Mod Ideas for JMP 2203 Build

[ibzprestige]

I built a jmp 2203 kit last year from parts from valvestorm, while it sounds great, I just really haven’t played it much so trying to get ideas for mods to do to it for fun. I currently have 2 Jose mods and a JEL modded 2204, so I have those basis covered. What am I missing?

 

[DanTravis62]

Variable negative feedback.

It's literally the most important mod you can do on that circuit IMO

 

[FourT6and2]

Yes, variable NFB is cool.

Variable slope resistor

"Feel" control (found on some Fortins and Camerons), but really only useable with a Jose mod

Depth + thump

Add another tube for 4 or 5 gain stages

Plate-fed tone stack for a 4th stage

 

[GlideOn]

I would love to see one voiced for KT66.

Maybe a bit higher PI caps to .047s or .056s and decrease the PI entry cap to .0068 or .0047 to compensate.

Huge, chunky low mids instead of the usual high mid emphasis.

 

[ibzprestige]

Yes, variable NFB is cool.

Variable slope resistor

"Feel" control (found on some Fortins and Camerons), but really only useable with a Jose mod

Depth + thump

Add another tube for 4 or 5 gain stages

Plate-fed tone stack for a 4th stage

Do you happen to have any general schematic or layouts for any of these? A lot of stuff I see out there I never know if it’s correct or not, just want to make sure I’m doing things right, haha.

 

[SpiderWars]

Plate-fed tone stack for a 4th stage

OP, since you have two Jose's and a JEL already an Aldrich mod might be cool. Since it's a Valvestorm build you could do anything.

 

[FourT6and2]

Do you happen to have any general schematic or layouts for any of these? A lot of stuff I see out there I never know if it’s correct or not, just want to make sure I’m doing things right, haha.

Variable NFB is just a pot. Let's pretend your NFB resistor is 100K. Lower it to 27K (just an example) and then use a 100K linear pot wired as a rheostat with that 27K in series. Now your NFB is variable from 27K to 127K. Adjust your resistor and pot values to taste.

Same with with variable slope. Lower slope resistor value to 27K and wire a 25K linear pot in series. Now your tone stack center freq. resistor is variable from 27K to 52K. Most common hard values are 33K, 39K, 47K, 56K. Adjust your resistor and pot values to taste.

Depth control is a 1MA pot with 4700pF cap wired up to your NFB circuit. Other values to try are 2200pF and 3300pF. Thump control is something else.

All of these things, including a plate-fed stack circuit are available online if you spend some time searching.

 

[ibzprestige]

Variable NFB is just a pot. Let's pretend your NFB resistor is 100K. Lower it to 27K (just an example) and then use a 100K linear pot wired as a rheostat with that 27K in series. Now your NFB is variable from 27K to 127K. Adjust your resistor and pot values to taste.

Same with with variable slope. Lower slope resistor value to 27K and wire a 25K linear pot in series. Now your tone stack center freq. resistor is variable from 27K to 52K. Most common hard values are 33K, 39K, 47K, 56K. Adjust your resistor and pot values to taste.

Depth control is a 1MA pot with 4700pF cap wired up to your NFB circuit. Other values to try are 2200pF and 3300pF. Thump control is something else.

All of these things, including a plate-fed stack circuit are available online if you spend some time searching.

Awesome, thank you! Adding an extra tube or going to a plate fed tone stack is where I get a bit mixed up since theres so much out there it gets overwhelming for a hobbyist like me with not a ton of free time, haha.

 

[ibzprestige]

OP, since you have two Jose's and a JEL already an Aldrich mod might be cool. Since it's a Valvestorm build you could do anything.

Good idea, so the Aldrich is a plate fed tone stack?

 

[jchrisf]

I like how the new Modded 800 sounds. I'd want to do those.

 

[WarHed]

Good idea, so the Aldrich is a plate fed tone stack?

Yes. Completely different circuit to an 800 (i.e. not a mod), but a cool sounding and aggressive circuit

 

[iff]

"Feel" control (found on some Fortins and Camerons), but really only useable with a Jose mod

Why is that?

 

[FourT6and2]

Why is that?

Best with dual gain control and the rest of what goes into a diode clipping 800 circuit.

 

[glpg80]

@FourT6and2 I always thought thump and resonance were interchangeable terms but you’re making it sound as though they’re separate? I don’t need technical details but what makes them different?

 

[FourT6and2]

@FourT6and2 I always thought thump and resonance were interchangeable terms but you’re making it sound as though they’re separate? I don’t need technical details but what makes them different?

Resonance/depth is what most refer to a 1M Log pot with a cap, usually 2200pF - 4700pF. A "thump" or "punch" control, as you might find in some hot-rodded amps, uses a very small cap across the depth control, with some combination of resistors and caps on a switch in parallel with that cap and pot. And I'm pretty sure you saw the recent thread where I posted like 5 different schematics of that circuit. At the end of the day, it's still a "depth" control. But the thump/punch switch gives you the ability to fine-tune what frequencies the depth control accentuates.

One such example:

47K NFB/8ohm tap
1MA pot with 470pF cap across it
On a switch, and in parallel with the pot, you then have a 47K resistor in series with a 4700pF cap

Of course, cap and resistor values to taste.

 

[jasonP]

I think a good amp to (copy) go with the ones you listed would be the Friedman BE - JJ or SS circuit, with variable depth and NFB

 

[glpg80]

Resonance/depth is what most refer to a 1M Log pot with a cap, usually 2200pF - 4700pF. A "thump" or "punch" control, as you might find in some hot-rodded amps, uses a very small cap across the depth control, with some combination of resistors and caps on a switch in parallel with that cap and pot. And I'm pretty sure you saw the recent thread where I posted like 5 different schematics of that circuit. At the end of the day, it's still a "depth" control. But the thump/punch switch gives you the ability to fine-tune what frequencies the depth control accentuates.

One such example:

47K NFB/8ohm tap
1MA pot with 470pF cap across it
On a switch, and in parallel with the pot, you then have a 47K resistor in series with a 4700pF cap

Of course, cap and resistor values to taste.

I didn’t realize giving a frequency control was really desired - you’re describing just common tuning of any resonant center frequency which to me once you’ve got it dialed in you just set it and forget it.

 

[Chubbs]

Outside of what others have mentioned, I would highly recommend trying the SIR39 mod. It’s another gainstage but still sounds like a Marshall and pretty easy. Jason has a good how to video.
And if you don’t mind hacking up your chassis, I’d try putting a bunch of stuff on switches. Also recommend a decade box. Kinda spendy but saves you a ton of time experimenting.

 

[ibzprestige]

Outside of what others have mentioned, I would highly recommend trying the SIR39 mod. It’s another gainstage but still sounds like a Marshall and pretty easy. Jason has a good how to video.
And if you don’t mind hacking up your chassis, I’d try putting a bunch of stuff on switches. Also recommend a decade box. Kinda spendy but saves you a ton of time experimenting.

I couldn’t find Jason’s video on it. Wonder if it got deleted

 

[FourT6and2]

I didn’t realize giving a frequency control was really desired - you’re describing just common tuning of any resonant center frequency which to me once you’ve got it dialed in you just set it and forget it.

Tons of builders including Bogner, Cameron, Fortin, Larry, Wizard, Monomyth, and Friedman have done some version over the last 40 years. Yes, it's common. Whether you want to implement it or not is up to you.