Inverted phaser - worth it?

[auden100]

I've been dreaming of building a phaser again, and while hunting for clues and mods came across the Pigtronix EP 1 & 2.
Andy tries the inverted signal at about 7:30.
https://youtu.be/OsJXfDKpbpw

So two questions arise.
1) Is it really as easy as just inverting the phased signal before it's mixed with the dry?
2) I haven't found any good A/B comparisons of the two sounds, so is there anyone with experience who can verify whether it's worth the trouble?

Thanks.

[robthequiet]

From the description, the switch is between the phased signal summed versus differenced. I couldn't really hear much difference, it seems that the other controls have a more pronounced effect, but probably just Youtube sound quality not doing it justice.

A phaser by definition changes the phase of the signal, so theoretically if you invert the effect you would be combining at different phase differences anyway, which are being modulated  -- plus you can widen the phase difference resonance and filter, so to me the phase inversion is not the strongest thing you can do.  The notch hits the signal at a certain point and wobbles back and forth. But if they went to the trouble of adding that to the circuit, maybe it does more than the video suggests. My 2 pence. 

[auden100]

Thanks for the feedback. I agree. It doesn't seem like the strongest option from the video.

If I understand you correctly, I would mix the two signals via a differential amplifer rather than the summing one. So starting with the Causality 4/6, instead of hacking in a whole different opamp, I could consider doing some component and connection switches with the already present number?
http://www.diystompboxes.com/smfforum/index.php?topic=80456.0

[Kipper4]

http://www.diystompboxes.com/smfforum/index.php?topic=114633.0

[auden100]

I don't follow, kipper. I'm not actually intersted in an envelope filter. Just wondering about the "inverted" function of the EP. Am I missing something?

[Kipper4]

This came out of the enveloped phaser

the IC3 A input switching made a big difference in sound



Dont take my word for it put it on the breadboard.

[anotherjim]

Kippers drawing show a good way to do it. Inverted mixing it is, which is what we think you are asking for.
It ought to be a very big difference in the sound.
A phasers phase shift is also a very small time delay, so some of the signal, bass especially, is not moved much, if at all, in respect of the clean signal. So mixing the clean signal with the inverse of itself results in silence, and the only sound that makes it out is the difference between the clean and whatever did actually get phase shifted.

[StephenGiles]

There would, I believe, be a more drastic difference in the sound if a few fixed phase shift networks are worked into the dry signal path - a la Aphex Instant Phaser !

[Kipper4]

More phaser stages and an odd number in the regen?feedback would definitly be a more intense phaser sound.
I just did it as a small footprint, low part, optical alternative to fet matched p45.

[nocentelli]

.. is there anyone with experience who can verify whether it's worth the trouble?

Thanks.

I owned the ep1 for a while, and can report that the invert switch does make a noticeable difference, but of the "more/less pronounced" type of effect; It doesn't radically alter the character of the sound per se but alters the proportion of swoosh audible in the mix.Well worth the cost of an extra switch on a tricked out DIY build, IMO.

[Mark Hammer]

The DOD FX20 is purportedly a "stereo" phaser and provides an add and a subtract output.  The two outputs cancel each other in air so it is really only used as stereo in a studio setting, and one output at a time on stage.

Both outputs sounded different enough to warrant their existence, however where regeneration/feedback adds something to the character of the one version it actually adds nothing to the other.  On the other hand, that may be a function of the manner in which feedback is provided/routed.  In something like the Phase 90, feedback goes from the 4th to the 2nd phase-shift stage, such that the feedback is purely wet signal, which is then added to the dry.  In the FX20, the same wet signal is fed to the add and subtract mixer/output stages (U10a, U10b), but the feedback goes from the 4th phase-shift stage back to the input stage (U4a).  In other words, when the wet signal is added to and subtracted from the dry signal, it has already impacted on the dry signal prior to mixing, which may have something to do with the outcome.  I would imagine that if all feedback were contained within the wet path, as occurs with the Phase 90, adding and subtracting the wet signal from the dry signal would still permit productive use of feedback in both modes.

[Transmogrifox]

My personal favorite is option to invert feedback.  With enough phaser stages you can do that by selecting between an odd or even phase stage to get or inject feedback (regen) or just put Kipper's phase inverter in the feedback for a subtly different effect.

My digital phaser code gives the option to do any combination of positive or negative feed-forward or feedback.  Both make a distinct effect, and combining the two in different ways I would think is worthwhile...but I'm a tweaker.

[auden100]

Great. Thanks for the input, everyone, and Kipper for that handy schematic. I'll try some of this out and post the results. Realistically it'll take a few weeks.