Dux Hazer 8 stages optical phase shifter

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Zokk
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Post by Zokk »

The story of this project began when a friend of mine asked me to modify his phaser (a classic 4-stage FET that I can't remember the part number of) so that he could disengage the LFO and use it as a fixed bandpass filter.
The simple operation made him so happy that he asked me to build him another one.
So, as I wanted to build a phaser with optos elements for a while, I designed a first very simple circuit, without modulation, with 8 selectable stages, but with the possibility to control it with a classic expression pedal or a CV source (0-5V).
This circuit sounded interesting and I decided to expand it by adding all the options I always wanted to find on a phaser: two LFOS, envelope follower, complex routing etc...
I made a first working prototype that needed a lot of corrections, unfortunately I could never build a second prototype with the new pcbs that worked properly... time passed, and the project was shelved.
As I won't develop this circuit further, I thought it would be nice to share it here, it can be the basis of a more complete project, or a simpler one...

Several remarks:
the schematic is functional and verified, but the pairing of the optos elements is quite complex. I'm working on a measuring instrument to have clear response curves (this will be the subject of another topic as soon as the proto is functional, for the moment the java software is ok, and most of the measuring cards are ok, it remains to assemble a complete device). This measuring instrument outputs the same curves as those found on the Perkin Elmer datasheets, and will allow to test 4 vactrols simultaneously.
In the phaser you need 8! Notes on the schematic give an idea of my testing with DIY vactrols, as Perkin Elmer's VTL series are not suitable for pedals in terms of power consumption I have not even tried to integrate them.
The expression pedal/CV source input would be better suited to a programmable zener like TL431A.
The two LFOs are PICs programmed by Electricdruid.
The dual op amps are TS912INs which can drive all these LEDs without worry, they are also rail to rail.
The 56nF capacitors in the filter section also need to be matched... quite a job!

In use I will remove some functions, as the CV mixer is not perfect and some settings will shift the filter centering. Especially for envelope routing I think the knobs are useless, might as well route the envelope at 100% and just keep the direction switches (up or down).
Same thing for the CV/modulation input routing rotary selector: I think an OFF position is necessary.
The phase inversion of the CV mix in "dual" mode is not very suitable, I would also remove this function, unless you want to compensate for the filter offset inherent to this configuration.
Also the tap tempo is not very efficient: the two PICs running at different clock frequencies end up shifting (in "Both" mode).

Good luck to those who will try to take over this job. I'm a bit ashamed to give up, but at the moment things are a bit too heavy for me, and it would be a pity if it all went to waste.

Here is the first working prototype, so you can see the layout and controls on the front panel:
Dux-Hazer-proto1.jpg
First PCBs are green, second are black (but I think there is a problem with the power routing on the daughterboard, hence the non-functionnal second prototype). The main difference between the first and second prototype is essentially the filter opamps fitted on the daughterboard on the second one... maybe a bad idea:
IMG_20210621_161633.jpg
And the actual schematic:
DUX-HAZER-schematic.png

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Zokk
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Post by Zokk »

I read again my message and I said a wrong thing:
The "invert phase stuff" works in "single" mode... I had to dive again in my schematic to remember some details :?
Too complicated yeah...
so in "single" mode ("dual" footswitch not engaged) both LFOs + enveloppe follower are mixed (CV MIX A) and control all the 8 vactrols.
in "Dual" mode LFO1 + EF (CV MIX A) will control the "ODD" stages, and LFO2 + EF (CV MIX B) will control the "EVEN" stages.

Looks like this project was taylored for Dino's high skills :lol:

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Post by Jarno »

Epic project! Nice work
So you can use LFO1 to modulate LFO2? that's very nice, I've built a modular synth, and one of the things that makes those sounds interesting is "modulate everything with everything" :D
"It crackles....., but that's ok"

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Post by Zokk »

Yes there are several ways to change the rate of the LFO2, sources are LFO1, EF (positive or negative), and expression pedal/external CV.
You're right this was thought to be able to route all the modulations like on a modular synth (it has also CV in and CV out 0-5V).

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