LDR controlled Inductorless Wah - noise on higher voltages

[nordine]

hi guys,

i've been wondering if this is an unsolvable problem -due to design-, or if there's any fix

i made a colorsound inductorless wah (you know the one transistor twin t circuit controled by resistance to ground), then put a LDR on the 100k pot, then, proceeded to 'stimulate' it with a LED

the problem is, when the LED gets really bright, there's a pop at the highest brightness (i'm controlling it with the vanishing point sequencer)...

at first i thought it would be something related to voltage shifts produced by the LED, but discarded that hipothesis, cause it 'pops' only when the LED is facing the LDR ..now, if i dim the highest bright, i don't get 0 resistance -or maximum treble sweep of the wah- which is frustrating

any hints?

[nordine]

anyone?

[d95err]

I don't really know what that sequencer does, but perhaps the problem is with the power supply. A wild theory: The LED will draw lots of current at maximum brightness and perhaps that's causing secondary problems with the audio circuit.

As a test, try temporarily powering the LED from a separate battery and see if the problem goes away.

[nordine]

i also thought that at first, but the thing is, it doesn't do the 'pop' when you cover the led and isolate the LDR from it's light...

it's like the sudden LDR resistance changes affect/distort the transistor... but i can't see how it's happening, neither how to fix it 

[R.G.]

I would measure to see if there is DC across the LDR.

[mac]

Did you put the 100nf to DC-isolate both 180k in the feedback loop?

mac