Anti Phaser Build Report

[RickL]

I built the Anti Phaser from this page http://www.epanorama.net/schematicsforfree/Audio/Musical/Circuits/index.php

It seems to work okay, in that it sounds like a phaser, the speed control works and it's not overly noisy but from the description (The Anti Phaser is a phaser with a difference: the notch filters sweep in opposite directions.) I was expecting to hear contrary sweeps. It just sounds like a regular 4 stage phaser to me.

I've probed the outputs of both of the LM3700s and get phasing from both, I get clock ticking from both clock outputs (pin 1 of IC6a and pin 6 of IC6), I've fiddled with both trim pots, each of which has an effect, but I can't get anything that sounds like contrary motion in the phasing.

Could I be misunderstanding the schematic? I don't see anywhere where the dry signal is mixed with the phase shifted signal and I wonder if it's actually mixing two phase shifted signals going in opposite directions to get the sound. Or is the schematic missing a resistor (47k?) from pin 8 of IC2a to pin 2 of IC3? If someone with better knowledge of phaser circuits could chime in I would be grateful.

[R.G.]

I don't see anywhere where the dry signal is mixed with the phase shifted signal and I wonder if it's actually mixing two phase shifted signals going in opposite directions to get the sound.

This circuit is not a phaser in the sense that it's usually used. It has two notch filters and sweeps those notches directly, instead of using phase shift stages and then adding dry signal to get a notch. We hear moving notches as the sound made by phasers, but phase shift stages are not the only way to get that.

Or is the schematic missing a resistor (47k?) from pin 8 of IC2a to pin 2 of IC3? If someone with better knowledge of phaser circuits could chime in I would be grateful.

Pin 8 of IC4a is shown as disconnected. I believe that pin 8 of IC4a should be connected to the junction of R19, R23, R24, and R25. If you wired it exactly as shown, I believe you'd get only one phase notch, which would tally with your description.

[RickL]

I built it, as I usually do, using the 4ms cbcb method with the pcb mask included in the article. I figured that the non-connection on the schematic was a scanning glitch and tentatively corrected my copy. I'm pretty sure the pcb layout does connect those two points but I'll double check when I get home tonight.

[Mark Hammer]

Thanks for the link to that site, Rick.

Readers might want to check out this link: http://www.epanorama.net/schematics.php?url=http://www.epanorama.rackhost.net/schematicsforfree/Audio/Musical/Circuits/Wah-Wah%20Pedal.pdf

and this one: http://www.epanorama.net/schematics.php?url=http://www.epanorama.rackhost.net/schematicsforfree/Audio/Musical/Circuits/Sustainer%20for%20Electric%20Guitar.pdf

and tell me if they see anything conspicuous about the authors.

[StephenGiles]

I did a string of those which were published, just ideas which paid £20 a time when I was hard up!