A small analog mono synthesizer...

kaputtpanzer

Since a year or so I fantasize about developing a series of small analog synthesizers, that will fit in guitar pedal or other types of enclosures, with frontpanels made of FR-4 pcb material.
The synthesizer I am about to describe is basically the archetype and prototype for the more advanced synths. The next one will be based around Electric Druids VCDCO and TAPLFO chips and another one will include the famous CEM3340 vco ic paired up with a vcf that is a weird mixture between a Wasp vcf and an Oberheim Sem vcf.
But let's have a look on the first one of these synths. The main goal for me was that it can fit into a small aluminium die cast enclosure, without the need to use smt componentes or small 1/8 watt resistors. This meant I needed to have a low parts count. The result is that I used the most basic circuits for each individual function and merge them together into one circuit.
I really did not expect much from it, but I am actually very suprised that the output of this progress is much more versatile and interesting (but with a nice and big "oddness-factor") than I thought.
Though I took my HEF4046 vco design and built all the other stuff around it. I decided to take the most simple vca design I know which is the infamous single diode "vca", that is often used in lunetta-type synths. I was suprised that it is actually working with sawtooth waves aswell. It gets a bit weird and distorted when the envelopes fade in or fade out, but I really like the sound of it. Since my vco design has a sawtooth output that is one octave higher than the squarewave output, the squarewave output can be used as suboscillator.
Both waveforms are mixed together and send in to the vca, which comes before the vcf.
The vcf should actually have been a twin-t notch filter, but I kicked out the highpass part and it became a low pass filter, which has quite some similarity to tim escobedos q&d vcf. This thing sounds dirty but when you use the right values for the components it can be tamed and can sound quite creamy at high resonant settings.
For the envelope generator I actually planned to use a 555 timer ic, but that would have had to many components. Though I decided to build the most simple envelope generator that just contains a comparator at the input and a buffer at the output. It's not perfect, but it works just fine.
There is no modulation for the vcf beside the envelope modulation, but this alone sounds super nice (there will be a jack for cv).

There are some downsides to this simple circuit:
* The "vca" is not a real vca and distorts the signal (which I actually like)
* The "vca" has some signal bleedthrough, which is gone when using the env mod (but this could also stem from groundloops and my messy breadboard built)
* The vco is not very precise, but works solid over 2 to 3 octaves or even 4 octaves
* The envelope generator is not that good but if you are aware of its sweetspots it can do a good enough job
* There is an overall oddness to some controls, but it works much better than I expected
* It has no midi (only cv)

The pros are:
* The gerber files will be available for free
* It will be very small for a fully functioning, east coast style analog synth. It is literally half the size of a korg volca device
* It has a suboscillator
* The output is actually quite powerful and it "sounds big"
* It sounds unique and quite versatile
* It can be hooked to other (semi)-modular devices.
* You can play it polyphonic when using several of those synths and a multichannel midi2cv interface
* Built cost will be under 50€($)
* I developed the synth in 5 evening sessions or so Laughing

I added the schematics, a render of the pcb and two sound clips.

Gerber files will be uploaded in spring and I will most likely sell some pcbs and frontpanels.

If you want to leave a feedback I will be very happy about it...

monoTeaserA1.mp3

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Some bass sounds with full resonant setting and also with resonance dialed a bit more down

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monoTeaserC1.mp3

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Arpeggio with half open filter and low resonance

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monoTeaserB1.mp3

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Some high resonant arpeggio sounds that sound like an angry duck :P

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monoSchematics.png

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The schematics so far. Sorry for the mess :)

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1590mono.png

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A render of the pcb

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phobos · Posted: Fri Jan 15, 2021 8:47 am Post subject:

nice design, sounds great! Razz

kaputtpanzer · Posted: Fri Jan 15, 2021 4:50 pm Post subject:

Ahhh Phobos great that you write. I wanted to ask you something... Cool

Are you interested in collaborating with me and build a barebone version of your midi2cv converter? A version with a dip switch for channel selection and without the encoder? I could design a nice pcb and frontpanel for the 1590B enclosure.

I could pay you in pcbs and frontpanels Laughing

I guess I could do it myself, but I guess for people that are more used to coding it will be just a quick finger exercise to rewrite the code.

phobos · Posted: Tue Jan 19, 2021 12:05 pm Post subject:

I've send you a pm Wink

kaputtpanzer · Posted: Mon Mar 22, 2021 5:39 am Post subject:

The first version of the circuit boards arrived a while ago. There are a few little issues here and there, but besides of those it all works, looks and sounds much better than I expected. I uploaded photos that shows the initial prototype and also 2 audio demos...

lilprotoA.mp3

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testdrive using a sequencer...

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lilprotoB.mp3

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a more experimental attempt with some AM using another oscillator, creating weird experimental dupstep sounds :)

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lilproto1.jpg

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lilproto2.jpg

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lilproto3.jpg

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AlanP · Posted: Sat Mar 27, 2021 11:21 pm Post subject:

That is super nice, and I would be keen on buying a PCB from you Smile

The only thing I'd do differently is to jack mine up for standard 9V center-ground Boss pedal power supplies.

Any issues with the threading for the 3.5mm jacks and the 1590BB enclosure? Do they go through enough for the nut to grab them?

RykAntoniuk · Posted: Fri Jul 15, 2022 1:30 pm Post subject:

I love the sound of the unit! Great timbres from the VCF that you added to it! Together, a very liquid’ish sound! Especially with the amplitude modulation from the external oscillator!