cheap crystal filter

A novel approach is employed in this circuit, which allows mixing of two audio signals and cross-fading between them In view of the dramatic drop in the price of crystals used in colour TV sets, they now represent an . economical way of building an SSB-filter. The circuit shown in the accompanying diagram is for a filter with a -6 dB bandwidth of roughly 2.2 kHz.. Rather than using conventional potentiometers as analogue attenuators together with a summing amplifier, the circuit functions by sampling the two signals alternately at a high frequency.