Vox 1900 Phaser modification

This was my first venture into active-electronics. Not that it required much..

The Vox 1900 Phaser pedal is not extremely common, and I must say I have not used it much. Maybe it was voiced wrong in the factory, but I could never find use for it. Supposedly it’s identical to the 1981 Guyatone Phaser. Possibly manufactured for Vox by Guyatone.

Eventually I acquired an EH Small Stone and that kept me very happy as far as my humble phaser needs go. I like the way it sounds on keyboards as much as on the electric guitar. I’ve never tried this, but I bet hi hats sound great through a small stone as well.

Anyways, I heard of a modification common to the 1900 and that is to replace the internal trimmer with an outside pot. Here is a really bad copy of the schematics. Suffice to say I had no knowledge in electronics at the time and reading schematics was way beyond me, but locating a trimmer on the board and replacing it with a pot of the same value was pretty easy, so I went for it.

Here’s what it looks like with 3 knobs. (I replaced the old ones to match the added knob).

Below is a demonstration of the pedal at work.

Watching the video now I think it may be more sensible to wire the pot backwards. As you can see/hear, the pot makes this pedal VERY versatile. Apart from being able to control the filter’s bandwidth (12 o’clock and up), it can turn the phaser into a booster (12 o’clock and down)! Nice!