Audio Modulator Noise

As Dave says, we NEED to see a circuit diagram.

If you have something there that you're experimenting with, we need the circuit diagram or "schematic diagram" of it, and the modifications you've been making to it.

If you can't trace out the circuit of the existing pedal, you can at least draw up a diagram of the bits you're trying to add to it.

You can also post photographs of the existing pedal, and your new circuitry, and how they fit together. A picture is worth a thousand words and will often enable us to recognise a problem that's obvious to us but not to you. So it's nearly always worthwhile to take some pictures and post them here.

 

Does this click happen once in every cycle of the sinewave generator? Does it always happen at a particular point in the cycle? If so, which part?

Have you looked at the LED? Does it increase and decrease smoothly in brightness? Set the modulation oscillator to a very slow frequency and watch the LED carefully.

You said the modulation oscillator is powered from a separate isolated supply. Have you used batteries, with no connection at all to any of the other circuitry?

Have you disconnected the original gain potentiometer in the stomp box? Were only two terminals of that potentiometer used, or were all three terminals used? What is the resistance value marked on the potentiometer? What is the type number of the LDR?

Can you take a photo of your whole setup and post it here?

 

I dont understand what you are doing and what you want to accomplish.
But a wild guess: Your photoresistor is picking up light from the LED as a train of pulses and sending it to the signal path which results in a repeating clicking noise. If the clicking is at the same frequency as your generator, then this is probably the problem..

 

Easy. Just made this up for ya:
http://img189.imageshack.us/img189/7874/386amp.png
It's a standard variable-gain LM386 amplifier, but uses a FET to induce voltage control to the gain control resistor, thus causing fluctuating gain. Input your sine wave, and you should be good to go.

This is more designed as a standalone unit. To control an existing pedal, simply use the resistor+FET scenario with the gain pot.

 

Perhaps you would save the attitude until after you've responded to all the questions I asked you in my previous post on this thread?

 

Okay, I see what you are trying to do. The problem is that the LED only conducts in one direction, so, fed with a sine wave, it is off 1/2 the time (actually more than that because it needs about 2V before it conducts). The on off threshold is the click you are hearing.

Does the fucntion generator have a DC offset function? If so, you should turn it up to the point where the LED never goes fully off. Otherwise you would wire the LED with two resitors, one going to the signal generator and the other to a battery to provide DC offset.

Bob

 

He said he had an OpAmp-based sine wave generator in post #1

However, cloudy, I'm glad the idea worked for you, but these are nice people and just want to help. I'd recommend taking Kris's advice. I learned that the hard way.

Good advice Bob! I continually forget about my diode's voltage thresholds and it creates a lot of problems, especially when building guitar circuits.