Hello everyone .
I am only 15 years old (I am French therefore some translation problems …) and I launch out for the first time in the manufacture of some modules.
So I start making a 1V / oct VCO using this :.
It’s not exactly Sam’s version, but this one suited me at the capacitor level. after realizing it, I tested it with an oscilloscope. It only oscillates every two seconds and that’s it. The rest of the time I have nothing. The output that should give me a square wave works (it works but every two seconds :() while the other two outputs give me nothing that looks like a triangle wave or sawtooth. If I change the frequency I Nor do I have the impression that it changes anything …
My editing seemed good to me but I could send you photos if necessary …
Thank you in advance I think it’s great to be able to communicate with other people who can provide solutions to my electronics problems !!!
So a big thank you to this forum and for your solution!
Enoha Roubaud
So it oscillates, but not a lot? I assume you’ve checked the component values, but you may want to check the main oscillator cap again, just to be on the safe side (the capacitor connected to pin 11, should be a good 1 nF capacitor between the pin and ground).
Another possible option is that you simply don’t have enough CV in to the CV mixer (pin 15). With the usual component values, you need around 9 V in total (from all CV sources combined) to hit 440 Hz (see the chart below, from here).
You cannot measure this on the pin itself, but if you measure the voltages on the other side of each 100k resistor and sum them up, you should get the total CV.
hey!!! good to hear your giving it a go 
great news. do you have a schematic?
it depends. you may be fine and it may be working its just very the 1v/oct input could be offset very low. which circuit is it? is it the super simple one? or the CEM3340?
oops I forget the link of the schematic 
:http://modular.ob1techno.com/2019/04/04/alfa4-vco-prototyping/
salut @Enoharduino , j’ai fait exactement ce circuit, et il fonctionne bien, donc déjà ça ne viens pas du schéma.
c’est peut être bête comme question, mais si il fonctionne mais très lentement, as tu essayé de réglé le trimmer ?
ou peut être une erreur de composant ? vérifie peut être ça au multimètre comme dit @fredrik
Traduction : hi @Enoharduino, I did exactly this circuit, and it works well, so already it does not come from the diagram.
it may be silly as a question, but if it works but very slowly, have you tried to adjust the trimmer?
or maybe a component error? maybe check that with the multimeter like @fredrik says
So that looks like Sam’s simple layout with a few minor tweaks. I’ve marked the cv source voltages below. Measure them either at the resistors (A) or near the wires (B) relative to 0V (eg the rail marked below):
Hi! In fact between gnd and the resistance of the CV input I have about 7.5v but if I do the same with the resistance just below I have 0v.
So last night I tested the VCO with my MIDI keyboard in CV input and it works!
I have indeed a good oscillation (whether for a square wave; sawtooth; or triangle).
My problem now is that the frequency and the pulse width cannot vary. Only PWM seems to work …
I assume you mean measuring between ground and the other side of the resistors I marked? Seeing 0 V there is expected; pin 15 on the 3340 is a virtual ground, it’s held near 0 V by the internal summing opamp.
Still not sure why you weren’t hearing anything with 7.5 V in, since that should give you quite a bit more than 0.5 Hz (7-8 octaves more, even). What voltages are you seeing on the two resistors with the keyboard plugged in and playing e.g. A4 (440 Hz)?
Oh shit 
To be able to test this I connect the MOD output of my keyboard to the CV input of the VCO.
By reconnecting everything to measure the tension I have nothing …
I tell myself that it is the VCO which is bugging but I still test the MOD output of the keyboard and there I get no voltage … 
normalement tu devrais avoir du son sans CV externe.
as tu essayé de tourner le trimmer potentiomètre ?
tu utilise bien une alimentation symétrique (+12V/-12V) pour alimenter le VCO ?
normally you should have sound even without an external CV.
have you tried to turn the trimmer potentiometer?
do you use a symetric power supply (+ 12V / -12V) to power the VCO?
No it has no effect turning the potentiometers, I always have an oscillation every 2 seconds.For power supply it is that of a computer with + 12v / -12v / GND output.
je te parle du Trimmer (trim pot), pas des potentiomètres
si c’est un multi tours (ou pas d’ailleurs) que tu as utilisé, le faite que la fréquence de l’oscillation soit très très lente cela peut venir peut être de son réglage
traduction :
I’m talking to you about the trimmer, not the potentiometers
if it is a multi turns (or not for that matter) that you used, the fact that the frequency of the oscillation is very very slow it can come can be its adjustment
The resistance between pin 1 and 3, ie trimmer + 24k, should be roughly 30k. I’ve updated the drawing above to show that, plus I added a few more voltage test points.
But 0.5 Hz is close enough to “no CV at all” that I’d keep looking at that, until I’ve triple checked everything. The voltages at the points I marked, 100k paths from these points to pin 15, the main capacitor (marked CAP in the drawing), …
Oh ok sorry I didn’t understand 
. I tested and it doesn’t change anything either (my trimmer is a multi turn).
I test all of this and I tell you…
Thank you very much for spending time finding solutions !!! 
Oh, there’s definitely some oddities here.
- Between GND and pin 16 I have 5v.
– this should be 12 V. - Between GND and pin 3 I have -7.2v
– this is good!
- This most likely means that you have a working −12 V. The 3340 cannot handle that directly, so it’s connected via a current-limiting resistor and the −7.2 V is generated by an internal zener diode.
- Between GND and the two points of A or B I have 1.3v.
- I was a bit unclear here – there are two points under each letter, and you need to measure the voltages at both points (either at A or B) and add them together. Is that what you did? (come to think of it, 1.3 V might not be that surprising, given that pin 16 is 5 V).
- Between 3 and 2 I have 17.4M ohm – that’s a *lot* more than expected.
- And between 3 and 1 I am nothing at all.
- These are very wrong, but just checking: did you measure these with the power turned off? If not, your multimeter might be confused by the currents in the circuit.
I’d start by figuring out why you see 5 V at pin 16. That could explain a few things…
hi Fredrik!
the power off test gives me this:
-Between 3 and 2 I have 5.6k ohm
Between 3 and 1 I have 25k ohm
Now i have some change …
- My oscillator oscillates rather well without any CV input but only at the output of the square wave.
-Even if I have a square wave I still cannot change the frequency.
-I don’t know why it changes but it no longer works with my keyboard …
-I want to prescribe that his changes are not voluntary … I do not know what they are related to but that to change after my measurements.