Metropoulos Forum

Got this from a guy named Jerry over at PPF. Wondered what this mod actually does. Sounds like the way a MV is wired up.

MASTER VOLUME MOD FOR
FOUR INPUT MARSHALL AMP
The one single modification that has been done the most often and has the greatest number of variations is the addition of a master volume to the four-input Marshall Super Lead or Super Bass. This section illustrates the "traditional" method that most closely resembles the actual factory master volume design. It is necessary to add a 1 Meg .0. .audio taper potentiometer as shown on the facing page. In most four- input Marshall amplifiers. with the notable exception of the 200 watt Marshall Major models. the tone network is the last sub-circuit before the output driver. The wire connected to the centertern1inal on the treble sends signal directly to the output driver circuit. and it is here that the master volume pot is added. Install the master volume pot on the chassis before rewiring the circuit. making sure that you use a lock washer. or "star washer". to keep the pot firmly in place. Remove the wire from the center tern1inal on the treble pot and connect it to the center tern1inal on the master pot. Using stranded and insulated copper wire. connect a wire between the center tern1ina1 of the treble pot and the outer tern1inal of the volume pot. Connect a wire from the other outer tern1inal on the master pot to the back of the pot housing. Finally .connect a wire from the back of the pot housing to any convenient ground connection (except speaker ground) ..
The extra volume pot can be installed anywhere on the chassis that you choose. However, I reconmlend removing one of the speaker jacks on the amplifier's back panel and installing it there. Doing so gives you a hole to mount the pot in without having to drill while retaining the aesthetics of the amplifier's front panel. This also makes it easy to convert the amplifier back to stock condition, should you decide to do so later. A vintage amplifier in original condition carries a much higher resale value.

This is the type of MV that the 2203/2204 series used.
You know, the one everyone gripes about as sounding like crap with the master down......funny how it comes around full circle.
It's not the one-wire mod that you were wondering in your PP post.

Cool thanks. AH so this is the infamous mv that is supposed to be all super fizzy and shit like that? Hrmmmph... I always liked that sort of sound lol.

you can fix that mv by adding a 100-220k resistor between the wiper of the master volume and the .22 uf cap. its a cheap fix and it lowers the frequency response at lower volumes to like 33Hz or some shit. NOT fizzy at all then. darkens the tone very nicely..
mike

either of you guys know where they sell stacked pots with the dual shaft? Im out of factory holes and wouldnt mind trying this for shits and giggles.

Wow, great question. I have replaced them on mixing boards before. But they came from the manufacturer.

Some Fender Jazz basses used them, maybe CTS made some. I'll check around.

George

Yeah was thinking that it might be cool to use one of those to try some of these mods that require multiple pots being added when you dont want to drill anymore holes in a pre-exisitng chassis

yeah, great thinking, inside and outside shafts! holy damn! you can also run the pre master volume as described above with the ppimv and have a smorgasboard of tones. then if you decide you want either mv out of the circuit you just crank that knob up and remove it's influence on the circuit.
yes!
mike

myker wrote:yeah, great thinking, inside and outside shafts! holy damn! you can also run the pre master volume as described above with the ppimv and have a smorgasboard of tones. then if you decide you want either mv out of the circuit you just crank that knob up and remove it's influence on the circuit.
yes!
mike

I didn't quite think of it that way but yeah why not.

Their called Concentric pots. Allparts sells them but I think they only have one value. The only amp Ive seen them on were Dumble Dumblands. He used them to have a gain/volume control between each gain stage of the OD section. By the time you buy the pot and the special knobs your lookin at $30.

Well I know that BOSS uses them on a lot of their pedals. Im sure that they have proprietory parts built for them but still a good idea. Ill look around myself.

Mouser stocks some Alpha concentric pots, I noticed them today thumbing around ordering some semiconductors. Price wasn't too bad, less than $10 each if I'm not mistaken. I have another of their catalogs upstairs but it's late and I'm feeling too lazy to go up and get it.