Copyright 2002 R.G. Keen. All rights reserved. No permission for local copies or display from web sites other than http://www.geofex.com.
|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 foxrox.com. 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?