CGS combo ETI 447 audio phaser and shifty phase adaptor
While not really designed for use as a synthesizer module, it was much more convenient for me to mount this unit in the synthesizer rack than having it kicking around on the floor as an effects box.
The CGS phaser is the ETI 447 phaser in combination with a stereo phase adapter. Originally built in the seventies, the unit has spent a number of years kicking around in the junk box built into a "Memory Man" effects pedal box, only recently being rebuilt and modified to improve its performance. All IC sockets were removed, as these had all gone intermittent, and a new batch of 741's soldered in. 741's may not be the best choice for low noise, but I had them to hand, and that is what the original design used.
Modifications
Component identifiers given below refer to the original Australian edition, September 1976, ETI schematic.
A 1 meg pot was used for the speed pot (RV2) instead of a 2 meg, because I had this to hand. The capacitors controlling the speed of the LFO (C12 & C13) were reduced from 10 mfd to 4.7 mfd, and the resistor (R28) in series with the speed pot reduced from 100k to 47k. This made the range of speeds more suitable for my needs.
A depth pot was also added. A 500k pot was hung between the output of the LFO (Pin 6 IC7) and the reference "earth" (+ve of 100 mfd C4). The 1M resistor (R22) was connected to the wiper of this pot instead of directly to Pin 6 of IC7.
The design for the stereo phase adapter was taken from an "Ideas for Experimenters" article ("Shifty Phase Adapter" ETI April 1978 P99). This was also built about 20 years ago, using a couple of transistors taken from a (huge!) transistorised calculator. All parts were jammed onto a piece of perf board that was one inch by three quarters.
See also
References
- Phaser (archived) by Ken Stone, 1999, with permission of the author
External links
- Project 447 Audio phaser and Shifty phase adaptor, ETI articles
- CGS Synth discussion group, for discussion of locating parts, modifications and corrections etc.