Joined: Nov 29, 2008 Posts: 652 Location: Berlin by n8
Audio files: 23
Posted: Thu Jun 28, 2018 10:27 am Post subject:
gate/cv sequencer using only one potentiometer Subject description: and some (cheap) pushbuttons
i have many of those little pushbottons left,
so i was thinking about how to use them in a sequenzer,
attached an idea for a gate sequenzer,
one had to push two buttons at a time to programm it, set or reset button and the desired step button
on the gateout one could attach a 4017 with pots to have CV, whitch has the atvantage that the CV would stay until the next gate impulse comes
the caps will decharge over the time but it will take a long time until they go under 0,6V (one could use smaller caps to add somekind of randomness when the seq starts to forget
cu, gabi
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Last edited by gabbagabi on Wed Jul 25, 2018 9:01 am; edited 2 times in total
get rid of the TL071 and use a noninverting buffer (spare gate, or 2 inverting in series) instead. With a feed forward resistor of 100k between in and out of the buffer the caps (100nF then) will "autorefresh" forever.
I have a similar touch sequencer: Instead of switches there is a SET and a RESET touch input. each connected via diode to the storage cap.
SET diode direction is cathode to cap, RESET diode is connected anode to cap. And there is TOUCH electrode connected to a square wave oscillator. When I touch this electrode with my left hand and either a SET or RESET einput with the right hand, I can program the sequencer.
cap values must be small (nF range) because skin resistance is high. A more reliable solution is to use a "stylus" conneted to the square wave osc. and touch the SET/RESET inputs with it. Then100nF caps are ok.
Joined: Jan 14, 2010 Posts: 6058 Location: Moon Base
Audio files: 728
Posted: Sun Jul 01, 2018 4:02 am Post subject:
I'd go with some flip/flops too. Besides being more reliable you can toggle between set/reset with a single button.
The comparator on the output is not a bad idea in this case.
elektrouwe wrote:
With a feed forward resistor of 100k between in and out of the buffer the caps (100nF then) will "autorefresh" forever.
Does anyone know the sequencer of the Leploop V1? I think switched capacitance analog shift register is used there. This term was until today a bit mysterious to me. Thanks friends!
...Leploop V1? I think switched capacitance analog shift register is used there. ..
didn't know this sequencer yet. google found " the LEPLOOP has a 16-step analog recorder, much like an analog delay.Over time, as the analog sequencer cycles through its pattern, the signal will degrade and the sound will hange. This is because the capacitor can only store the signal for a limited amount of time"
for a step sequencer storing only 0V and VDD, refreshing the memory is easy with a noninverting Schmitt-Trigger as described above. For real (quantized) analog storage you would need an ADC that reads
the actual (already slightly drifted) analog voltage and refreshes the original voltage with a DAC. I've sketched a 3bit solution with 8 comparators and a 8/3 decoder as ADC and a 4051 with linear R string as DAC.
But in microcontroller days it's too much effort to do it Lunetta style. Last edited by elektrouwe on Wed Jul 04, 2018 12:31 pm; edited 2 times in total
Clearly, I understand. But I find MUX as bidirectional switch for read/write operation very simple, useful. During ~10% of CV step duration to read voltage by S&H, then during 90% of CV step write its value back to capacitor. At output will be while whole step duration still right CV value. Maybe 4066 switch or FET controlled by short monostable triggered by clock. Touch sensitive CV sequencer that´s exciting idea. To be able to "tune" sequences on the fly with finger pressure, something like to inflate tyres at pump +/-! Impro friendly piece of gear.
I've made a leaky gate sequencer for my soft synth .. its doing nice stuff .. but am not totally happy yet with the forget curves .. too abrupt ... also I want negative forget .. negative leakiness ... as in that it can grow back from sparse to the programmed pattern. So still experimenting a bit with it .. but what a nice idea :-)
Joined: Nov 29, 2008 Posts: 652 Location: Berlin by n8
Audio files: 23
Posted: Fri Jul 20, 2018 3:54 am Post subject:
elektrouwe you are the master!
the feedback idea is just amazing!
I took the idea for the one-pot-cv-seq on a breadboard-ride.
first i tried 100nF caps and a 100k feedback resistor, with this the CV went slowly but noticable up.
So i tried something bigger 47µF and 1M- which sounded stable. Ive did a recording of 18 minutes, and it came out that with this combi the pitch is going down, but veeeery slowly. So adapting the C/R combi will stabilize the drift more, or one could use a pot as feedback-resistor to make the drift variable
attached a soundfile which shows the pitch-drift over the time: 0min, 6min, 12min and18min.
cv test.mp3
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one-pot-cv-sequencer-gabbagabi.png
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I like the idea of sequencers that forget 
