Ive been trying to get started on making a semi-modular synthesizer from scratch, So i got started by trying to make the VCO for the synth with some LM741 op amp ICs but the designs i tired ended up not working. I was wondering if there is a better op amp or other IC for making a VCO for audio applications. Thanks!

 

I assume you want a sinewave output?

 

I assume you want a sinewave output?

square wave and triangle wave outputs

 

square wave and triangle wave outputs

Simultaneously?

How much of a frequency change are you looking for versus voltage.

 

The easiest circuit is a square wave and an integrator, which turns the square wave into a triangle wave. The square wave can come from any source of VCO, but the integrator might give you issues as you increase frequency due to the fact that it will shrink with shorter square wave pulses. Another option is starting with a sawtooth - which is also fairly simple.
Actually making a VCO involves controlling an oscillator (relaxation osc, like 555 timer, or equiv.) with an input voltage. Having looked into the schematics of many old-school analog synthesizers, the paths vary, but most look like this: convert the voltage to a current, then use that current to determine the ramp of a capacitor-charge circuit. Capacitors charge linearly when charged by constant-current.
This will generate a sawtooth, which can be hooked up to a comparator for the square wave output. One trick that I rather liked involved making a triangle wave by using an amplifier that inverts, but gets saturated and follows the input when the input is too low. The result is a triangle, because the upper half of the sawtooth is inverted and the low half is the same.
The circuits for these are generally found when you search for "VCO schematic" and they usually include important pieces like compensation and proper biasing if you're using single-supply op amps. I suggest using a dual-supply for simplicity, if you have one. If you don't the circuit will be more complicated, but the power arrangement will be simpler; it's a personal choice.
Let me know if you need a more exact circuit idea for these or if you have enough to get going. One of the key parameters you'll need, though, is the dynamic range of the VCO, as others have noted. This takes a fair amount of research and calculation, so take your time and make sure you're happy. Most likely, people have already calculated everything and you can go off of theirs, such as ci139's post above, for an 88-key keyboard. The range of musical notes, number of keys, and power availability, will help determine the choice of dynamic range.
Sam Gallagher

 

Try the LM566 chip,,

https://www.google.co.uk/url?sa=t&s...ggbMAA&usg=AFQjCNEkXVnBJvJibeCf2vmsI9xTVAU_Lw

 

I would also recommend XR8038 or XR2206 if you can find a source.

For square wave generation, look at LM331.

 

The 8038 or 2206 are fine chips but Exar no longer makes them. The only sources I can find are on EBay, so the pedigree is suspect.

AFAIK these are linear controlled oscillators, and music is exponential. Decades back I played with one using a diode/op amp to get the exponential from a linear input. It almost worked, except any changes in temperature of the diode could be heard as a change in pitch. Not only the temperature of the room but the preceeding note and the duration of a note would change the pitch.

 

Hello,

Music from outer space has a VCO schematic:
http://www.musicfromouterspace.com/analogsynth_new/VCO20120618REV0/VCO20120618REV0.html

Bertus

 

square wave and triangle wave outputs

Well I found this...http://www.allaboutcircuits.com/projects/diy-synth-series-vco/

 

The 8038 or 2206 are fine chips but Exar no longer makes them. The only sources I can find are on EBay, so the pedigree is suspect.

I've got 8038 from both Intersil and Exar as well as Exar's 2206 from Ebay(China) and they all work. (never done any stress tests on them but...) I have a VCO/waveform/function generator IC addiction

(give me oscillation or give me death)

However. The thing that all of the Ic's that were manufactured to serve that purpose seems to be discontinued... It's understandable that modern synthesizers and function generators would require more stable, precise methods....For a hobbyist or a noob though...

But still...Not in great demand yet I ordered them.

 

I'd just throw a cpu at it and do it in software.

 

I'd just throw a cpu at it and do it in software.

My thought as well. But when you are battling the basics you want the raw deal. For further understanding.

I for one have used digital software for making music over 20 years. The reason I went into electronics was to understand it on the very fundamental hardware side of things that gets lost in the software side of things.