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 Forum index » DIY Hardware and Software
Single supply 4046 VCO with V/oct tracking
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kaputtpanzer



Joined: Nov 02, 2009
Posts: 134
Location: Cologne
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PostPosted: 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 Laughing
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 Cool


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ixtern



Joined: Jun 25, 2018
Posts: 143
Location: Poland

PostPosted: Wed Feb 26, 2020 6:06 am    Post subject: Reply with quote  Mark this post and the followings unread

4046 VCO is not a good idea for polysynth (until you include some kind of autotune). For analog polysynth I would go rather with 3340 VCOs.

This is my thread about 4046 in VCO:
https://www.muffwiggler.com/forum/viewtopic.php?f=17&t=222332&hilit=4046
("TH x4046 VCO V/Oct tracking with different chips")
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PHOBoS



Joined: Jan 14, 2010
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PostPosted: Wed Feb 26, 2020 6:20 am    Post subject: Reply with quote  Mark this post and the followings unread

I might try it someday, The circuit looks pretty straight forward and with easy to obtain parts, just how I like it.
Thanks for posting Very Happy

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kaputtpanzer



Joined: Nov 02, 2009
Posts: 134
Location: Cologne
Audio files: 13

PostPosted: Fri May 15, 2020 4:18 am    Post subject: Reply with quote  Mark this post and the followings unread

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 Laughing

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.


IMG_20200515_124148.jpg
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VCO Board
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IMG_20200515_124148.jpg



vcotuningtest.mp4
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Little Test after sloppy calibration

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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
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PostPosted: Fri May 15, 2020 4:36 am    Post subject: Reply with quote  Mark this post and the followings unread

Here is a little clip of some high pitched arpeggio sequence... (yes it is the stranger things theme, the ultimate testing note sequence Laughing )

With the module to the right it is already a complete little synth. The "lightGate" is a low pass gate with a switch for selecting different filter options.


vcohighpitchtest.mp4
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kaputtpanzer



Joined: Nov 02, 2009
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PostPosted: Tue May 19, 2020 2:18 pm    Post subject: Reply with quote  Mark this post and the followings unread

I built up a second vco board and I changed some resistor values in the expo converter. Within a tuning error range of +/-3 or 4 cents i could easily play from C2 till C7. It was even more precise then my Minibrute, but that one maybe needs calibration soon.
I also checked all the inputs. The linear FM works fine and can produce some crazy FM sounds. Its possible to pitch track it over some octaves. The XOR gate from the subosc/squarewave output form an logic gate ring modulator. It is nice to mix it with the clean saw wave to get some fat and droneish bass sounds. The hardsync input works, but doesn't produce very interesting sounds. Maybe i will remove this one.
Overall I am quite happy with this VCO, it works better then expected.


vcoringmodtest.mp4
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kaputtpanzer



Joined: Nov 02, 2009
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PostPosted: Fri May 22, 2020 3:32 pm    Post subject: Reply with quote  Mark this post and the followings unread

Regardless if somebody will ever look at this or not I will post the outcome of my little evening rehearsal here Laughing

And also a little picture of the setup!


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beeps_01.mp3
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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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Blue Hell
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PostPosted: Sat May 30, 2020 5:46 am    Post subject: Reply with quote  Mark this post and the followings unread

kaputtpanzer wrote:
Regardless if somebody will ever look at this or not I will post the outcome of my little evening rehearsal here Laughing


Just listened to and viewed the demos, it seems to work quite well Cool

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also .. could someone please turn down the thermostat a bit.
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kaputtpanzer



Joined: Nov 02, 2009
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PostPosted: Wed Aug 19, 2020 7:07 am    Post subject: Reply with quote  Mark this post and the followings unread

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 Laughing (thanks to TheSlowGrowth's VCO Tuner App)


vco6oct.PNG
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Around 18 cents of tuning error, when the vco gets calibrated to work over 6 octaves.
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vco4oct.PNG
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~9-10 cents of tuning errors @ 4 octaves around the middle C
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vco2oct.PNG
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~8 cents of pitch error @ 2 octaves
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vco1oct.PNG
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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
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PostPosted: Wed Aug 19, 2020 7:33 am    Post subject: Reply with quote  Mark this post and the followings unread

I tested it a few times and I found out that I can notice tuning errors down to 4 cents or less (depending on the base frequency), but to be able to do this I really really need to focus alot on the individual sound. Personally I think a tuning error of under 10 cents in total is quite hard to recognize, even if you play along with other synths. Here is a simple test to check your ability to identify a detuned note

http://www.noiseaddicts.com/2010/03/can-you-hear-like-an-audio-engineer/

Here is some theory, if somebody is interested Cool

https://bulletproofmusician.com/how-perfect-does-your-intonation-have-to-be/
http://www.peretzlab.ca/site/assets/files/1209/hutchins_musicperception_2012.pdf
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kaputtpanzer



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PostPosted: Tue Nov 17, 2020 7:21 am    Post subject: Reply with quote  Mark this post and the followings unread

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.


4046vco4oct.jpg
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4 Octaves ~ 6-7 cents tuning error
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4046vco2oct.jpg
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2 Octaves ~ 2 cents tuning error
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4046vco1oct.jpg
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1 Octave ~ Almost no tuning error
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Ayab



Joined: Oct 27, 2015
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PostPosted: Tue Dec 01, 2020 3:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

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 Very Happy
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kaputtpanzer



Joined: Nov 02, 2009
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PostPosted: Wed Dec 02, 2020 3:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks alot. Yeah a suboscillator is really a great addition for every VCO. You will get a much thicker sound!
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