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kaputtpanzer
Joined: Nov 02, 2009 Posts: 139 Location: Cologne
Audio files: 15
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Posted: Fri Feb 21, 2020 5:57 pm Post subject:
Single supply 4046 VCO with V/oct tracking Subject description: ...with sub oscillator, fm, ring modulator and hard sync! |
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Hey hello,
I would like to share a schematic with you, from the VCO I was working on the last weeks. The expo converter is a true classic, based on that electronotes article from the 1980s. It can also be found in Rene Schmitz's 4069 VCO. It's basically a single supply version of that one, with some modifications. It's also using a ntc resistor for temperature compensation (Rene's notes about ntc resistors in expo converters are very interesting btw).
Before I started working on this VCO, I had a look at Thomas Henry's X-4046 VCO. I modified his idea of the sync input and used it for my VCO. But I didn't use the XOR gate of the IC for the sync. Instead I used it as a simple XOR ring mod, which effects the square wave output. It should be mentioned, that the saw wave output has double the frequency as the square wave output. Though the square wave output can be used as a sub oscillator, for nice and thick bass sounds.
The V/oct tracking is working mediocre, but it is quite useable. Maybe not for unsion play, but it's good for basslines or drony leads or even some chords. You can expect 3 - 4 octaves in tune ("in tune" means you have to live with around +/- 3 cent tuning error, which is very acceptable for me). Of course the more time you spend on calibration the better the performance will be, it can be a bit tricky to get the best possible performance. For good tracking you will need Philips or NXP 4046s, other brands like Texas Instruments will not work well at all.
Tell me what you think about it
Btw I have gerber files of this VCO. I will test my design and then will put it online. When ordering with pcbway or so, you get 10 VCOs for 5$. Maybe that is a good start for a poly synth
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ixtern
Joined: Jun 25, 2018 Posts: 145 Location: Poland
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PHOBoS
Joined: Jan 14, 2010 Posts: 5591 Location: Moon Base
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kaputtpanzer
Joined: Nov 02, 2009 Posts: 139 Location: Cologne
Audio files: 15
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Posted: Fri May 15, 2020 4:18 am Post subject:
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Sorry for answering so late. The PCBs finally arrived and look pretty nice. I made one or two little mistakes and also the sync is not working as expected (I think its missing a coupling capacitor), but beside that it's a neat little module. Thanks ixtern for the analysis of the 4046, I made very much the same experiences. The 4046 can deliver around 3 quite solid octaves (+/- 2 cents tuning errors) and not much more. I want to use it for basslines and simple leads and maybe also for some supersaw sounds and I think its perfect for that. It also works quite well with eurorack and my semimodular gear. I attached a little videoclip that shows the capabilities in the lower octaves, but its pretty much the same in the upper octaves if you stay under C7. Its missing a HF correction, so its not suitable for the very high octaves, but I think i never played something over C7 anyways
Though for Polysynth I will look into something else. Maybe a digital solution. Electric Druid's wavetable VCDO looks awesome and comes with alot of features...
@Phobos: I can send you one or two boards over if you want. But I would first make the corrections to the circuit and also design a frontpanel. But this will take some months hehe.
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Little Test after sloppy calibration |
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vcotuningtest.mp4 |
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Last edited by kaputtpanzer on Fri May 15, 2020 12:59 pm; edited 1 time in total |
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kaputtpanzer
Joined: Nov 02, 2009 Posts: 139 Location: Cologne
Audio files: 15
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kaputtpanzer
Joined: Nov 02, 2009 Posts: 139 Location: Cologne
Audio files: 15
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kaputtpanzer
Joined: Nov 02, 2009 Posts: 139 Location: Cologne
Audio files: 15
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Posted: Fri May 22, 2020 3:32 pm Post subject:
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Regardless if somebody will ever look at this or not I will post the outcome of my little evening rehearsal here
And also a little picture of the setup!
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Two of my 4046 VCO and two low pass gates playing together. A pure data patch is sending them notes in a randomized order. |
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beeps_01.mp3 |
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blue hell
Site Admin
Joined: Apr 03, 2004 Posts: 24079 Location: The Netherlands, Enschede
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Posted: Sat May 30, 2020 5:46 am Post subject:
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kaputtpanzer wrote: | Regardless if somebody will ever look at this or not I will post the outcome of my little evening rehearsal here |
Just listened to and viewed the demos, it seems to work quite well _________________ Jan
also .. could someone please turn down the thermostat a bit.
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kaputtpanzer
Joined: Nov 02, 2009 Posts: 139 Location: Cologne
Audio files: 15
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Posted: Wed Aug 19, 2020 7:07 am Post subject:
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I am still working on this thing though. I just thougt that I maybe will make another version of this vco and add a vc pwm waveform.
I finally found some time to do some measurements on how accurate this vco is and it turns out that it is really not that accurate. But on the other side it's also not that that bad, for a vco with the most simple expo converter. Some notes will always be a bit off but overall it can be calibrated to work over a few octaves. it is obvious that playing in unison is off the table, you will hear the notes beat against each other (which is good for some supersaw sounds hehe)..
Here are the results (thanks to TheSlowGrowth's VCO Tuner App)
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Around 18 cents of tuning error, when the vco gets calibrated to work over 6 octaves. |
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~9-10 cents of tuning errors @ 4 octaves around the middle C |
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~8 cents of pitch error @ 2 octaves |
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~5-6 cents of tuning error @ 1 octave (here it shows that some notes are always a bit off, otherwise the tuning error would be less than 3 cents) |
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kaputtpanzer
Joined: Nov 02, 2009 Posts: 139 Location: Cologne
Audio files: 15
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kaputtpanzer
Joined: Nov 02, 2009 Posts: 139 Location: Cologne
Audio files: 15
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Posted: Tue Nov 17, 2020 7:21 am Post subject:
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I know not alot of people are interested in this, but I am still working on this VCO and I somehow have to say that it's worth it. Today I used another midi2cv interface to measure the tuning accuracy again. I had the feeling that the one I used before wasn't that precise, because also other synths had problems to stay perfectly in tune. What I measured is really satisfying.
Over a span of 4 octaves the tuning error will stay around 6 cents and over one or two octaves there is almost no pitch tuning error at all. I never expected those results from an analog VCO, that can basically be powered by a 9V battery. I am very happy about this.
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4 Octaves ~ 6-7 cents tuning error |
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2 Octaves ~ 2 cents tuning error |
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1 Octave ~ Almost no tuning error |
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Ayab
Joined: Oct 27, 2015 Posts: 180 Location: London, UK
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Posted: Tue Dec 01, 2020 3:42 pm Post subject:
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I listened to your demo's and it sounds really good. Useful to have the ring mod and sub octave options that are not found on many VCO's. Good work |
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kaputtpanzer
Joined: Nov 02, 2009 Posts: 139 Location: Cologne
Audio files: 15
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Posted: Wed Dec 02, 2020 3:03 pm Post subject:
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Thanks alot. Yeah a suboscillator is really a great addition for every VCO. You will get a much thicker sound! |
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