Marshall Volume Question

[Pole With Soul]

I have just recently acquired a JCM 800 head, 50 watts, 4 input (1987 style, i.e. no master volume). This amp ROARS on a volume setting of 1! Is there a different volume pot I can have installed that will make this a more useable range (taper)? Would a master volume installation be more effective?
Thanks

[Swarty]

A smaller value bright cap is probably what you need. It will either be on the volume pot or on the circuit board depending on when the amp was produced.

[Pole With Soul]

Thanks! The amp was made in 1989. Any idea before I pull out the chassis where the bright cap would be?

[samtheman]

Thanks! The amp was made in 1989. Any idea before I pull out the chassis where the bright cap would be?

Maybe the one across the 1ch volume pot ?

/sam

[Swarty]

It is a small ceramic disc on the circuit board straddling the trace that goes to the volume pot for channel 1. Lots of guys just snip these out.

[John Phillips]

I would fit a MV. Changing the value of the bright cap is a good idea (I would use 500pF - removing it entirely makes it too dull IMO), but won't make that much difference to the volume taper. These amps just get very loud, very quickly..

I would fit a Post-PI MV, which you can put in the hole for the DI Level control (if the amp has one, I can't remember whether JCM800 1987s do - the other models do) - if not, remove the second speaker jack. If you use either the Crossline MV with a no-load pot, or the Ken Fischer type MV, the amp will be back to exact stock when the control is up full so you lose nothing and gain some more useful control. The Crossline MV doesn't even require you to work on the PCB, although that's not really an issue with these amps since it's easy to remove.

[Pole With Soul]

I would fit a MV. Changing the value of the bright cap is a good idea (I would use 500pF - removing it entirely makes it too dull IMO), but won't make that much difference to the volume taper. These amps just get very loud, very quickly..

I would fit a Post-PI MV, which you can put in the hole for the DI Level control (if the amp has one, I can't remember whether JCM800 1987s do - the other models do) - if not, remove the second speaker jack. If you use either the Crossline MV with a no-load pot, or the Ken Fischer type MV, the amp will be back to exact stock when the control is up full so you lose nothing and gain some more useful control. The Crossline MV doesn't even require you to work on the PCB, although that's not really an issue with these amps since it's easy to remove.

Thanks for the info! I clipped the bright cap and it makes a decent improvement in the tone, and a little improvement in the taper. I am going to have a master volume installed in the near future. Is there a schematic that exists for either of the 2 MV circuits you describe?