If you want a simple Wah circuit, spend out for a 500mH choke, and build a Cry Baby (or one of its variants) but be sure to add input and output buffering. I gave up trying to use this type of filter a long time ago - if you get a sufficiently high Q for a reasonable sound, you run the risk of self-oscillation (especially with an unbuffered filter output), and if the Q is lower it just sounds like an ineffective treble tone control. It won't sound anything like a conventional inductor-based Wah - it's a twin-T filter and these have a very different response shape anyway. You might get lucky and get a reasonable range of sweep out of the filter, but the values are wrong for a good Wah sound. It's a simple method, and gives a good range of resistance change, but requires a bit of mechanical work if you're going to replicate it. Morley use fixed illumination and a shutter attached to the pedal that interrupts the light path. The final obvious problem is that if you're trying to use ambient light with the thing, it's going to be affected by shadows, it will hum at mains frequency because of the "flicker" of mains driven lighting, and will be useless on stage with people moving about, lighting changing and so on. The next problem is that the conversion from LED current to amount of light is in no way linear, and below a certain point LEDs emit no light at all - the "curve" of the frequency sweep will be very non-linear. One of the problems is that it's going to draw quite a lot of current because you're running those LEDs all the time. It's really not a very good circuit - you can see that it's based on the Morley optically controlled Wah Pedals, but the values have been tweaked. It works best when illuminated by plenty of natural ambient daylight, so I'm afraid it is not particularly suited to darkened stages! Now as you lift your foot/rock backwards on your heel to expose the LDR to ambient light, the wah sound should become more dull just like a real wah. The other LED serves as a visual indicator to set the sensitivity Cover the controller LDR completely, and adjust the sensitivity until the LED is just lit, and the trebly-ness of the "wah full forward" is to your satisfaction. Exactly how bright it goes (and therefore how trebly the wah effect) will depend on the sensitivity setting. The shrink-wrapped LED illuminates the LDR between the caps and makes the sound brighter. If you use the LDR that's connected to the transistor as the wah "foot controller", and shrink tube the LDR between the caps and one of the LEDs, covering the "controller" LDR makes both LEDS glow brighter. Hakanenlauri wrote:The sound becomes brighter when the ldris covered and muddier when there's light.
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