A few, perhaps unusual, Univibe questions...

[Isaiah]

Hi all...


http://www.lynx.bc.ca/~jc/UnivibeManual3.gif

In each filter stage, one of the phase-splitter output caps is different to the last.
I believe they are 15nF, 0.22uF, 47-something and 4.7nF.
I know these are part of the Univibe 'sound', as there are mods for other phase-shifters to create
more Univibe-like.
What if said capacitors are all the same value? will this make the Univibe sound more phaser-like?



Would it be possible to convert the filter stages from all-pass to low-pass?
I imagine this would involve adding a cap to ground somewhere in the RC networks of the filter stages,
but I'm not sure where.

Drifting off to sleep at stupid o'clock this morning, I thought about this -
http://mypeoplepc.com/members/scottnoanh/sitebuildercontent/sitebuilderfiles/mutant_filter.pdf
On page 5 there's a low-pass filter based on a Buchla design.

Here's my idea - the RC network between U1A and U1B (C2, C3 and VT1. I imagine C1 and R16 could be omitted) is 'reversed' so that instead of there being one input into the RC network and two outputs into a differencing op-amp,
there are two inputs (fed from each side of the Univibe phase-splitter) into the RC network and one output (into the next Univibe filter stage).
Could that actually work, or am I setting myself up for some heartache?

Thanks in advance!
I really appreciate all the help I've been given recently.

Alex

[John Lyons]

Alex

From what I've read you can make the caps all the same and it will sound more like a phaser...well, actually it will be a phase pedal then...

Not sure about the other questions... Bump!

John

[Isaiah]

Thanks, John.
I thought that might be the case.
If I do manage to modify this to get low-pass response, I think I'll stick with the same cap values for each stage.


So... Low-pass response?
Bump!

[Isaiah]

So...
I've breadboarded 2 stages, each one manually controlled by a pot (I don't have the necessary LDRs or a dual-gang pot at the moment).

A few notes -
I'm powering it all with a 9V battery.
I omitted the pre-amp section and just started with on of the phase splitter stages.
At the moment, I'm using 0.1uF caps on both outputs (Collector and Emitter) of each phase splitter.

The phasing effect is pretty mild (I guess it's more noticeable when swept by an LFO) -
It's certainly no Small Stone in the configuration I have it in, but I think it'd be useful as some sort of
utility filter. I'm sure it'd sound great before or after a heavy-clipping circuit for a PWM-like effect.
After some experimentation, I'll probably build one as I described above, perhaps with a Resonance control.

The phase-splitter stages sound great when used just as a buffer (without the RC network on the output).
I guess that's due to the high impedance, right?



I'm still not sure how to go about achieving a low-pass response from the all-pass RC network.
Any help, please?

Thanks,
Alex