Musical Modulator Circuit

Fill this circuit a simple audio tone, and it provides you back a musical note with a selectable drive, sustain and decay. Input impedance is 10,000 ohms, output impedance 1000 ohms, and gain is accord. Best results will be taken with signal inputs having amplitudes of 1 Volts peak-to-peak or less.

Musical modulator circuit part list:

R1 = 8K2
R2, R3, R4 = 1KΩ
R5 = 2M2
R6 = 15KΩ
R7 = 1MΩ trimmer potentiometer
R8, R9 = 5K6
R10, R11 = 250KΩ Linear taper potentiometer

S1 = normally open SPST pushbutton switch

C1 = 0.33μF/35V mylar capacitor
C2, C3 = 0.1μF/35V ceramic disc capacitor
C4 = 0.005μF/35V mylar capacitor
C5 = 2.2μF/16V electrolytic capacitor

D1, D2 = 1N914
IC1 = RCA CA3080 transconductance amp
Q1 = 2N3904 transistor
J1, J2 = phono jack

When S1 is pressed, the output volume increases at a rate defined by attack control R11. As long as S1 is pressed, the sound will be maintained. Delivering S1 causes the note to decay at a rate restricted by decay control R10.

Try sine, square or triangular wave inputs for musical representations. Among a noise input, you can simulate such things as gunshots and explosions. Trimmer R7 resistor can be customized to remove out all audible “thumping” (noticeable with a very fast attack or failure).