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EH Polyphase

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8/19/1999 8:18 AM

EH Polyphase

Hi !

I've dreamt a long time of the Mutron Bi-phase. Since I've seen and heard this rare Electro Harmonix Polyphase at Tonefrenzy, I just can't sleep anymore. All those strange knobs, all those liquid sounds !!!

Has anyone the schematic of this box ? (maybe in R.G.'s Superfun Attic ...)

Or could anyone explain me how it works so I can design the same kind of effect? (enveloppe-controlled-phaser? I've also seen an enveloppe modulation control on it)

8/19/1999 1:29 PM

Three aspects to envelope-controlled phasing.

1) Sweep itself is driven by the envelope: This is simple to do. Use a photocell-based phaser design, and drive the LED coupled to the photocells with an envelope detector. You could easily adapt the Mutron design by substituting phase shift stages for the state-variable filter in there already. Also done with FET's but this requires more tinkering.

2) Sweep RATE is driven by the envelope: I think this is what the Polyphase does. Essentially, you set an initial sweep rate, and the control-voltage from the envelope detector is summed with the existing control voltage that drives the sweep LFO.

3) Simultaneous driving of sweep width and rate: Same deal, only your envelope detector sends a control voltage to two different paths, each of which could be mixed in to taste. E.g., picking strength would have a small effect on sweep rate, but a more substantial effect on sweep width.

As an addendum, 20 years ago, when Craig Anderton was publishing DEVICE magazine (the table of contents of which are supposed to be archived here at AMPAGE), he designed different modules for a guitar processing system that was intended to produce synthesizer-like control without doing pitch extraction. One of the modules was a "pluck detector", that summed indicators of pick attack (which could be either trigger pulses coming from a trigger extractor) over multiple plucks, to produce a control voltage that varied as a function of how many notes your were playing (i.e., how fast), rather than how strong each pluck itself is. Something like this is probably more appropriate to driving the LFO rate of a phaser than the standard envelope detector.

8/19/1999 4:55 PM
Arnaud	Thank you for this information, Mark !

8/20/1999 9:17 AM

quote:
"..the table of contents of which are supposed to be archived here at AMPAGE.."

It's still here, Mark. Just enter 'device' as a search term in the box on the front page.

--tboy

8/21/1999 6:15 AM

from my origional Polyphase manual:

Controls

FOOTSWITCH: Alternately connects effect (phasing) or direct unmodified signal to the OUTPUT jack.

SWEEP/ENVELOPE SWITCH: In the SWEEP position normal phasing is obtained and only the RATE and FEEDBACK controls have any effect. In the ENVELOPE mode the phasing is controlled by the signal level from the instrument through an envelope detector circuit. In this setting the RATE control is inoperative but all others work.

RATE CONTROL: Varies automatic sweep from very slow to rapid. As the rate is increased the sweep range decreases to maintain a smooth musical quality of effect.

FEEDBACK CONTROL: Usable in all modes of operation, this control introduces positive feedback for added color and emphasis of the phasing effect. High feedback is desirable for very slow automatic sweep and for adding a vocal quality to the envelope detector controlled sweep effect.

ENVELOPE SENSITIVITY CONTROL: In the ENVELOPE mode the phasing sweep is controlled by the signal level from the instrument and is therefore controllable by how hard the instrument is played. When this control is properly set, soft playing should produce a slow rise and fall of the phasing effect; but sudden, hard playing should produce a fast rise followed by a slow fall. How far the phasing sweeps, how quickly it rises and how it is damped are all player controllable. When used with high FEEDBACK, some remarkable voice-like effects can be obtained.

ENVELOPE MODULATION and MODULATION RATE CONTROLS: These introduce a phasing modulation superimposed on the envelope follower effect. This permits a variety of effects ranging from beautifully subtle to extremely bizarre.

Incidently, ROLAND/BOSS's Phase V does the same envelope controlled rate thing without the extra ENV MOD and MOD RATE controls.

8/21/1999 9:02 AM
Arnaud	Very helpful information, Rick ! (especially about what the envelope controls) Thank you !

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