This is the schematic of the Mixer

Part
Total Qty.
Description
Substitutions
R1, R3 2 10K Pot
R2, R4 2 100K 1/4 W Resistor
R5 1 6.8K 1/4 W Resistor
C1, C2, C3 3 0.1uF Capacitor
Q1 1 2N3819 Junction FET
MISC 1 Wire, Shielded (Metal) Case, Phono Or Other Plug For Output