panhead
Well-known member
A transformer is gonna go like a tube aka like a light bulb. Not much warning
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Racerxrated
Well-known member
Better get that Superlead checked out. Mine flattens my last 2203, which was the best 2203 I’d ever owned.
A healthy 100 NMV Marshall should completely obliterate a great 2203 in volume; and it won’t be close.
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Mikeyboyeee
Well-known member
Not saying they're not louder or as loud, but at similar volume, something is rattling in the room when playing the jcm 800 boosted VS the 2 Superleads. Same cabinet. Same dB.
All into a PS100 btw.
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Racerxrated
Well-known member
Try yours stock; no PS. That’s where I’m coming from. When both are boosted, the 72 buried my old 2203, which had healthy GE 6550s and new caps, and believe it or not it outdid my old Coli at 180w. All I could hear of the Coli was the low end. Lol
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Mikeyboyeee
Well-known member
Believe me, I know they're loud. These happen to have MVs, but I've had other Plexi NVM as well and without attenuation, they're brutally loud.
I've run everything I've had without the PS100.
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Racerxrated
Well-known member
I recorded a little clip with mine, double boosted just to show how saturated it can get. My phone was set on top of a cab I wasn't even using; and it was walking itself to the side of the cab. Lol. The sound pressure was punishing.
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turboblues
Active member
I'm sure it is, these days. ?
Bardagh
Well-known member
Thanks for the replies guys. I don’t know how much it would contribute to the overall issue but I think something in the circuit between the high and low inputs might be messed up since I’m getting a lot of buzz when I plug into the high input. In any case I ordered new jacks so when I get my tubes and the jacks in I can eliminate those variables.
However I took a look in the amp and while it seems stock (maybe a couple caps and a screen resistor replaced at some point) the impedance selector looks a little weird to me, not that I totally understand it in the first place.
If I’m looking at it right and the color coding of the schematics I found are correct, it looks like the NFB is on the 4ohm tap, which I didn’t think would be the case, and a 2.2k resistor has been wired between the 8ohm tap and the lug that goes to the hot connection of the speaker jacks. I haven’t seen anything to indicate that resistor should be there and I don’t even know what effect it would be having in that spot.
Any ideas?
However I took a look in the amp and while it seems stock (maybe a couple caps and a screen resistor replaced at some point) the impedance selector looks a little weird to me, not that I totally understand it in the first place.
If I’m looking at it right and the color coding of the schematics I found are correct, it looks like the NFB is on the 4ohm tap, which I didn’t think would be the case, and a 2.2k resistor has been wired between the 8ohm tap and the lug that goes to the hot connection of the speaker jacks. I haven’t seen anything to indicate that resistor should be there and I don’t even know what effect it would be having in that spot.
Any ideas?
glpg80
Well-known member
That 2.2k resistor off the speaker Jack is your problem - remove it. It shouldn’t be there.
There are ways to protect the OT with 8 ohm resistors on certain style jacks so that if you forget to plug a cabinet in, the OT doesn’t become an expensive fuse. However that’s not what is going on here and not the correct way to implement such protection.
That resistor is not stock and does not belong - I’d remove it. It’s causing an impedance mismatch for any setting that isn’t the 8 ohm setting, essentially shorting two secondary taps together through the 2.2K resistor. As expected it sounded like an impedance mismatch and that resistor proves what I heard.
There are ways to protect the OT with 8 ohm resistors on certain style jacks so that if you forget to plug a cabinet in, the OT doesn’t become an expensive fuse. However that’s not what is going on here and not the correct way to implement such protection.
That resistor is not stock and does not belong - I’d remove it. It’s causing an impedance mismatch for any setting that isn’t the 8 ohm setting, essentially shorting two secondary taps together through the 2.2K resistor. As expected it sounded like an impedance mismatch and that resistor proves what I heard.
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Bardagh
Well-known member
Thanks, I’ll pull it later today and see what happens. What do you think about the NFB being on the 4ohm tap? I’ve seen a wide range of opinions on whether the 2204 should or did come with the NFB on the 4 or 8ohm tap. To me part of the JCM 800 sound is that its a bit more raw, so I wouldn’t want to increase NFB too much, but I wonder if a little taming might not help with some of the extremes of bass flub and squirrely top end.
glpg80
Well-known member
Honestly I’d leave it on the 4 ohm tap and fix the issue at hand first, a rogue resistor. Nothing wrong with the 4 ohm tap IMO. Pull the resistor and make some new clips, I bet you’ll be surprised.
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Bardagh
Well-known member
Sure enough, it's sounding better. Went through the greenback cab and it isn't farting out anymore. This was yet again with presence and eq all at noon, preamp around 6-7 and MV around 3. Starts out with volume rolled back in middle position on my Les Paul with Marshallheads - cleans up nice! Hit a slight boost towards the end. This same set up sounded like the speakers were going to blow the other day, so weird.
Next I want to see if I can reduce the buzz I'm getting through the high input and I may look at doing the "Jake E Lee" mod.
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tonesfoyobones
Well-known member
Oh hell yeah bud! So glad it wasn't anything major. Sounds so much better!
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Racerxrated
Well-known member
The NFB mod (moving the purple wire to the different taps) is the easiest “try it and see” mod you can do. Try the 8 ohm (tighter) then the 16 (tightest) and figure out which one sounds best. 8 ohm I think is typically stock.
glpg80
Well-known member
I wouldn’t change that for anything - sounds just like a booster Marshall should!
Glad I could help ?
Glad I could help ?
lowmantotempole
Well-known member
OMG dude! I had no idea! I’m so sorry. I’m the second owner of that amp and I don’t know anything about wiring amps that’s for sure so I didn’t put it there.
Bardagh
Well-known member
It’s all good, if I was upset about it or something I’d have dropped you a line directly. I’m not surprised to see stuff having been done in an old amp. It’s actually almost totally unmolested - but I’ll probably change that.
LPMojoGL
Well-known member
The JMP 2203 I had was brutal loud when cranked.
The JCM 4-holer took my breath away and made me sterile.
Sounds like OP got it figured out! That's great. You never know what's up in these old Marshalls. I've seen all kinds of stuff, glue, caps on tube sockets to ground, funky stuff.
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