JCM 900/2100 mods

B

Buffalo Computer

New member
Does anybody see a problem with installing a switch for the clipping diode mod? Would shielded cable need to be used?

Also, anybody know of any other switchable mods that would make a noticeable tone change?
 
Do you want to be able to footswitch the diodes on/off or similar? I only mention because you can effectively remove the diodes from the circuit by just turning the gain sensitivity all the way down. Unless you have something else in mind of course...
 
TotallyRadGuitars said:
Do you want to be able to footswitch the diodes on/off or similar? I only mention because you can effectively remove the diodes from the circuit by just turning the gain sensitivity all the way down. Unless you have something else in mind of course..
Click to expand...


TotallyRadGuitars said:
.The mod that I'm talking about would not be the same as turning down the gain all the way. Different diodes I'm assuming? Why would anybody suggest to mod by clipping the diodes if that's attainable by zeroing on the gain?
Click to expand...
 
TotallyRadGuitars said:
Do you want to be able to footswitch the diodes on/off or similar? I only mention because you can effectively remove the diodes from the circuit by just turning the gain sensitivity all the way down. Unless you have something else in mind of course...
Click to expand...
I also wasn't thinking foot switch, I was thinking about throwing a hole and putting an additional switch on the front of the head.
 
TotallyRadGuitars said:
Do you want to be able to footswitch the diodes on/off or similar? I only mention because you can effectively remove the diodes from the circuit by just turning the gain sensitivity all the way down. Unless you have something else in mind of course...
Click to expand...
The mods I am looking for would be along the lines of switching on and off the feedback loop, anything else switchable that would make a noticeable difference in tone that will not be able to be done by the usual controls.
 
Gotcha, I wasn’t sure what your goal was from the first post.

So yeah, you could do a switch to change the type of diodes. Maybe a 3-way, stock/off/LED’s or something. There’s some funky stuff going on around V1B so be careful you don’t make any big sweeping changes without testing or you might end up with a weird/bad sound. I’m not an expert but I know there’s something about phasing in there that kills some ultra high frequency hiss that probably should be left intact.

Power amp negative feedback could be a switch or another knob to fine tune, or add a resonance control too. That’d have a strong effect (if desired) on the low end.

An easy one that would have a strong effect is to either change or do a 3-way switch for different values of the EQ slope resistor. That’s R20 on the schematic, stock it is 33k same as most classic Marshalls.

You may have already seen this but there are a few subtle mods listed by NewReligion on the Marshall forum. I haven’t done them myself but feedback is very positive:
https://www.marshallforum.com/threads/free-easy-mods-for-jcm-900-2500-2100.99502/
I’m basically in kindergarten compared to that guy’s level of knowledge

Rock on
 
You must log in or register to reply here.
Back
Top