VCO 3340 Sine wave

I made a new VCO with an AS3340, and i tested to add this circuit for a Sine wave out

(sinshapr = Triangle output)

Everything work, but the Sine is very low
already the Triangle is lower than Saw and Square, but here the Sine is even lower than the Triangle.

Someone could tell me if it is possible to increase its output volume by changing some component of the schem please



Badass! you could also figure out a way to boost the triangle and you would see some benefit at the sine

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thx but the pin 10 (triangle) of 3340 go directely in the opamp without other components, i don’t see how to increase it, i was thinking that it be more possible with the Sine circuit with some resistor

Can i remove the 33k between pin 13 and 14 of opamp ?

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What does the rv10 do here? Shaping?

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technically I don’t know


When in doubt? Whip it out!
See what happens without?
There are a few triangle to sine methods none are lossless (maths is a bugger). Experiment. Lots. And when you’ve got it sorted tell me as I’m just about to do the same addition to a 3340 too.


yes i have already tried to adjust the 2 trimpot, but no change regarding the output volume

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Where’s this circuit from? Is there an explanation of it?

In particular I’m trying to figure out what the op amp is doing.


Adjust or remove completely? Try taking rv9 out too.
The main problem seems to be the low triangle output from the 3340. Try another triangle source. Your circuit may not be the issue at all.

Can I just add it took me an age to work out the circuit is right to left. Amazing how something that trivial can throw you.

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here’s the complet schem

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RV9 is adjusting the current flow into the shaping circuit. No point in taking it out as a test, if you run it all the way up (or down, whatever) it’s 0 resistance. And one would think that’d make the level louder. nope


Where’s it from? Any explanation of how it works?

no sorry it’s just a schem that I have in my files without knowing where I could find it at the time,
but quite similar to the others schem with a CEM3340 or AS3340

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Are you taking the input directly from the 3340 pin or after the buffer. I found an interesting stripboard sine add on for the 3340 on electromusic I was about to try. (Sorry, I’ll add a link tomorrow)

It’s similar to the sine shaping in the Thomas Henry VCO Maximus, but some components are different:


(and he uses ±15V). Unfortunately not much explanation, and it’s claimed to give a large signal:


The sinewave is created by overdriving the differential pair Q1/Q2 with the triangle wave (cool mathematics there!). Trimmer R41 sets the symmetry, while R40 deals with the roundedness. The best way to tweak these is by ear: while listening, adjust them for minimal harmonics. It is often the case that what you think might be the best setting by eyeball on a scope in fact falls short of what the ears can detect. In any event, you can expect a very satisfactory sinewave from this proven topology.

Sine Wave

Figure 3: Sine Wave Output

As usual, the amplification is kept high so that it may be chopped down to a desired level by divider R9/R10. The resulting amplitude is 10Vpp with an output impedance of 1k, of course. See Figure 3.


That’s very similar to the stripboard design I’m using from the electromusic thread.

after the buffer

i have also post this in an other thread


This design comes from the pin.

VCO Maximus comes from the buffer


I notice the Maximus’s R11 and R12 (refs from your diagram) are considerably larger than in your diagram (2.2k vs 470R), and R31 is much smaller (18k vs 68k). R30 and R36 are somewhat smaller (20k vs 33k). R39 is larger (390R vs 220R). I have no idea what changing any of them would do but it might be worth trying. By the symmetry of the circuit I think R37 and R38 are supposed to be equal, and R31 and R32 too. I’m less sure about R30 and R36.