Best way to add gain to a jmp 2203

[TwinACStacks]

What happens to the clean?

It goes from Pristine clean that an 800 is capable of on low gain input, to a not so clean standard kind of Marshall clean.

TWIN

 

[rudedude]

The best way is cranking it up and having a good overdrive in front of it to push your 2203.

I highly recommend the OCD by Fulltone, as someone posted in the picture.

Another very good option would be a Sparkle Drive by Voodoo Labs. This pedal is a clone of the TS808 circuit but it has an extra feature: a clean knob that allows you to have more clean mixed into the signal. This makes the overdriven tones have an excellent definition, you can really play chords at high gain settings and still get some good definition. Some other pedals would scramble the sound.

I really think this one would be perfect for you, the Clean feature in this pedal seems to be what you're looking for.

 

[SkinnyJ]

I did the "R6" mod on my '84 4104. To me, the 4.7K resistor does add gain, but makes it sound a little flubby at lower volumes. I may raise the value a hair the next time I'm poking around inside.

 

[keennay]

Killem all I think they used 2203 plus a Rat pedal? Is this right or am I thinking of a different time?

That's what I've read, but also sounds like a set of boosted/hot rodded/whatever JMP's with 6550 tubes, high treble, and low bass. An EL-34 version + Tube Screamer can easily get in Ride the Lightning territory.

 

[TwinACStacks]

I did the "R6" mod on my '84 4104. To me, the 4.7K resistor does add gain, but makes it sound a little flubby at lower volumes. I may raise the value a hair the next time I'm poking around inside.

You can play around with the Value of the NFB resistor to tighten it up a little. It's either R26 or R29 I believe.

Any time you Mod one Value usually you have to mod something else to even it out.

TWIN

 

[keennay]

Great pedal that ZW-44 is!

I bought it about a week ago and WOWIE it beats my Boss SD-1, MXR Custom Badass '78 Distortion, and modded Tube Screamer.

Just curious charveldan, which 2 overdrive pedals do you prefer in the bottom photo?

Either one of these work well, you can run the OCD at either 9 or 18 volts.

 

[nightXbrings]

Call Gibson and ask for their gain upgrade pack, it's as easy as downloading RAM to your computer.

 

[BornDead]

Rat pedal is my favorite with my JMP.

 

[Grogshla]

get out there and try some pedals for yourself.
I would suggest tubescreamer or if u just want a clean boost get a tc spark booster

 

[Joe L]

You see the 10K resistor on the cathode of V1B? Tack solder a 10K resistor in parallel with it. You see the 820 or 1K resistor on the cathode of V2A? Tack solder a .68uF @ 50V or greater across it.

You can still use the pedals listed above.

If you don't understand this, don't attempt it.

You're welcome.

..Joe L

 

[kamran]

Are you looking to replicate the tone at bedroom volume or gig/rehearsal volume? Whole different ball park.

 

[christianpaulanderson]

Either mod it for more gain or throw a silver modded tube screamer in front of it.

 

[hacksaw]

Out of the different boosts I have, ts series, sd, ds, rat and a few others, my suhr kokoboost colors less. half the time I use it as a line boost. Great pedal.

 

[Voodoo Amps]

Change the Cathode resistor on V1 to a Lower Value. I believe it's R6 should be around 10K Stock. I'd go 4.7 some even go as low as 1.2K. INTENSE GAIN.

TWIN

Glad to hear you like the 4.7K value, that’s a Mod I came up with many years ago and was posted on the Ampage. From there it was lifted and posted on Schematics Heaven. B+ voltages varied on the JCM800’s but as long as it’s not a lower voltage model this value works well.

What is the overall effect of changing the cathode resistor, as in how does changing it add gain? What are the drawbacks e.t.c

Generally speaking and without getting overly technical; changing the cathode resistor in the location mentioned will effect the gain. Lowing it from a 10K to a 4.7K will increase the gain as well as shift frequencies, in this case you will add a little more lower mids and low end.

I did the "R6" mod on my '84 4104. To me, the 4.7K resistor does add gain, but makes it sound a little flubby at lower volumes. I may raise the value a hair the next time I'm poking around inside.

You may have lower B+ voltage, have you taken voltage readings on all the plates?

Any time you Mod one Value usually you have to mod something else to even it out.

This is true 98% of the time

You see the 10K resistor on the cathode of V1B? Tack solder a 10K resistor in parallel with it. You see the 820 or 1K resistor on the cathode of V2A? Tack solder a .68uF @ 50V or greater across it.

You can still use the pedals listed above.

If you don't understand this, don't attempt it.

You're welcome.

..Joe L

For those not in the know; Soldering a 10K across a 10K gives you 5K, which is very close in value to 4.7K. I would caution soldering a component across/in parallel to another component that is mounted on the pcb unless one is very experienced with soldering. IE: Often times the solder connection under the board may be compromised and audio may cut in/out. I only mention this as we've repaired many amps due to this.

Soldering a .68uF across V2A’s cathode sounds cool but it will effect the amp’s ability clean up as well when rolling down the guitar’s volume knob. If you don’t use cleans then this will not matter


Have a great day & I hope it helps in some small way!
Trace

 

[charveldan]

Great pedal that ZW-44 is!

I bought it about a week ago and WOWIE it beats my Boss SD-1, MXR Custom Badass '78 Distortion, and modded Tube Screamer.

Just curious charveldan, which 2 overdrive pedals do you prefer in the bottom photo?

They're both great but if only one it'd be the Zakk ...

 

[Joe L]

Glad to hear you like the 4.7K value, that’s a Mod I came up with many years ago and was posted on the Ampage. From there it was lifted and posted on Schematics Heaven. B+ voltages varied on the JCM800’s but as long as it’s not a lower voltage model this value works well.

Trace! Long time no see in the forums. And yep, I'm an Ampage old timer. I was the guy building the first SLO clones.

Not to hijack the thread but how to you think Joe's OEI plexi transformers have held up against the latest offerings?

..Joe L

 

[damienbeale]

Glad to hear you like the 4.7K value, that’s a Mod I came up with many years ago and was posted on the Ampage. From there it was lifted and posted on Schematics Heaven. B+ voltages varied on the JCM800’s but as long as it’s not a lower voltage model this value works well.

You came up with?

Pardon me, but this is the most obvious place in the world to look for more gain in a master MkII circuit.

Either the plate, or the cathode. Since this side of the tube is the rather cold biased side, and not run so hard as V1a, it couldn't be MORE obvious if it tried. Especially since lowering the cathode resistor puts it closer to some more traditional values.


I'm pretty much 100% certain, that most decent techs worth their salt as far back as 1976 would have come up with the same conclusion.
I'll be damned if this wasn't a common mod long before the internet took off.

 

[Joe L]

I'm pretty much 100% certain, that most decent techs worth their salt as far back as 1976 would have come up with the same conclusion. I'll be damned if this wasn't a common mod long before the internet took off.

And that statement says it all. Trace, being a decent tech as you say, came up with the same conclusion early in his days working on amps. He was generous enough to post the information on Ampage and it was copied and pasted without credit on the Schematics Heaven site. There were a lot of pro techs on Ampage back then both active and lurking and no one jumped in to say "oh, that old mod".

And that is what it was like before the internet. Techs were tight lipped about their mods and even if they weren't, there was no public forum to spread the word.

..Joe L

 

[ravines]

The old 2203's have a heap of gain (& volume!) on tap, I use a ZVEX super hard on into my 2204 great single dial gain/volume boost with a slight colour! Really recommend that pedal.

 

[Voodoo Amps]

Trace! Long time no see in the forums. And yep, I'm an Ampage old timer. I was the guy building the first SLO clones.

Not to hijack the thread but how to you think Joe's OEI plexi transformers have held up against the latest offerings?

..Joe L

Hi Joe! I have 1 or 2 OEI's I recently found when we moved to a larger facility. Out of all the plexi OT's we just recently I still prefer the one we had Mercury clone. There's just something really cool about it that I like. Fee free to email me and we can catch up (so this thread isn't hijacked--lol).


Thanks!
Trace