MFOS Guitar or Audio Signal to Gate and Gained Up Output

Ray Wilson authored this content while he was actively running MFOS as the founder and resident genius.
We retain the content because it reflects a valuable point of view representing that time and place.

Article by Ray Wilson

Guitar to Gate

This is a decent guitar to gate circuit. It sustains well on most notes. It takes you guitars signal and applies a gain of 100 to it then full wave rectifies it dropping the rectified signal on C3 charging it rapidly. When the guitar note dies the cap discharges via R13. U1-C is a comparator which goes high when the guitar's strings are played in response to the charge on C3. R7 and R8 set the threshold voltage for comparator U1-C. LED1 illuminates when the gate output is high. U1-D is used to provide some gain to the instrument applied to the input so that it will be high enough in amplitude to put through your VCF, VCA, etc. You could build this circuit on a small breadboard or stripboard.

 

Guitar to Gate Project Parts List

Qty. Description Value Designators
1  LM324 Quad Low Power Op Amp  LM324  U1  
2  Diode 1N914  1N914  D1, D2  
1  LED  LED  LED1  
2  Potentiometer  100K  R2, R14  
2  Resistor 1/4 Watt 5%  100K  R5, R8  
5  Resistor 1/4 Watt 5%  10K  R3, R10, R12, R17, R18  
3  Resistor 1/4 Watt 5%  1M  R6, R13, R16  
1  Resistor 1/4 Watt 5%  3.9K  R9  
1  Resistor 1/4 Watt 5%  4.7M  R1  
2  Resistor 1/4 Watt 5%  470K  R4, R11  
1  Resistor 1/4 Watt 5%  47K  R15  
1  Resistor 1/4 Watt 5%  82K  R7  
1  Capacitor Alum. Nonpolarized  10uF  C5  
2  Capacitor Alum. Nonpolarized  1uF  C1, C4  
1  Capacitor Ceramic  .01uF  C3  
2  Capacitor Ceramic  22pF  C2, C6  
1  Capacitor Electrolytic  100uF  C8  
1  Capacitor Electrolytic  470uF  C7  
3  Jack 1/4" 2 Terminal    J1, J2, J3