Hi guys,
I recently built a Marshall JCM800 2204 clone, but with a few minor changes, however, I'm getting some weird problems.
I used this layout:
http://site.triodestore.com/JCM8002204Stock.pdf
I removed the 'Lo' Input and connected the 0.022uf capacitor to the resistor/capacitor input on the 'Volume' pot.
I also removed the presence control, and the 100k resistor connecting the OT secondary to ground.
The weird problems I'm getting are:
When I turn the 'Volume' up past 1/4 I get really bad crackling/fuzzyness. But If I keep the volume below this level and turn the 'Master' up its fine.
Also, when I adjust the TMB controls, it doesn't seem to do much, other than at about half way, but not as desired. Could this be because I've connected all the ground wires together, then one final wire to a grounding bar?
I recently built a Marshall JCM800 2204 clone, but with a few minor changes, however, I'm getting some weird problems.
I used this layout:
http://site.triodestore.com/JCM8002204Stock.pdf
I removed the 'Lo' Input and connected the 0.022uf capacitor to the resistor/capacitor input on the 'Volume' pot.
I also removed the presence control, and the 100k resistor connecting the OT secondary to ground.
The weird problems I'm getting are:
When I turn the 'Volume' up past 1/4 I get really bad crackling/fuzzyness. But If I keep the volume below this level and turn the 'Master' up its fine.
Also, when I adjust the TMB controls, it doesn't seem to do much, other than at about half way, but not as desired. Could this be because I've connected all the ground wires together, then one final wire to a grounding bar?
I'm not following you on #1. Can you sketch out a schematic of how you actually wired your amp?
#2... This is the negative feedback circuit of your amp; you can't remove it and tie the 100K resistor to ground. The amp will no longer sound like a Marshall 2204. It may not even work as it should. The 100K resistor injects output signal back into the phase inverter, it isn't supposed to be attached to ground on either end.
What I would do is wire the amp exactly like the drawing you have, make sure the amp works and sounds right, then start doing mods to it if you want to change the sound.
The whole point of the 2203 & 2204 was so with the "HI" input the guitar's signal went through an additional gain stage vs. the "LOW" input.
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I get it, he wired the unwanted low jack circuit as if the jack were empty, in other words he replaced the cutout contacts with a wire.
I suspect, and especially with the removal of the feedback, that as you turn up the volume, your amp is breaking into oscillation. It is oscillating at high freqs above audio, what I would call RF. It still passes audio, but now is noisy and weak. This would be apparent on a scope. Or we could knock together a basic RF detector for a meter.
I agree, you really should restore teh negative feedback circuit.
I suspect, and especially with the removal of the feedback, that as you turn up the volume, your amp is breaking into oscillation. It is oscillating at high freqs above audio, what I would call RF. It still passes audio, but now is noisy and weak. This would be apparent on a scope. Or we could knock together a basic RF detector for a meter.
I agree, you really should restore teh negative feedback circuit.
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