Vco needs driver?

[Jos]

You might want to read this:

Advice for troubleshooting 3340 based VCO

This is a wiki post; please correct and improve! This is written regarding the 1222 Performance Oscillator module, but similar things apply to the simple stripboard oscillator or other oscillators based on the 3340 chip. For the stripboard version also see If you are not getting good tones from the oscillator, do the following. If with the 1222 you are also not getting good behavior from the tuner, don’t waste time on trying to fix that yet. Get good tones on the outputs first — the tuner won…

@hansun

First just a speaker, then an amplifier before speakers

A vco is not meant to be connected to a speaker directly. Depending on the impedance of the speaker you may hear something if that impedance is high, but that is not the case with modern speakers. You may need to set a frequency and get the VCO to trigger. But most likely it is free running, so it should always produce some signal.