How to make a Voltage Controlled Oscillator

The 74HC4046 has problems when the control voltage is low. Many people find they can't get better than a 10:1 ratio.

Use a 4000 series 4046 instead, they work over a 1000:1 range.

Clifford Heath.

Square wave or sawtooth is fine. This is for a chiptune synthesizer.

Depends on use. Too large a tuning range makes for a noisy, cantankerous-to-control, oscillator.

You _could_ roll your own using a package of LM339's ...Jim Thompson

Two components plus a high voltage power supply and shielding :)

A 555, diddle the voltage on pin 5 (threshold?).

Wow this one is pretty easy. I'm going to breadboard it to see what kind of output I can get from it. Hope I still have those 74 series chips.

Tuning range? (fmin...fmax) ...Jim Thompson

-- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at

I can see November from my house :-)

On a sunny day (Tue, 26 Oct 2010 11:18:57 -0500) it happened Vladimir Vassilevsky wrote in :

That is only a very short time of experience really.

I dunno, I am in the Netherlands.

Here's a simple 1 volt/octave audio VCO:

For best results, transistors Q1 to Q5 should be in thermal contact. R4 can be made a trimmer pot to get an exactly 1 V/octave response. R1 can be a resistor with a temperature coefficient of -0.33%/degree C and also put in thermal contact with the transistors to partly cancel the VT temperature dependence of the differential pair.

oops, picture came out too small! Try zooming in on this link:

About hearing range. 30hz - 16khz would do.

This one seems to require a password.

Does it work that way? I remember having to change a resistor value to change the frequency. I remember threshold pin as used for PWM. I maybe wrong though. It was a long time ago.

One more time. The site was resizing images as its new default setting. Sorry!

If you're building a music synthesizer, then many of these simple VCO suggestions may not work for you, because the relationship between the control voltage and the output frequency is some nonlinear function - though if one had something like an exponential frequency response it might be possible to use a microcontroller with a look up table to get the appropriate pitches.

Also you have to consider the temperature stability of the oscillator, the ear is VERY sensitive to even small pitch deviations.

Cem Uzunoglu:

You can't hear notes that high. 66 Hz - 5 kHz will do.

Vladimir Vassilevsky:

ROTFL. Well, maybe the last two...

By all means.

Thyratron has variable breakdown (when grid is biased to the "linear" region), but it's just as noisy as the neon. They make bad sweeps, but they're easy to synchronize thanks to the gain.

They do tend to discharge the capacitor more completely, for a wider range of capacitances. Neons tend to turn off in the 20-60V range, lower for bigger C (~1uF makes bright blue-orange flashes :) ).

How do you "latch it into the open state"?

Tim

Current Mirroring _way_ more complicated than need be ;-) ...Jim Thompson