Etherwave phones circuit

I was wondering how to add a headphones volume control knob to my self build etherwave? In the hot-rodding guide (p12.) I can find a circuit build around a TL081 opamp, but it has no pot attached.

How do they do this in the etherwave plus? Are there any etherwave plus circuits available on the web?

The Etherwave plus circuit is just a combination of the circuit parts which had first been published in the hotrod manual. Things like adding a volume pot seem to have been too trivial to publish them. It's a 50k log pot which has its outer pins at the original audio output and ground while the wiper pin goes to the TL082 circuit.

thank you. that's the answer i was looking for.

Thierry can you tell me wat the foil in these cabinets is for? Is it connected to the gnd signal? is it important to do this in a home made theremin?

This foil is connected to ground. It forms a variable capacitor together with the antenna wire which passes above. Bending this wire closer or more far away from the foil allows to fine-tune somewhat the linearity in the highest register. 

When you build the original EM circuit with 4 x 10mH linearization coils, there is no need to put it, it won't change a lot. But if you go for the more modern variant with 3 X 10mH, you should put it, simply because this small amount of additional capacitance will make the antenna circuit more stable.