Something may be too close to the volume antenna. Make sure the theremin is set up on a mic stand (not on a table). Make sure that no cables are near the volume antenna. Any object near the volume antenna will reduce or shut off the volume.

Check your amplifier and audio cables with another instrument. Check the power adapter with a voltmeter: set the meter to measure AC volts. Measure across the two outside pins of the adapter (at 9:00 o’clock and 3:00 o’clock).

You should get a reading of 14 to 16 volts. If your adapter is working, but you still have no volume, see Tuning the Volume Circuit.