The Trem Face Revealed

Copyright 2002 R.G. Keen. All rights reserved. No permission for local copies or display from web sites other than


The Trem Face is one of the rarest of the Dallas Arbiter products. It's kind of a mystery pedal, as so few were ever made. I personally have never seen, let alone heard one. There is, however, a schematic on the web, graciously posted at Unfortunately, I've never seen any mention of anyone ever building one from this information. To satisfy my curiosity, I pored through that schematic with my design hat on, and I decided that the schematic as drawn is sufficiently incorrect that it could never work if built as shown.

A week or two after I put the first version of this article up, I got email from Ed Crozier. Ed is a vintage effect afficianado here in Austin, and had recently bought two Trem Faces at ebay - both non-working. He offered me some bench time with the non-functional units. Thanks to Ed, I was able to confirm my suspicions about the circuit, and ferret out some items I'd missed. I now believe that the corrected circuit is indeed the circuit for a workable version of this vintage effect.

Here's my redraw of Dave's first schematic:

There are some obvious problems. The rate pot is a non-standard value, the BF2440 is an unknown part from any catalog I've ever seen, and I've never found either a 3.7K resistor or a 16K trimpot in a catalog. Furthermore, the battery as shown is connected with its positive to ground - the wrong polarity for the NPN BC184C to work.  And what's the deal with that diode across the trimpot?

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