Duo-Phase Mutron LED+LDR principle ?

[Dali]

This is not about building but more about the sorcery behind the Duo-Phase.

Do I understand that the LEd will blink and sensors (LDR?) will catch the variation and "do something"?

I was not able to find a video demonstration of the LEDs/LDR and the influence on the sound.

I'm just curious.

 

[Nostradoomus]

It’s a variable resistor that varies based on the light intensity that is cast on it. I think the most simple way to think about it is like a potentiometer...no light = pot all the way to the left, full light = pot all the way to the right. Everything in between depends on the intensity of the light from the LED.

 

[Dali]

Thanks for taking time to answer @Nostradoomus !

Everything in between depends on the intensity of the light from the LED.

And then, what makes the LED change intensity? Is it something pulsating or the actual guitar notes/sound input?

 

[phi1]

The led pulses come from the LFO circuit (made up of op amps IC6A.1, IC6A.2 and IC5A.1 and surrounding components). So the led blinks at the set rate regardless of the guitar input. You can see this portion of the circuit is separate from the guitar input.


This is the same theory behind many phase, vibe, tremolo, and modulated delay pedals.

There are many compressor designs which also use an led/ldr. In these designs your guitar input lights the led, and the increased resistance of the ldr is used to reduce the volume.

 

[Dali]

Thanks @phi1 and Nostradoomus. Your answers are highly appreciated !