As I understand it, it's actually the torsion of the spring that transmits the signal. If the input and output aren't marked, the input coil typically has much

As I understand it, it's actually the torsion of the spring that transmits the signal. If the input and output aren't marked, the input coil typically has much lower impedance. Note: This is from repairing guitar amps when I was a teenager. The reverb unit had to be rugged and portable, probably dictating some aspects of the design.