Very simple sawtooth VCO (V/Hz)

[nicolas3141]

Another installment in my minimal modular series. This is a very simple sawtooth VCO. Barely more than half a dozen components and about one square inch of stripboard.

Designed to be easy to build, easy to understand, educational and fun. Runs fine on a variety of voltages (including battery), from +/-4.5V to +/-12V. +/-15V should be fine too, but I haven't tried it. None of the component values are too critical, so if you're building it by scrounging parts, pretty much any dual opamp should work, pretty much any diodes should work and cap and resistor values can be 50% either way without a problem.

Fun feature - touch pins 2 and 8 at the same time and the VCO will click like a geiger counter from the current through your body

Tracking is more or less linear (V/Hz) with a range of about four octaves (two octaves either side of middle C). You can tweak the range either by changing C1 or R1 and R2. Not super accurate towards either end of the range, but good enough for making fun noises and in that central couple of octaves quite capable of being played melodically via a ribbon controller like this one http://electro-music.com/forum/topic-32651.html

Cheers,
Nicolas

---

sawvco.jpg
Description:
Filesize:	58.36 KB
Viewed:	5952 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

---

[RF]

Neat stuff Nicolas! Thanks for sharing this - looks like a fun bit to play with.

bruce

[nicolas3141]

If you want the output voltage level of this to match my other VCO you should use 1N4148 diodes for D2 and D3, and increase C1 to 22nF.

With red/yellow/green LEDs there it outputs a somewhat higher voltage, but is still okay for running into most audio gear. I used yellow LEDs in mine.

With blue/white LEDs it would output a higher voltage again and you would need to be careful about feeding its output directly into other audio gear (ie other than modular synth stuff). With blue/white LEDs you would probably also want to reduce C1 to 5.6nF or similar.

Cheers,
Nicolas

[jnuaury]

breadboarded it up super quickly
turned it on... and it worked first time
the circuit is very forgiving on values as he said

i switch the cap a couple of times to make it run in LFO and supersonic territories

right now the oscillator is giving me some subtle drifts which makes for a really cool effect when you use this VCO to FM a different VCO... lots of slowly morphing modulations!

now i wont to break out a quad chip and set up two of these above audio and see what unstable heterodyning fun can be had

thanks for posting this, it of course isnt a stable VCO but the instabilty is a great "feature" that makes this a great modulation source for other more "proper" VCOs

[jnuaury]

my computer was a little unkind to me when i intended on uploading these earlier...

heres some quick sound samples before i took it apart.
no knob turning during the samples this lets you hear the instability especially in the second clip

---

nicolasVCOtest1.mp3
Description:	bc16 VCO FMed by nicolas VCO. nicolas VCO modulated by S&H	Download (listen)
Filename:	nicolasVCOtest1.mp3
Filesize:	689.1 KB
Downloaded:	3216 Time(s)

---

---

nicolasVCOtest2.mp3
Description:	bc16 VCO FMed by nicolas VCO. nicolas VCO unmodulated	Download (listen)
Filename:	nicolasVCOtest2.mp3
Filesize:	654.2 KB
Downloaded:	2932 Time(s)

---

---

nicolasVCOtest3.mp3
Description:	nicolas VCO in LFO range modulating a VCA and clocking the S&H. the S&H is modulating the nicolas VCO and the bc16 VCO. the bc16 VCO is controlled by the VCA	Download (listen)
Filename:	nicolasVCOtest3.mp3
Filesize:	672.57 KB
Downloaded:	2586 Time(s)

---

[slacker]

Those clips sound great.

I've already built Nicolas's LFO and VCLFO, with the idea of putting them both on the same panel. They already get some pretty interesting patterns going on with one modulating the other. I'll definitely be adding this to the mix as well now.

[jackdamery]

How come there is a +9v, a -9v, and a 0v ground? I'm not really sure how this would work

[jnuaury]

[nicolas3141]

I have had some feedback from someone who breadboarded one of these with a TL082 and had trouble with latch-up (it worked fine when they swapped in an LM358). It could have been specific to their situation, but be warned that TL0xx opamps may not be ideal for this circuit.

Cheers,
Nicolas

[jnuaury]

[Ojd]

edited

[Ojd]

edited

[inlifeindeath]

i built 2 of these on a TL074, awesome circuit, works great!
One issue though, when i run the output to an amplifier with high gain, the sound comes through perfect, but when i switch it to a clean channel I get really odd behavior.
When tuning the frequency, especially when done moderately fast, i get this weird 'skipping' sound. In other words, it goes from a smooth, solid wave to a choppy intermittent wave (not waveform, but amplification).
Anyone experienced this or have any ideas?
I used 4148's for all diodes and schematic values except for changing C1 to 22nf and C2 to 100nf.
Thanks!

[Ojd]

It might be this circuit need buffering/amplification, may be try different opamp, or something really simple, though I am noob, so don't rely much on my thoughts.
http://www.musicfromouterspace.com/analogsynth_new/ELECTRONICS/TOOLBOX/toolbox.html#INOAGAINCALC
Here's simple opamp calculator.

[chutneyfarmer]

Apologies for what is probably a total noob question, but I intend on building a few of these to use with a synth built from the new MFOS Experimenter Boards.

Am I correct in assuming that if I don't want the VCO to be CV controlled, and to just let it drone, I would wire +9v to the CV in on one of the pots? And if so, I could have a switch which would change between +9v and a CV input?

Thanks

[nicolas3141]

The normal way this is done is with a switched socket. Connected so that when no plug in inserted it switches to +V. When a plug is inserted, that cable provides the CV.

Cheers,
Nicolas

[chutneyfarmer]

Aw that would make sense. I've never seen switchable banana jacks anywhere though so might just have to use a normal switch. Thanks!

[inlifeindeath]

just finished wiring up a dual version with a tl074 on +/-12V and it works beyond my expectations! thank nicolas!

[frantik]

thanks for bumping this i'm go bread board it right now

[inlifeindeath]

check out the 'circuits by nicolas' sticky post. all kinds of excellent simple circuits.

[Ojd]

I've encountered some problems with the osc:
1. It is unstable in its scaling [or tracking, frequency instability was expected] (but I used ceramic disc caps, this might be the problem), but i use some software, which calculates ocs frequency and builds custom graph to play it. How to cure this problem (But I think its the caps) ?
2. When I connect osc output into CGS DC mixer, turning its corresponding level causes osc to change its pitch. Maybe output resistor (1k) has something to do with it? Or its capacitor in the osc? Also i used 358 chip for mixing, maybe higher quality opamp will cure it?
By the way i've used 104 (which is 100nf), and its a bit low. But i still get 3,5 octaves. If I put 47 nF it'l be higher an octave, right?

[Terrafractyl]

wow, just put one of these together on a breadboard.... Love it!
Mine is running on 15v with a TL082.... it doesnt track correctly though.
I used a 39k resistor instead of the 47k maybe this is the reason?

Also, would it be easy to add a Potentiometer for Frequency? If I replaced the 2 68k resistors with a dual gang pot maybe this would do the trick?

anyways thanks nicolas, I'm going to fiddle around witht this circuit a bit I think and I reckon I'll use 2 of these for a new synth box I want to put together.

[inlifeindeath]

it already has a freq pot. two pots are shown; one can be wired as a CV attenuator and the other one can just be hard wired to V+ on the CV end and you have a freq pot.

[-minus-]

Just confirming I have this circuit working with a LM358 on +/- 4.5V! Creating a virtual ground with the junction of two 100K resistors between + and - of a 9V supply.

Thanks Nicolas! I'll try more of your circuits

[Lorenzo]

what are you using for CV in??