Brit 800 2204 vs 2203 thoughts

aens said:
Thanks a lot Leon, I must’ve missed that. What a pain to buy Marshall amps from this era since you can’t be entirely sure what’s inside the chassis…


Not in front of any of my Fractals for a few weeks, but this will most probably do the trick.
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Thats why gut shots are important.
 
Budda said:
Thats why gut shots are important.
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Exactly! And even with those you might have to consult a Marshall expert. Same thing with some pedals that have gone through multiple revisions (like 80’s-early 90’s Dunlop Crybaby as an example).
 
You still need to know your way around the amps. PCB was the same across "lead" and some "bass" models, master volume and non master volume, and 50W and 100W amps from mid 70s JMP through to mid 80s JCM 800. Mustard caps dissappearing was the main difference in the late 70s. UK and Canada models came with EL34 tubes, US models with 6550s. There are some minor circuit differences between the 2. I think the idea was to get them sounding more similar with the different power tubes. Evidently spare EL34 availability was poor in the US at the time.

I had a '78 JMP 2203 that was half mustards and half poly film, or whatever the first of the replacement caps were. I still have a 50W bass head (model 1986) from '77 or '78, that was reconfigured to be a 2204 not long after I bought it, and is now rebuilt as a non-master volume 50 watt in a loosely "plexi" spec. Really different sounding amp configs with no changes at all to any major components.

Gut shots across either 50W or 100W are really similar. You kind of know what you are getting once you know which model is which, but as @York Audio found, it can be really hard to find one that hasn't been modified or otherwise messed with. I have been responsible for some of this over the years... ;)

Liam
 
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Since the FM3 didn't get the 100W JCM800 yet, has anyone found a proper method to tone match the bigger brother with the 2204?
Possibly via advanced parameters etc.
My reference amp has way less gain than the 2204, broader midrange, less 'pissed off' if that makes sense.
 
SJG said:
My reference amp has way less gain than the 2204, broader midrange, less 'pissed off' if that makes sense.
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The 2204 had several internal variants, some had normal HT voltage (~465v) but only one 10k preamp B+ dropper, these were lower gain and high headroom but not quite like the Horizontal Input revision.

The infamous 2204 schematic by Mark Huss is of his high HT and singe 10k dropper '83 variant.
https://mhuss.com/MyJCM/

If I may suggest, it would be cool to have the single 10k dropper variation of 2204 because there were plenty of them in the wild and the current 2204 and 2203 models sound damn near identical.
 
James Freeman said:
The 2204 had several internal variants, some had normal HT voltage (~465v) but only one 10k preamp B+ dropper, these were lower gain and high headroom but not quite like the Horizontal Input revision.

The infamous 2204 schematic by Mark Huss is of his high HT and singe 10k dropper '83 variant.
https://mhuss.com/MyJCM/

If I may suggest, it would be cool to have the single 10k dropper variation of 2204 because there were plenty of them in the wild and the current 2204 and 2203 models sound damn near identical.
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That was quite informative, thanks for sharing. Do you think there’s a way to get closer to the single 10k preamp version by tweaking some parameters in the current 2203 ?
 
FractalAudio said:
The 2204 models have a 10K dropping resistor between the B+ and PI. The 2203 models have 20K. The 2203 has about 17% more preamp gain than the 2204 as a result.
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Big thanks for the clarification and for paying attention to all these details. Thought the gain was higher in the 2203 model after the amp and speaker interaction update, but this explains it. Think I’ve missed a few updates since the 2203 model dropped so it’s hard to keep track. But who cares, keep the updates coming 🙏🏻
 
FractalAudio said:
The 2204 models have a 10K dropping resistor between the B+ and PI. The 2203 models have 20K. The 2203 has about 17% more preamp gain than the 2204 as a result.
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This piqued my interest sufficiently to dig out my old amp books and have a look at some of the schematics. Interestingly the 2203 seems to have a 20K dropping resistor for the PI (in fact 2 x 10k in series in most) in all the schematics, except for the last of them, revision dated December 7th, 1988, which has a single 10K. Gets me wondering if that was one of the reasons the "horizontal input" 2203 was less well loved.

I've been trying to figure out when the 2204 went from separate preamp tube inputs to "cascaded" inputs, which the 2203 had from the earliest schematics in 1976. It seems to have been somewhere between the original JMP 2204 schematic in 1976 (possibly similar in '78, but dates are hard to read), and the earliest JCM800 schematic I have, dated April 24th 1981. Gets me wondering whether the circuit changed when the JMPs became JCM800s, or whether that change happened before.

Would I be pushing the boat out too far to request High and Low input models for the original JMP 2204 as well as the JCM800 2204? 🤣

Liam
 
LiamH said:
I've been trying to figure out when the 2204 went from separate preamp tube inputs to "cascaded" inputs, which the 2203 had from the earliest schematics in 1976. It seems to have been somewhere between the original JMP 2204 schematic in 1976 (possibly similar in '78, but dates are hard to read), and the earliest JCM800 schematic I have, dated April 24th 1981. Gets me wondering whether the circuit changed when the JMPs became JCM800s, or whether that change happened before.
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FWIW, I used to own what I believe was an unmodified JMP 2204 from '78 that had cascaded gain stages. I've been curious as to when they changed from the parallel stages, too. Not sure this helps much to narrow it down and I no longer have the amp to verify.
 
LiamH said:
Gets me wondering if that was one of the reasons the "horizontal input" 2203 was less well loved.
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Horizontal Input revision had only one 10k dropper between Screens and PI even on the 2203 and another missing 10k between PI and V2, resulting in a completely different sound.

The video bellow is a must watch, including the best A/B comparison of Horzontal/Vertical revisions on youtube.

 
James Freeman said:
Horizontal Input revision had only one 10k dropper between Screens and PI even on the 2203 and another missing 10k between PI and V2, resulting in a completely different sound.

The video below is a must watch, including the best A/B comparison of Horizontal/Vertical revisions on youtube.
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That has turned out to be an awesome rabbit hole, thanks so much @James Freeman! I had a look at a few of those videos, including the "Jake E Lee" mods. I actually have a couple of 6-position rotary switches on the back of my original and best 1980 JMP 2203, so I can substitute a cathode resistor on one gain stage, and a cathode bypass cap on another to similar effect.

Really funny to discover that the main issue with the horizontal input amps was the increased preamp plate voltages due to the filtering changes, rather than the amps actually being inherently disastrous. Back in the day we just stayed away from them, but vertical input JMP MV amps were relatively much more available and affordable back then! I wish I'd figured that one out - it's really obvious from all the old schematics that I had back then, and still have now.
Churchhill said:
FWIW, I used to own what I believe was an unmodified JMP 2204 from '78 that had cascaded gain stages. I've been curious as to when they changed from the parallel stages, too. Not sure this helps much to narrow it down and I no longer have the amp to verify.
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The funniest thing about the rabbit hole @James Freeman sent me down, was I got to thinking "I may as well just buy a '77 or '78 JMP 2204 so I can check if they are cascaded or not, maybe see if @Churchhill's memory serves him (or her) well." (Other personal pronouns available, I'm only "woke" within limits of my age and upbringing.)

More than when, I also wondered why the 2203 and 2204 preamps were so different. I guess the 2203 would have been a much higher price with 2 more valves and sockets, an extra filter cap, and a lot more iron and copper in the transformers. They weigh a lot more, noticeably so by the third flight of a fire escape leading to the back stage entrance! So maybe the completely "smash the back doors in" gain and bite added to the value of the higher priced amp. I'm sort of willing to find out, so I had a quick look on Reverb and eBay to see what's available to buy...

Mary mother of god! Not many available, and $3000 for a horizontal input 2204? o_O Worse than that, I also found a "big box" 50 watt JMP model no. 1987 from 1975 (if you know, you know), with toggle switches rather than rockers. No gut shots, and they either know not to post, or they don't. You'd have to buy it to find out. I'm going to try my hardest not to.

So I've learnt a bit, I'm GAS'ing for more Marshalls than I have since the late 90s, and I'm more aware than ever that Fractal ownership is still saving me a small fortune, at least temporarily!

Liam
 
@LiamH Definitely "him" - I like to sleep in way too much to be "woke" :eek:

Yeah, prices on these have gotten insane since the pandemic. I've still got a '75 big box 1987 that someone modded with lamp cord to the point I was afraid to plug it in. Bought it for parts years ago and still need to rebuild it.

My JMP 2204 was very similar to my '80 JMP 2203, but I ended up with an '83 JCM800 2204 that is much more thick and gainy than the JMP version was. Not sure why, but I've really been on a Marshall kick lately, too. Beautiful thing about Fractal is it's really scratching that itch!

The one I've always been curious about is the JMP 2150, almost the same thing as the Park 1210, from around '78 (I think). Apparently, it's got the parallel inputs like a 1959/1987, then an additional gain stage like a 2203, and a master volume. I've only seen one once, didn't play through it, but on paper at least, it looks like an interesting amp. Been awhile since I looked at the schematic, but I seem to remember thinking the Park (head) seemed a little more interesting than the version released as a Marshall (combo) although I don't remember why I thought that.
 
Churchhill said:
The one I've always been curious about is the JMP 2150, almost the same thing as the Park 1210, from around '78 (I think). Apparently, it's got the parallel inputs like a 1959/1987, then an additional gain stage like a 2203, and a master volume. I've only seen one once, didn't play through it, but on paper at least, it looks like an interesting amp. Been awhile since I looked at the schematic, but I seem to remember thinking the Park (head) seemed a little more interesting than the version released as a Marshall (combo) although I don't remember why I thought that.
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I had a JMP2150 for a while and have a Park Rock Head 1210 coming this week. 2150 was fun, sort of its own thing but definitely some similarities to a 70’s Super Lead and 2203. Pretty gainy, I basically always kept the bass at 0 and used the normal channel for low end as it would have a kind of twangy low end thump that was different. Took pedals pretty well too.
 
I'd be curious to hear what you think of the 1210 and how it compares to the updated 2203/2204 and the available Plexis. I've heard (can't confirm) that the 1210 was the basis for the Wizard Rock Standard, too. In any case, congrats on your new acquisition!!
 
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