Vibrato Question

[Christoper]

What are the traditional ways of controlling the speed of a vibrato pedal? Are there many different ways of doing it, or are they all just variations of the same idea. The only three notable designs I know of are the Boss VB-2, Diamond Vibrato, and the EHX Pulsar.

I don't need to know the nitty gritty of how these things work, just a block diagram level of detail.

Moving forward I would like to try to design my own vibrato circuit, but for now I'm poking around in a Marshall Vibratrem and a Berhringer UV300 (based on VB-2)

[antonis]

It clearly depends on which configuration is utilized for LFO..
e.g. phase-shift, twin-T, Wien-bridge, etc..
I presume with "speed" you actually mean "frequency" so it's more easy to make the "R" part of RC time constant variable..

P.S.
The vast majority of "vibratos" are in fact tremolos..
i.e. pitch modulation (doppler effect) vs amplitude modulation..

[ElectricDruid]

From a quick hunt around online for schematics (I notice you didn't provide any, Christopher... ) it looks like the Boss and the Dimond pedal are vibratos, but the EHX is a tremolo. So that one does something different for starters - that's a volume variation, not a pitch variation.

The important thing would be to make sure that the LFO linearly modulates the BBD clock *period* not the frequency. This is because the overall delay is the sum of the last X clock periods, where X is the number of stages in the delay line. The delay is proprtional to 1/f, not f, so modulating the period not the frequency gives a much better result. This comes through as much less distortion of the LFO waveform, so your "sinewave" LFO actually produces something much closer to a sinewave pitch shift. It's still not exact because the delay time is actually an integration over time of the clock period curve, but it's getting pretty close and for short delays and slow LFOs it's close enough. All decent analog BBD vibratos and chorus pedals work this way by now, even if they're just blatant clones and don't understand why and just copied some already-successful design.

HTH

[Christoper]

From a quick hunt around online for schematics (I notice you didn't provide any, Christopher... ) it looks like the Boos and the Dimond pedal are vibratos, but the EHX is a tremolo. So that one does something different for starters - that's a volume variation, not a pitch variation.

Oh yeah, I didn't mean Pulsar, I just also happened to be looking at a good deal on one and got my signals crossed 

I do have the schematics for one design in question, but it's not publicly available, so we'd have to DM about it if you want to talk