What is this mod to 2204

[Brontosaur]

Is there someone able to transform this schematic onto a 2204 board layout or maybe tell me what software to use ?


Could the 2 RCs in series at V1b cathode be replaced by a 15k/1,5uF ( 13,3K with 1,45uF exactly) ?

[Groovenut]

Could the 2 RCs in series at V1b cathode be replaced by a 15k/1,5uF ( 13,3K with 1,45uF exactly) ?

That combination wont get you the exact result as the schem because of the center connection between the Rs and Cs. You can try it, but I think it would have to be the same as the schem to achieve the same results.

[rockstah]

Is there someone able to transform this schematic onto a 2204 board layout or maybe tell me what software to use ?


Could the 2 RCs in series at V1b cathode be replaced by a 15k/1,5uF ( 13,3K with 1,45uF exactly) ?

here ya go. i would wire it up as is.the turret is not needed on the second gain stage in between the cathode resistor/cap combination. just as long as the caps and resistors connect here.

Mark

[joey]

Could the 2 RCs in series at V1b cathode be replaced by a 15k/1,5uF ( 13,3K with 1,45uF exactly) ?

That combination wont get you the exact result as the schem because of the center connection between the Rs and Cs. You can try it, but I think it would have to be the same as the schem to achieve the same results.

because of the values used, the effect would be very subtle, between the two. If you wanted to increase the effect, you would want to use a smaller cap than 1uf across the 3.3k, like say .22uf. It is a form of terraced shelving then, you can do the same thing by fully bypassing the stage, and then a partial bypass in parallel

[Brontosaur]

Who could explain the effect of those RCs in series i.e. the frequency roll off from V1 cathode to ground ?

[joey]

Who could explain the effect of those RCs in series i.e. the frequency roll off from V1 cathode to ground ?

It's terraced shelving, what else do you want to know? The way it is set up in that scheme though, it is only subtly different than bypassing the whole stage.

[briango]

I just had an amp in that had pretty much exactly this mod. It didn't sound bad, but it wasn't anything that made you go holy shit either. I didn't look at the values too close, but I'm almost positive it was this or really close. There were some other HP and LP filters in a couple other spots on the one I had.

[Brontosaur]

Just got back from the bench.
Ears ringin', a big smile on my face.

This mod adds lots of gain and turns your 1 sound marshall into a rock machine with a wide array of sounds. It crunches, it wails, screams as well as it can deliver clean shimmering sounds.

For me it's a keeper !

[rockstah]

It looked pretty good and why i drew it up.
what kind of tones are getting? Guitar players?
Mark

Just got back from the bench.
Ears ringin', a big smile on my face.

This mod adds lots of gain and turns your 1 sound marshall into a rock machine with a wide array of sounds. It crunches, it wails, screams as well as it can deliver clean shimmering sounds.

For me it's a keeper !

[Icarus]

Hi Guys
Cool to see someone has tried it out & thanks to all for clearing it up as well..
I was hoping for quite a while I could get that sound back but only recently after
moving house I found that schematic sketch

Also I'm
glad someone else got to hear how this cool mod sounds it really had a Raunchy sound


Just want to say the guy that took the mods out was some guy I found when I was on tour interstate about 1500 miles away
don't think he is around anymore & i didn't have time to argue with him . (Had to get back on the road)
Nice guy but old & old school & didn't understand the whole high gain thing ,
he looked at the amp & thought oooh this is all wrong

Anyway is this mod similar to any other type of mod going around ?

The amp was modded long before i bought it so I'm wondering where the original tech that modded the amp got the ideas from ?

BTW Its a 1977 JMP 2204 I bought about 5 years ago & was in storage for years before I bought it ,
from a old Pawn type shop
I did try to find the original owner but no luck

[Icarus]

It looked pretty good and why i drew it up.
what kind of tones are getting? Guitar players?
Mark

Just got back from the bench.
Ears ringin', a big smile on my face.

This mod adds lots of gain and turns your 1 sound marshall into a rock machine with a wide array of sounds. It crunches, it wails, screams as well as it can deliver clean shimmering sounds.

For me it's a keeper !

Though the amp could sound many different ways

I remember thinking at the time Hmm I could get similar tones to Loudness (let it go ) era...
Michael Schenker early MSG tones with gain on about 4
Like i said before Accept "Balls to the Wall"
& Scorpions early 80's tones not as splatty as "loving you sunday morning"
More like "Rock you like a hurricane " "Cant live without you "
And very similar to Mathias Jab's lead tone

Very Crunchy yet clear with great gain , but not nasty or scooped sounding like modern amps

[joey]

Hi Guys
Cool to see someone has tried it out & thanks to all for clearing it up as well..
I was hoping for quite a while I could get that sound back but only recently after
moving house I found that schematic sketch

Also I'm
glad someone else got to hear how this cool mod sounds it really had a Raunchy sound


Just want to say the guy that took the mods out was some guy I found when I was on tour interstate about 1500 miles away
don't think he is around anymore & i didn't have time to argue with him . (Had to get back on the road)
Nice guy but old & old school & didn't understand the whole high gain thing ,
he looked at the amp & thought oooh this is all wrong

Anyway is this mod similar to any other type of mod going around ?

The amp was modded long before i bought it so I'm wondering where the original tech that modded the amp got the ideas from ?

BTW Its a 1977 JMP 2204 I bought about 5 years ago & was in storage for years before I bought it ,
from a old Pawn type shop
I did try to find the original owner but no luck

The short answer is that it could have been anybody, and it depends on where the amp was at the time it was modded (the change of hands many times could send it all over the place)

This mod is similar enough to alot that is around, and sometimes it is easier to tell who modded your amp by their craftsmanship, not the mods themselves...

[Brontosaur]

It looked pretty good and why i drew it up.
what kind of tones are getting? Guitar players?
Mark

Well it covers almost everyhing I love, from well defined crunch à la aussie bands (AC/DC, the Angels, Rose Tattoo) to Accept, Judas Priest and hair metal. You can also scoop the mids, put more bass an treble and play thrash /
heavy metal.
Nails perfectly the Mark Kendall from Great White sounds.

What I did realize is that my amp is no more a 1 sound machine (marshall w/crunch, w/ gain, w/more gain)
It seems to have clearer lows, more compact mids. The mod made my tone controls more efficient. I can dim gain, put more master and deliver beautiful clean tones, or in between have just enough gain to have blues wails Greeny style. Moreover, it sounds beautiful with strats, even with lots of gain.
It seems to have reached the sweet spot of those amps.



My amp is a 77 jmp modded to 2204, .047 pi coupling caps w/220k resistors, 33uF on the preamp, 16uF PI, 50 uF mains,
all caps are russian PIO, except those for the mod (1uF an 2x2.2 uF) that go to V1a which are SCR 400v polypro/metal film. I use 3w 1% metal film resistors...

Other features are a switchable Jose master (2- back to back 20V zeners) and a 250 k contour pot replacing feedback resistor, connected to the 8-om tap, 50k mid pot, 4M7 for bass and presence is a 5k/.1uF

Wow !

[rockstah]

Very cool. appreciate the feedback on it.

[Brontosaur]

Mark, your layout made it quicker, hats off !