Guitar Gear Forum

Here's a lit of changes and the parts to change the JCA 22H, 50H and 100H to the SLO preamp. These are links to each of the individual parts. I'll try and do an XL spreadsheet at some point to really condense this stuff. Anyway, here goes!

Change R41 (1m) to 470k: 470K
Change C27 (.001) to 2n2: 2n2
Change C21 (470p) to 1n: 1n
Put C21 on toggle for Warren Haynes mod:
Change R19 (100k) to 220k: 220K
Change C10 and C11 (22n) to 47n: 47n
Change R42 (1m) to 470k: 470K
Change C28 (250p) to 470p: 470p
Put C28 on toggle for Bright mode:
Perform Edge11 clean mod or do simple clean if desired. I'll post up the details from the JCA thread from HCAF a bit later.

This might make it easier. Just highlight and copy the list below. Then paste it to the BOM or Import tool on the mouser website, and it will generate a list for you. Just go through the checkout procedure and you get your parts. I'm going to resourse the caps that seem to be going obsolete. I'll also put together a list of some other readily available capacitor choices for those of you who would like some other options. Enjoy!

71-CCF60-475K-E3
75-715P600V0.0022
75-715P1600V0.001
71-CCF60-221K-E3
75-715P600V0.047
75-715P600V0.047
71-CCF60-475K-E3
594-D471K25X5FL63L6R

Jay wrote:This might make it easier. Just highlight and copy the list below. Then paste it to the BOM or Import tool on the mouser website, and it will generate a list for you. Just go through the checkout procedure and you get your parts. I'm going to resourse the caps that seem to be going obsolete. I'll also put together a list of some other readily available capacitor choices for those of you who would like some other options. Enjoy!

71-CCF60-475K-E3
75-715P600V0.0022
75-715P1600V0.001
71-CCF60-221K-E3
75-715P600V0.047
75-715P600V0.047
71-CCF60-475K-E3
594-D471K25X5FL63L6R

This is most impressive. Parts ordered and on the way!

Most of these parts show EOL.

racerevlon wrote:Most of these parts show EOL.

That's why in the OP, I said I would go back and resourse the caps that are going obsolete. You can still get them while supplies last. I'll get back on it in a bit.

SLO mod + Depth mod gut shot pics

Jay wrote:Here's a lit of changes and the parts to change the JCA 22H, 50H and 100H to the SLO preamp. These are links to each of the individual parts. I'll try and do an XL spreadsheet at some point to really condense this stuff. Anyway, here goes!


Change C21 (470p) to 1n: 1n

This one right here, I copied from the list when I ordered, and I was sent a cap with the same capacitance and tolerance, but for 1600volts, and not 600volts. OK to use for C21? I have since bought another cap at Radio Shack just in case, and that's what is in C21 as of now.

sahlomonic wrote:

Jay wrote:Here's a lit of changes and the parts to change the JCA 22H, 50H and 100H to the SLO preamp. These are links to each of the individual parts. I'll try and do an XL spreadsheet at some point to really condense this stuff. Anyway, here goes!


Change C21 (470p) to 1n: 1n

This one right here, I copied from the list when I ordered, and I was sent a cap with the same capacitance and tolerance, but for 1600volts, and not 600volts. OK to use for C21? I have since bought another cap at Radio Shack just in case, and that's what is in C21 as of now.

From what I know, there isn't a problem going with a higher voltage rating. Same goes for wattage ratings on resistors. Aiken says that you might even get better clarity for going higher wattage on resistors.

Randall Aiken wrote:Contact noise
Contact noise is dependent on both average DC current and resistor material/size. The most significant contributor to noise in guitar amplifiers is the use of low-wattage carbon composition resistors. Since the noise is proportional to resistor size, the use of 2W carbon comp resistors will improve the performance over that of 1/2W resistors. Studies have shown a factor of 3 difference between a 1/2W and a 2W carbon comp resistor operating at the same conditions.

Here are the pots you will need as well -

Two 500k PC mount 16mm (mini) audio/log:

http://www.newoldsounds.com/index.php?m ... s_id=11305



Exact drop in replacement, and actually the shafts are better quality IMO because they aren't split or prone to breaking off.

Here's a clip of the completed mod:

[video]http://www.youtube.com/watch?v=C980z_sCGTM&feature=share[/video]

dude, that sounds killer!!!

That's nothing compared to stage volume. I gigged with it last night, and it is a friggin'MONSTER. I love that it still has the same basic tone, but it is so much more open and aggressive. I think it sounds its best with the OD gain set fairly low on the dial, like at 3. Still enough gain for hard rock/metal.

Are the board locations the same on all the amps?

Also what would be the changes if I only wanted the SLO mod on the Overdrive channel and a super clean channel on the Crunch channel.

Bump!

Dark Helmet wrote:Also what would be the changes if I only wanted the SLO mod on the Overdrive channel and a super clean channel on the Crunch channel.

super clean with just 2 EL84s? highly unlikely unless you're just playing at home, not with a drummer, anyways you can do the 39k resistor to ground and srv mod, that should make it much cleaner.

For the SLO OD looking at the schematic you need to change this:

R9=>470k
C5 => 2,2 nano Farads
C6 => 1 nano Farad
Gain pot => 500k
R25 => 220k
C23 , C24 => 47 nano Farads


The schematic for the jc22h:

sahlomonic wrote:Here are the pots you will need as well -

Two 500k PC mount 16mm (mini) audio/log:

http://www.newoldsounds.com/index.php?m ... s_id=11305

What's the advantage of changing the stock pots for these? Do they make that much of a difference that makes it worth the hassle of pulling the stock ones out?

Thanks!

and I thank all of you for sharing all of this! I bought a 22H and love it! Reading this forum has given me the bug to mod amps!

Axisman5150 wrote:What's the advantage of changing the stock pots for these? Do they make that much of a difference that makes it worth the hassle of pulling the stock ones out?

Thanks!

I think the reduced resistance reduces the overall gain range, since you replace the gain pot.

I could be wrong, but I did the mod and I replaced the pot and the gain was significantly reduced.

Which is a good thing since the JCA has a fuckton of unusable gain after 10:00 on the gain knob.

This looks really interesting. Where to find a JCA 50 on the cheap. Gotta try this mod.

maynardo wrote:

Dark Helmet wrote:Also what would be the changes if I only wanted the SLO mod on the Overdrive channel and a super clean channel on the Crunch channel.

super clean with just 2 EL84s? highly unlikely unless you're just playing at home, not with a drummer, anyways you can do the 39k resistor to ground and srv mod, that should make it much cleaner.

For the SLO OD looking at the schematic you need to change this:

R9=>470k
C5 => 2,2 nano Farads
C6 => 1 nano Farad
Gain pot => 500k
R25 => 220k
C23 , C24 => 47 nano Farads


The schematic for the jc22h:

Are these changes correct? Sorry, I don't want to insult you I just don't want to make any mistakes thats all!! LOL

Also do you have the output side schematic with the component values on it?

A good friend that contibutes to my blog recently bought a JCA22H and has been doing a few mods.

He did a breakdown of some on the blog which some may find intersting. There are a few more to come. SRV mod and such

www.backline.tk

Toe-Knee wrote:A good friend that contibutes to my blog recently bought a JCA22H and has been doing a few mods.

He did a breakdown of some on the blog which some may find intersting. There are a few more to come. SRV mod and such

http://www.backline.tk

Link didn't work. Tried http://toboy-diy.blogspot.com/

Odd it should work. Thanks for posting up the additional link!

The main reason for using a smaller gain pot is to reduce noise which in a high gain amp with lots of stages is a good idea. It also changes the loading of the stage which has some subtle effects and implications for tone shaping. As far as operation goes its just a potential divider and its the ratio that is important, not the explicit values.