Furthermore the amp got a post OT lineout which sound really good when recording with impulse responses (still please do not forget a resistance at the speaker outs when doing so!!!)

Good luck!