Hi All,
I have made this circuit, it is a voltage controlled amplifier.
The signal in works but the voltage control (CV) doesn't. What is the best way of finding my error?
I have checked the resistor values. All the connections and changed all the active components so far.

 

The signal in works but the voltage control (CV) doesn't. What is the best way of finding my error?

What is the circuit doing?

Start by checking the biasing of U1C. Do both CV inputs not work?

 

http://www.musicfromouterspace.com/analogsynth_new/DUALVCA/DLLVCA001.html
It's this circuit. All the cv's don't work, but if I turn the volume right up I can just hear it.

 

All the cv's don't work, but if I turn the volume right up I can just hear it.

Does the log/linear switch make a difference? Have you checked DC biasing for U1C?

 

Does the log/linear switch make a difference? Have you checked DC biasing for U1C?

The switch makes no difference, and yes I put the trimmer to 0 volts. I've been looking at this circuit for about six hours!

 

The switch makes no difference, and yes I put the trimmer to 0 volts. I've been looking at this circuit for about six hours!

U1C is common for the log and linear switch setting, so make sure it's working. Check the DC biasing.

 

http://www.musicfromouterspace.com/analogsynth_new/DUALVCA/DLLVCA001.html
It's this circuit. All the cv's don't work, but if I turn the volume right up I can just hear it.

What do you mean, "I can just hear it". are you connected directly to a headphone / speaker or are you sending the signal through an amplifier?

Also, turn your Bias Adjust up so it is at 1.2 to 1.4V (or more).

 

What do you mean, "I can just hear it". are you connected directly to a headphone / speaker or are you sending the signal through an amplifier?

Also, turn your Bias Adjust up so it is at 1.2 to 1.4V (or more).

There is an oscillator connected to the CV when I turn it up in frequency I can just hear it. The circuit is connected to a hifi.

 

One thing I should of said was that the q4 transistor was around the wrong way when I first turned it on resulting in the 2n3906 transistor burning out. I then corrected this and replaced all the active components on the circuit. Could this have effected any of my passive components?

 

Lift pin 1 of the OTA (U2-A). Connect a 25K resistor between pin 1 and +V. The amplifier will then be at full gain so you can check it out.

 

Measure the voltage at Vout when it is connected to your HiFi. The input impedance of your HiFi may be too low and attenuating the signal of the VCA. If so, you'll need a buffer (pre-amp) between your VCA and HiFi.

Also, BiasA POT should be adjusted to have 0V at Vout with no signal.

Are there people on the webs who have had success with this circuit, or has it garnered little enthusiasm because it doesn't work?

 

Im going to put this into practice when I get in the studio tomorrow morning, thanks for the advice!

 

Im going to put this into practice when I get in the studio tomorrow morning, thanks for the advice!

I got it working at last, I put a positive instead of negative into an IC:-( sorry for my stupidity.