MXR M-120 Auto Q

[ustompsteve]

Does anyone know about the circuit used in the MXR M-120 Auto Q. Do you know what it is based off of?

http://www.jimdunlop.com/site/products/electronics/mxr/products/m120.html

I have one that I love the sound of. So far I have been unable to remove the board from the one I have. They seem to have it glued into the housing and I am afraid I am going to break the board trying to remove it.

Any ideas.

--Steve

[Mark Hammer]

Well here is what you CAN tell us.

Look at the solder side of the board (I am assuming is is visible when the back cover is removed) and tell us how many chips you see in there and what their pin count is.

My hunch is that Dunlop retained many of the more desirable aspects of the original Envelope Filter and added some more cleverly thought-out features, such as the additional LFO.

The Envelope Filter had 3 CMOS chips, all of them 14-pin.  My guess is that you may well see evidence of 3 such chips by their solder pads, and perhaps either one or two more, or else one more and evidence of one or two 8-pin chips.   I suppose they exist but I've never personally seen an 8-pin CMOS chip.  As well, although you can always sub a pair of 8-pin dual op-amps with a 14-pin quad, most pedal makers tend to use duals, perhaps to require only a single type of item/component to be in inventory rather than duals AND quads.  So, if you see at least three 14-pin chips from the back, then I think we have an Envelope Filter as the heart of it.  If you saw only one, and a host of 8-pin chips, then I am guessing it is a different sort of beastthan the EF.

There, that's a start and no pedals were harmed in the making of this film.