Simple mods to a 2203 - Metallica RTL

peterc52

peterc52

Well-known member
I would love to have just a tad more tight gain coming from my JMP 2203 '83. Maybe a slightly different EQ.

I aim for RTL sound. Can anyone point me in the direction? :D
 
Changing V1b from 10k to 6.8k or 4.7k will get you a little more gain without changing the overall tone much if any..
 
I'd say any good Marshall amp with the overdrive of your choice and add an EQ pedal of your choice to tighten things up as well with EMG pickup they used should get that tone.
 
I believe rtl was a tube screamer in front of a stock marshall jmp.... they had just had the jose amps stolen and were trying to find a replacement, I just read about this somewhere. The sm7b mic on the cab was a pretty big part of the sound imo to !

As far as simple mods, you could throw a .68 uf cap over v2a cathode for a little more bite , you could change the first coupling cap to a smaller value to tighten up the amp , piggy back a 10k resistor and .47 cap on v1a cathode 10k ... you could do a fixed resonance mod to like Friedman... so many options...
 
Lowering the resistance value on the second cathode aka cold clipper by putting a resistor across the stock 10k, and/or putting a .68 uF cap across it, as people have mentioned above, are simple gain-increasing mods I've done. There's a thread in this same sub-forum a couple months ago that has some ideas, links to how-to vids, and a schematic that is a certain well-known amp builder's high-gain take on this sort of mod.

https://www.rig-talk.com/forum/thre...ome-mods-looking-for-some-suggestions.215495/
If you want to get close to metal levels of gain but still have tightness in the low end, IMO you would want to do what that well-known builder did: add 3.3k and .68 uF paralleled across the 10k (gives significantly more gain) and also add the 220k from the gain pot to ground (reduces boomy lows and tightens the low end).
 
^ The gain pot mod you mention sounds like it’s changing the impedance? It’s looks like it’s turning the 1meg pot into 180k?
 
Last edited:
psychodave said:
^ The gain pot mod you mention sounds like it’s changing the impedance? It’s looks like it’s turning the 1meg pot into 180k?
Click to expand...
Yes, It changes the way the first stage is loaded.
It's not exactly like changing the value of the pot because of the voltage divider formed by the 470k and the 220k preceding the pot. It also leaves intact the relationship between the 1n bright cap and the 1M pot values.
But it certainly affects freq response and signal voltage passed to second stage.
 
I’m trying to buy back a 2203 I built many years ago. And will mod it. It will be easier than on the PCB in the JMP. Thanks guys!
 
I just modded my 2204 to JEL ch2 specs. Sounds really good. Just a tad bit more gain. Also it has a bit more fatness to it. I need to try it with a boost but it was an easy mod to do. Took like 5-10 components and is easily reversible
 
dawnofdreamx97 said:
I believe rtl was a tube screamer in front of a stock marshall jmp.... they had just had the jose amps stolen and were trying to find a replacement, I just read about this somewhere. The sm7b mic on the cab was a pretty big part of the sound imo to !

As far as simple mods, you could throw a .68 uf cap over v2a cathode for a little more bite , you could change the first coupling cap to a smaller value to tighten up the amp , piggy back a 10k resistor and .47 cap on v1a cathode 10k ... you could do a fixed resonance mod to like Friedman... so many options...
Click to expand...
These are all great suggestions, the first coupling cap can do a lot for you. If it's a 22n, try a 2.2n or 4.7n. Also, what tap are you using for NFB? NFB tap can change a lot and you could also do a variable NFB with a pot
 
I've played a lot with this and one thing people don't also consider is the volume factor. The 2203/04 changes with volume. Some of your mods might become " too much" once the amp is cooking with the master in what I consider to be the sweet spot at 6 or 7. On one of my clones, the tone is incredible with a few mods and at volume. I actually run the preamp a bit lower and it just cooks. With a boost it will do those tones no problem. EMG pups will just get you there sooner. This one adds a nice touch to my ear but the key is not turning preamp up too high. Some good ideas in this thread though:

2. You can also increase the plate resistors values to add more gain from 100k up to 150k or 220k (insane). I don't like this mod as much, it gets buzzy.

Instead of 100k, I have upped mine to 120k. Not much more but just a bit more oomph. .68 uf cap over v2a cathode is also a go to.

you could change the first coupling cap to a smaller value to tighten up the amp

I have this on a switch.

piggy back a 10k resistor and .47 cap on v1a cathode 10k

This was too much for me (or for my amp anyway, it is always dependent on the sum of all your parts and your amp) , I've gone back to just 10k. 5k or 4.7k got a bit mush at higher gain.

Oh, and 47k vs 100k on NFR, a bit more JMP'ish for your 2204 and keeps things tight. Gain reduction but you've already made that up elsewhere.

Ultimately you have to decide if this will be a boosted amp or you are going to try to make the amp to do the work. I think small mods and a little nudge from a boost and volume still yield the best results. Again, everything changes so much at volume that the differences between boosts even become a wash.. hence why SD-1 and TS anythings have stayed in vogue. Low volume playing has made our ears picky because you hear more differences between the boosts. I think anyway.
 
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