Metropoulos Forum

I'm installing a Metro PTP Board in my 100 Watt 2203, i don't understand how to wire the pre-amp volume per the Metro Tech CD, anyones knowledge would be appreciated. And why do some mount the 470k resistor & 500pf cap on the board and some mount them on the pre-amp volume (mine is mounted on the pre-amp volume).

I'm not sure the pic is working, sorry, it's on the CD.

Dax, the early MV amps were built on superlead circuit boards and didn't have a place designated for the 470k and 500pf. So they put them between the gain contol and the low sens input jack.

I don't have a pic of one, can you get it from a schematic? If not I'll try to describe it.

George

I was going to go ahead and mount everything on the board as pictured on the Metro Tech CD, but im lost on wiring the pre-amp volume.

Clay finley's site has a pic of a '78 2204's guts on it -- go to the "Marshall Info" sticky post.
The http://www.tone-lizard.com site has some closer pics of that section of an early JCM800 with the resistor/cap mounted between the pot and jack as well. Just don't do the mods!!

Hopefully this pic works, it doesn't show the preamp wiring and i cannot read schematics worth a shit. i get a little flipped out when my amps gutted as it is now.

Gnugear, Anyone, you guys are the marshall circuit masters!!!

I think that pin 1 of the preamp volume goes to the 500pf Cap, and pin 2 of the preamp volume goes straight to pin 2 of V2. George, does this sound right?

Typically the circuit should go from the low input, through the 470K/470pF pair, then into the first leg of the preamp pot. The second (middle) leg of the preamp volume pot then heads off to V1b's grid. (Of course there is a bright cap bridging the first and middle legs as well, if you so desire.) The plate of V1b has it's usual 100K resistor plate load, between the resistor and the plate a .022uF coupler will branch off, go through yet another 470K/470pF pair, then on to V2a's grid.

I found the diagram you posted very confusing; since the parts weren't labelled on the board, and I'm not used to some of these parts being on the board at all, where I thought the low input might hook into the board looked like it either went to ground or input 1 already; the lack of any wires shown from the low input and preamp volume is a serious oversight if that's all the diagrams that came with the kit.

I wimped out and sent the amp to george for a mini-overhaul. New pots, new inputs, clean up the wiring and install the board. I pretty much understand the Lead and Superlead wiring, but i know nothing about the MV circuit.

Dax

Still, money well spent for a solid rockin' amp, and you can check out the circuit wired the right way until you've got it down pat.

Exactly!