VFE Enterprise / Tractor Beam notes

[Aentons]

I found this explanatory post from Peter at VFE on another forum and though I would post it here:

https://www.thegearpage.net/board/index.php?threads/vfe-enterprise-phaser.1019113/

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Jul 1, 2012#18
VFEpedals
VFEpedals
Member
Messages:112
Joined:May 24, 2011
Location:Puyallup, WA

Here's the skinny on the Enterprise:

I began messing with the Phase 90 circuit a few years back, and really liked some of the sounds I was getting out of it. As with all of my designs, I like to squeeze every ounce of goodness out of these circuits, so here's what I've done:

1) Added a feedback control that takes the phaser output & feeds it back to either the 1st (positive) or 2nd (negative) phaser stage. At noon, it feeds both evenly, and will yield zero feedback like the original 74 version.

2) Changed the output section just a little to get a full range MIX control. The output section uses 1/2 of an OPA2134PA op amp. This essentially has the same purpose as the output transistor in the 74 version, but allows for much easier output level control via the internal trimpot.

3) The STAGES switch basically changes phase stages into inverting buffers. With 2 stages, there are 2 inverting buffers...meaning no inversion, and 2 phase stages. This is like adding two buffers to the Phase 45. With 3 stages, there is 1 inverting buffer & 3 phase stages. This gives the phaser a mellower "backward" movement. 4 stage is just like a Phase 90.

4) The MODE switch toggles out a set of capacitors in two of the 4 stages. In phase mode, all the capacitors are matched, yielding a focused phase sweep like the 74 Phase 90. In vibe mode, two of the stages are matched & the other two are very different. This yields a washier, less focused sound. The uneven phase sweeps is the core of what make the Univibe sound the way it does. While the V setting isn't intended to replicate the Univibe, it does get a similar sound.

5) I added a charge pump for more headroom. The JFETs are still a HUGE limitation, so there is not much that could be done, but I did whatever I could. What this also means is that the LFO has a much wider sweep, so you'll have to pull back the DEPTH control some to get that 74 sound.

6) I added a DEPTH control, but that's not a unique feature to the Enterprise, lots of people are doing that to the original Phase 90 circuit.

There are other things that are changed, but they have to do with switching, power supply filtering, and better op amps, which make very minor differences in the phase sweep.

I hope that helps!