Hi George, Dave and all ...
hope y'all hanging in there and doing ok
myself, I've been locked in the tool shed since early Dec working on my things ...
thought I'd give an update in the
Wayne CTP dept. since I do think about it once in a while
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I think I mentioned this here before, I took a sharp left turn in late 2017 to go back to the
EMS VCS3 synth project
that I had started w
Juergen Haible in 1995 - dunno, some strange urge came over me out of the blue ... in the course of about a year I had the whole synth sussed out including SPICE simulations of every module ... in the process of doing all this reversing I learned a few neat circuit tricks - some of which ended up as nucleus for a few of the designs shown later down below ... I needed to get away from the stuff I had been working on, including lots of Digital and some Analogue PWM circuits // ... for example I did a Univibe work-alike that runs in class-D at 140khz driving transmission gates as replacements for photo-cells ... that sorta stuff ... the last two CTP units were based on Digitally PWM'd gates as well, and felt I had milked that cow enough and needed to move on - but not before doing one last weird trial with them gates ...
as you might recall in the second phase of my CTP development (the first being the discrete jFET based analogues of the original tube modulators) I had some moderately good success using TEK465's custom Duino code to produce perfect three-phase triangle wave clock signals, embodied as digital PWM and driven into opto-couplers to perform signal mixing ... a second version doing the same but driving a bunch of bi-directional CD4066 gates worked as well, in the second case eliminating the need to match opto-couplers ... the opto-coupler version had a better feel in the end and was more compact and less wasteful from a hardware point-of-view // ... both of those Duino versions worked well
I still thought that an all-analog solution with no component matching should be possible
for about a month and a half in 2018 I toyed with the idea of wring up three OTA's as a ring oscillator, analogously to the original triode (and later jFET) circuit topology ... I started out by drawing out the 3-phase waveforms against each other and deriving conclusions about the waves' crossing points ... and went from there ... things worked but I had stability issues
... so, close !
but I had to give up as my intuition wasn't taking me to a solid place // I still think it might be a viable solution (I'm letting it rest back there for now) ...
then, sometime last year I thought of taking a radically different approach to producing three-phase triangle waveforms but starting out with a binary clock signal and running it through a Finite State Machine (FSM) to produce a three-phase binary signal set and then doing some kind of RC cheat and current-controlled amplitude stabilization to get sorta-triangle three phase signals ... but all that quickly started to look complicated with several sets of OTA's etc ...
In the process it gave me an idea of only going part-way with that transfer chain, providing a test platform so-to-speak to help show
how well tuned or balanced the constant=phase shift lattice was (without relying on BODE transfer plots and subsequent analysis) ... rather, by taking the outputs of the FSM directly and driving transmission gates as either 0 or 1 multiplier we can produce the phasors sums A, A+B, B, B+C, C, and C+A (using original Choratone schematic nomenclature) ... if A and B are phasors at 120 and 240 then A+B is a phasor lying at 180, etc etc ... so we get six points on the full 360 degree rotation of the WAYNE shifter
notice this is NOT like a BBD (chorus/flanger) with fixed delay across frequencies of interest, NOR either like a phasor/vibrato, whose phase flips 180 on either side of a phase-transition area ... instead, the WAYNE shifter does a full 360 shift on ALL frequencies across the audio band and keeps going in the same advancing direction ... I put together a cheesy video clip that shows the circuit in action fed from a signal-generator :
https://vimeo.com/427820298
definitely an exciting vid eh ... what it shows is that the 120/240 phasors are where they should be, otherwise summed together to produce the 180 phasor component and that signal mixed/summed with the input signal wouldn't cancel so well against it if the 120/240 were off ... the test does show perfect cancellation - at least at that frequency ... I still need to do more testing to confirm how far across the audio band this holds
ok, so this turns out to be useful for tuning the lattice in producing an even output across all 360 degrees of modulation ... it's fairly easy to show (by invoking independence) that if the resultant 6 amplitudes are equal then they should be continuously for the full cycle when used in a linear scenario ... that was useful and surprising in itself // I was forced to design a three-phase FSM circuit and that in itself brought me back to my University (digital design torture) days ...at least now I have optimal values for the WAYNE Lattice circuit (*!*)
with this it seemed like that might well be the end of my CTP explorations ...
that was three of four weeks ago
and then late one night, looking back at everything I had done with all this, just suddenly realized that the jFET circuit I had played with in the beginning could be made speed variable after all - and in a very simple manner ... and NOT ONLY THAT !!
it was staring at us the whole time, and not only that but the same technique can be used to make the original tube circuit speed variable as well
and so, if there's any light at the end of the tunnel I think it might be from here on ... // clearly, at some point I will be modding my two channel jFET CTP unit and mount the controller circuit in a wah shell and see how it goes ... I will post about it once I have confirmation
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in the meantime, thanks for keeping the forum open George
I'm keeping as busy as I can until work gives the green light again ... as we speak I'm going through a phase of building some novel dirt box designs - something I've avoided in the past, but came up with a cool idea I just had to try (and panning out I'm pleased to report) ... I also got a bunch of original compressors on the go and a bunch of new stuff Flanger/Chorus/ and Univibe related ... I'm also coming up with my third high-headroom low noise parametric WAH circuit ...
a year later ... for those interested:
https://viva-analog.com/viva-analog-nw- ... -jcmc2019/
https://viva-analog.com/precision-shifter-jcmc2018/
https://viva-analog.com/viva-analog-sub-mux-jcmc-2019/
https://viva-analog.com/viva-analog-hard-mod-jcmc2019/
and more to come
as for amp work, well ... (heh heh) there's my new
60w Analog Tube Amp Killer ...
https://viva-analog.com/non-linear-anal ... amplifier/
I've jammed it with a drummer ... I have to say - I've played worse !!
cheers ...
~jcm