Chorosynt Eurorack DIY

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autocet
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Chorosynt Eurorack DIY

Post by autocet » Wed Jan 27, 2016 5:15 pm

I want to make a thread dedicated to Chorosynth. I've tried in the forum EURORACK but seems out of place. Because of this I want to restart the thread here but with the DIY approach.

This is the Chorosynth
Image

I asked the author whether this assembly is free and they answered affirmatively.

This is the work actually done on KiCAD.

Image
Image

My idea is to make a new version with CV GATE, in eurorack format.

Chorosynt Analog Synthesizer actual Features:

Two and a half octaves, keyboard stylus contact with copper-copper.

Ringtones:
Souns similar to:
Larigot, Doceaba, Viola, Violin, Viola high, Cello, Flute, Clarinet, Bassoon.

effects:
Chorus, depending on the instrument
Vibrato (amplitude and frequency)
Envelopes (AR-ASR) adjustable from 1ms to 10 seconds
Pitch Control
Tuning (Pitch Center to 523,25Hz in Do second octave)

Power Supply Voltages
+ 15Vdc + 12Vdc, -15Vdc

I propose the following changes:

Projects ideas to improve the instrument:
GATE separated.
CV Adapter Volt/Oct. (CV Chorosynt original, exponential reversed)
Extra Oscillators battery. (increasing chorus effect)
Second AR-ASR (ADSR effect).
Standard Power supply.
Keyboard, independent PCB stylus for Original Chorosynt (or mono chromatic keyboard, ADSR is needed)

Nothing is perfect, I hope help and good understanding

Thanks

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Post by autocet » Wed Jan 27, 2016 5:18 pm

Because the schematic is too big to put in screen I will try to expose by functional parts of Chorosynt:

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Post by autocet » Wed Jan 27, 2016 5:19 pm

Chorosynth VCO

Image

I can think only one word, simplicity.

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Post by autocet » Wed Jan 27, 2016 5:20 pm

Chorosynth Exponential Amplifier

Image

I always think that J.D. Mitchell began designing the Chorosynth from this circuit. For this reason he christened like IC1. Maybe.

Do not many secrets to hide.

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Post by autocet » Wed Jan 27, 2016 5:21 pm

Sample & Hold

Image

Sample referenced to positive! Why?

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Post by autocet » Wed Jan 27, 2016 5:21 pm

Gate Generator

Image

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Post by autocet » Wed Jan 27, 2016 5:22 pm

Low Frequency Oscillator

Image

The same charger is the discharger of C15.
This is a triangle waveform generator.

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Post by autocet » Wed Jan 27, 2016 5:23 pm

Frequency Modulator

Image

This is a equilibrium voltage

This is a 6V reference voltage modified with Pitch and LFO controls.

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Post by autocet » Wed Jan 27, 2016 5:44 pm

Multi frequency Generator

Image

Is really the matter of chorosynt.
This circuit generates square signals since pulses from VCO.
4520 is a binary counter and generate sub-octaves, thouse are 50% pwm.
4011 will generate some 75% pwm from mixing several ones from 4520, by binary adders.

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Post by autocet » Wed Jan 27, 2016 6:01 pm

Register Keys

Image

The previous amount of frequency signals are selected by those register keys. This got the table extensive timbres. S1 to S4 are Chorus effect. Each one must be selected with a correspondent key of instrument. Larigot and Doceava are not choros effect. The rest depends on the height of the instrument.

Finally filter are modifying ring subtracting high harmonics.

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Post by autocet » Fri Jan 29, 2016 3:34 pm

Image

Enough for a stylus instrument. Should be modified to a keyboard instrument.
Last edited by autocet on Fri Jan 29, 2016 4:18 pm, edited 1 time in total.

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Post by autocet » Fri Jan 29, 2016 3:48 pm

Image

And finally a VCA in the style of the rest of the synthesizer.

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Post by sduck » Fri Jan 29, 2016 4:49 pm

Demo? What does it sound like?

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Post by autocet » Sun Apr 09, 2017 3:47 pm

Some one experiment with chorosynth?

I wants made this not alone.

I have news.
pm

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Re: Chorosynt Eurorack DIY

Post by audiomirage » Wed Apr 22, 2020 9:51 pm

Well, it's been awhile since this project was started, but I've finally caught up!
Has there been any progress on this build?

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Re: Chorosynt Eurorack DIY

Post by autocet » Sun May 17, 2020 5:22 am

Very sorry for my delay.

I consider to me an expert in the Chorusynth of J.D. Mitchell. I will explain to you the big amount of adventatges and desagriments that I have been in past with this machine.

Perhaps, I will be to build a other version of the Chorusynth. I will thinking try a digital one of it and because that I was writing this article: (Sorry, this is in Catalan, my mather language, but I consider graphics are enough explaning my idea.

https://www.autocet.cat/octave-7/

In other hand, this was a large thread that I run in Hispasonic, I consider it for interested many people.

https://www.hispasonic.com/foros/corosi ... 981/476901


I do a "moogle" translation of the last post in this thread in Hispasonic that I resume the must important stuff to consider. Corosint was the translation in spanish of the Chorousynth word.


<<<< News ... or rather, problems found in the Corosint.

As I mentioned a while ago in this same thread, I had a lot of problems with the circuit and due to lack of time I never finished finding out what was wrong with 100%. Although I haven't had much more today, I hope I have resolved those issues. So, please take up the issue of goodwill.

1.- The portamento or glissando C1 capacitor should works as an analog memory, a Sample & Hold as it is usually called. However, as it is physically built it is prone to drift problems. A first solution would be to bring it closer to pin 3 of IC1 and in the case of requiring lacquering of the PCB board, omit the lacquer in this area of ​​the capacitor, since these products leak because they are not perfect insulators. It is also recommended to enclose the track of said pin 3 with the capacitor and the P2 output to ground. That should be discussed more closely since the ports are with capacitor to ground, instead here C1 goes to + 15V and it is not clear if it would not really be a problem to enclose to ground, to + 15V or anywhere. Without approaching pin 3, without lacquering or track closure it works for me with the specified 470nF capacitor, but it is clear that this is a problematic circuit.

2 .- During the fall of the envelope the frequency of the oscillators is increased some semitone. This effect is noticeable by increasing the drop factor in P11 and has caused me a lot of headaches. At first he attributed it to the previous defect (1). But at present it is already located and therefore you can bet on some solution: The defect is caused by R81 through the + 12V supply, which despite being stabilized, the excess load causes an apparently insignificant variation, but sufficient to raise the general frequency of the oscillators. The most logical solution is to feed part, on the other hand it would seem sufficient to increase the value of R81 to values ​​of 10K, but that would spoil the operation of AR with C35 of 47nF since an unwanted Sustain would appear. Following the path of raising the resistance you should change C35 to a lower value and add a buffer to decouple the IC18 logic gate load, which would be a very big change in the circuit.

3 .- The vibrato does not disappear completely when P4 of the amplitude of the vibrato is completely closed. Again, the effect of variations in a circuit also located at + 12V affects the supply voltage of the oscillators and therefore their frequency. I have simply changed it to + 15V and the effect has disappeared. Of course, this solution is incomplete since the vibrato frequencies change, and C15 and possibly R16 must be changed to readjust to the original values.

4 .- The isolation between oscillators is very important. The decoupling of inductors L1 to L4 may not be sufficient, which is why the tracks are so long in delivering power to these oscillators, acting as absorption resistors. It is possible that a 10 ohm resistor in series with the inductors is a good practice, but this shows me, from the above defects (2) and (3) that powering the oscillators separately would save a lot of headaches (even building them in separate plates with independent ground planes).

With these "mutations" it begins to have an acceptable quality as a musical instrument. It would be necessary to achieve more dynamics in the envelopes and the control of oscillators at volts per octave.

Grateful for your attention. >>>>

I also I will be grateful of your attention,

Jordi Breu (alias Autocet)

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