LP Freak
Well-known member
I'm definately going to try this mod out. 
codyjarrett
New member
LP Freak":1l0rsauv said:I'm definately going to try this mod out.
This schematic is the same circuit that is in my JMP 2204 and in the clips I posted.
By codyjarrett at 2012-07-03
Heres a pix on the board.
By codyjarrett at 2012-06-23
LP Freak
Well-known member
Thanks for sharing. 
codyjarrett
New member
LP Freak":pq4qxnex said:Thanks for sharing.
Not a problem
I love this mod because you don't have to drill holes and it's plug & play.
Basically a sleeper.
grooveHT
Well-known member
Great tone and playing Cody! Some awesome clips, thanks for posting.
codyjarrett
New member
grooveHT":gaiblgpy said:
Thank you for the feedback.
Shawn Lutz
New member
Nice Marshall hard rock tone...
I have a stock 83 JCM800 2203 with 6550's that I love the simplicity, SD1 in front and it screams.
I have a stock 83 JCM800 2203 with 6550's that I love the simplicity, SD1 in front and it screams.
codyjarrett
New member
Shawn Lutz":1sw71w8f said:
Thank you.
Yeah I really like the tone of a stock 2203 and sd-1.
I've used this setup many times.
Kapo_Polenton
Well-known member
What I did to the 2204:
1. Replaced the V1A cathode resistor (10k stock) with a 4.7k and bypassed it with a .1uF FILM RADIAL cap.
2. Replaced the V1B cathode resistor (2.7k stock) with a 820r and changed the stock .68uF to a .47uF bypass cap.
3. Bypassed the V2A cathode resistor(820r) with a .68uF cap.
4. Tone stack lift ( removed the ground wire from the 25K L middle pot.)
5. Replaced the 33k tone stack slope resistor with a 47k.
6. Replaced the 100k NFB resistor with a 47k.
7. Replaced the stock .1uF on the presence to a .68uF.
8. Lowered the stock filtering (50uf+50uf) to 32uf+32uf preamp (16uf+16uf screen/PI) I left the mains at 50uf+50uf.
The tone stack lift gives the amp more gain, the middle bass ect. controls will lose some FX but very easy to dial in this way.
The .68uF (SoZo) on the presence affects the mids & highs.
The .1uF (stock) only affects the highs.
The 47k NFB resistor makes the amp sound '67-'68 plexi.
It's a little tricky working on a PCB board.
The thing is you don't have to disconect all the wires from the PCB board.
Just prop it up with something so that you can get underneath the broad with the solder gun and try not to burn the wires.
Make sure you always discharge the amp before working it.
Cheer's Cody
Awesome... thanks for that. I have a few of those changes already but like the tone stack lift idea! That PCB is a total bitch. I think i am going to do this on my gutted Laney instead as it makes swaps MUCH easier.
codyjarrett
New member
Kapo_Polenton":22epyv0z said:What I did to the 2204:
1. Replaced the V1A cathode resistor (10k stock) with a 4.7k and bypassed it with a .1uF FILM RADIAL cap.
2. Replaced the V1B cathode resistor (2.7k stock) with a 820r and changed the stock .68uF to a .47uF bypass cap.
3. Bypassed the V2A cathode resistor(820r) with a .68uF cap.
4. Tone stack lift ( removed the ground wire from the 25K L middle pot.)
5. Replaced the 33k tone stack slope resistor with a 47k.
6. Replaced the 100k NFB resistor with a 47k.
7. Replaced the stock .1uF on the presence to a .68uF.
8. Lowered the stock filtering (50uf+50uf) to 32uf+32uf preamp (16uf+16uf screen/PI) I left the mains at 50uf+50uf.
The tone stack lift gives the amp more gain, the middle bass ect. controls will lose some FX but very easy to dial in this way.
The .68uF (SoZo) on the presence affects the mids & highs.
The .1uF (stock) only affects the highs.
The 47k NFB resistor makes the amp sound '67-'68 plexi.
It's a little tricky working on a PCB board.
The thing is you don't have to disconect all the wires from the PCB board.
Just prop it up with something so that you can get underneath the broad with the solder gun and try not to burn the wires.
Make sure you always discharge the amp before working it.
Cheer's Cody
Awesome... thanks for that. I have a few of those changes already but like the tone stack lift idea! That PCB is a total bitch. I think i am going to do this on my gutted Laney instead as it makes swaps MUCH easier.
Not sure how this circuit will sound in a Laney, only because it doesn't have Dagnalls for iron like my JMP's.
The PCB is a bitch to work on but if you just take your time when working on them you can get great results.