UNIVIBE

[zolee]

Hi,

 I built a univibe recently. The problem with it is that when slow, the effect is far from a sinus wave. It's rather fast cuts taking place far from one another in time, if you know what I mean. Might that be the transistors in the LFO?

[lightningfingers]

you built a univibe :shock:  :shock:  :shock:

sorry i cant help but thats pretty impressive

[Mark Hammer]

The problem is with the symmetry of the LFO waveform, or rather, what the LFO waveform does to the LDRs.

Some LDRs go low in resistance faster than they go high.  If you are using a triangle-wave LFO to drive an FET that responds *immediately*, then you might not hear a problem.  But if the LDR changes at a different rate when the LFO goes up than when the LFO goes down, perhaps a triangle wave is not the best.

It seems to me, you may want to ask people how to change the symmetry of the LFO waveform so that it goes up differently than it goes down.  Maybe you need something that is a little more like a ramp than a triangle.

[Eb7+9]

... when slow, the effect is far from a sinus wave

Have you noticed, at this slowest speed setting, if the bulb shuts off completely during the LFO cycle ??  If it does then that would explain it - a typical problem with the Vibe ...

Like Mark mentioned, a good chunk of the UNIVIBE action occurs just before the bulb stops burning - conversely, this explains why you don't get that much more filter effect by making the bulb glow really bright at the apogee of the LFO swing ...

At the slowest speed the LFO amplitude is reduced so that, normally, you'd have the intensity cranked up all the way to get the most effect, which would be sinusoidal in nature following proper adjustment ... if you've made the bulb driver adjustable as per my mods then you can set the gain and bias of the driver circuit so that the bulb comes barely close to shutting off at min LFO speed and max intensity setting ...

If you haven't made the bulb driver circuit "offset" adjustable and only have the stock "gain" trimmer then you'll have to put your hands on a bulb that lights up with less current ... changing the LFO transistors won't change much since the LFO and Bulb Driver circuits are AC coupled and here we're dealing with a DC offset problem in the Bulb Driver circuit ...

... jc

[zolee]

thanks Eb7+9,

I will certainly try your mods. Until then, I adjusted the lamp so it's very close to a sinus wave right now. The effect got deeper, too. It was just too bright, I believe.