True pitch vibratos

[Marc.yo]

Are there any true pitch vibratos out there? I mean ones that actually alter the pitch. Not just act as a tremelo.

thanks

[Rodgre]

Search for info on the Boss VB-2 Vibrato. BYOC has a kit for it, and Behringer will soon have a $40 clone of it.

Also search for chorus/flanger projects that let you kill the dry signal.

Roger

[markm]

Seems there has been alot of work being done on a Brownface Vibrato as well. 

[Joe Kramer]

Or you could get hold of a Boss CE-3 for cheap and do this mod:

http://www.diystompboxes.com/smfforum/index.php?topic=57655.0

[Mark Hammer]

You can do it with just about any phaser, flanger or chorus.  Unfortunately, most commercial phasers, flangers and chorus pedals use a single FET to "bypass" the effect by cancelling the wet signal. This creates a logistical problem.  Since getting the pitch vibrato involves lifting the dry signal while the wet signal is on, you can't simply switch the effect in and out with the existing electronic switching.  the "bypass" mode will simply end up being silent.

There IS a solution, though.  The flip-flop circuit only uses one of its two outputs to engage the single FET.  If you interrupt the dry path to the mixer stage and insert a SPST toggle in parallel with a second FET, and connect that FET to the other side of the flip-flop, the pedal will always make the connection for the dry path when in bypass mode, and you'll be able to have the dry path either on or off when in effect mode.

[Marc.yo]

You can do it with just about any phaser, flanger or chorus.  Unfortunately, most commercial phasers, flangers and chorus pedals use a single FET to "bypass" the effect by cancelling the wet signal. This creates a logistical problem.  Since getting the pitch vibrato involves lifting the dry signal while the wet signal is on, you can't simply switch the effect in and out with the existing electronic switching.  the "bypass" mode will simply end up being silent.

There IS a solution, though.  The flip-flop circuit only uses one of its two outputs to engage the single FET.  If you interrupt the dry path to the mixer stage and insert a SPST toggle in parallel with a second FET, and connect that FET to the other side of the flip-flop, the pedal will always make the connection for the dry path when in bypass mode, and you'll be able to have the dry path either on or off when in effect mode.

Thanks for the info

[Processaurus]

I killed the dry signal from my small stone clone to get only the pitch bent sound, and patched in a EA tremolo type phase shift LFO before the depth pot, it sounded decent, much better than the stock triangle LFO when it came to making a natural sounding vibrato without abrupt changes in pitch.

[Joe Kramer]

I killed the dry signal from my small stone clone to get only the pitch bent sound, and patched in a EA tremolo type phase shift LFO before the depth pot, it sounded decent, much better than the stock triangle LFO when it came to making a natural sounding vibrato without abrupt changes in pitch.

That's the bigger problem with the just-kill-the-dry-signal attempt at vibrato.  Since most choruses tend to use a triangle wave, you get pitch bend that doesn't have a whole lot of musicality (IMHO).  That's why the Boss VB-2 uses a sine LFO and that's why a stock CE-3, with it's wet output already provided, doesn't automatically double as a poor man's VB-2 without some tweaking.

BTW, this mod would probably work for most triangle wave LFOs:

http://www.diystompboxes.com/smfforum/index.php?topic=57655.0

[Mark Hammer]

This circuit is intended to provide "hypertriangular" sweep for phasers, flangers and such, and might provide a useful mod for the standard triangle generator (which you can see is part of the circuit): http://hammer.ampage.org/files/hypertriangleclock.gif

As it notes, it is an adaptation of an earlier circuit that also appeared in POLYPHONY.  The critical part if the interesting use of the diode with the 2N3819 FET.  The original used a diode on each side of the gate (gate-to-drain and gate-to-source), then full-wave rectified the result to get a sine wave at one end of the sweep and triangle-like wave at the other end.  That ended up being more complicated than needed.  This clever use of a single diode allows the same result to be achieved without requiring the rectifier.

[Joe Kramer]

Hey Mark,

That is a VERY cool circuit, and thanks for making available to the world.   

A while back, I spent several days tweaking with it to try and get it to work in a single-supply app.  The only way it would work for me was with large coupling caps on input and output.  That was no good, since the waveshape degraded at slower LFO speeds.  Next, I tried a nine-volt split-supply (+/- 4.5V), and that tended to pull the supply voltages off-center unless I used a buffered virtual ground.  The whole thing started to grow more parts than the rest of the circuit it was supposed to drive!  That's when I reverted back to experiments with diode clippers, which work plenty adequately for LFOs, IMO.

As for the hyper-tri trick, I'm a true believer, though I do it using the simpler diode-clipping method.  It's sounds wonderful in my phaser, and I've also rigged it into my univibe knock-off.  If you're a univibe fan, you owe it to yourself to try it there.  The tone of the vibrato setting is much less warpy, much more even throughout the sweep.  Of course you have to backtrack a bit and start with a triangle wave, which is not standard for most univibe circuits. . . .

   

[lowstar]

the bad stone has a switch to set it to pitch vibrate.
see topopiccione for the files.
it is a very cool phaser by the way 

cheers,
lowstar

[Mark Hammer]

Here's the hypertriangular circuit in action in the Thomas Henry Smoothphaser that was in Electronic Musician in June 1988.  You will note that it permits vibrato simply by panning the blend control in the appropriate direction.  Though it varies from unit to unit, I suppose, turning up the regen/feedback in vibrato mode tends to produce a more filter-like sound.:

I try not to post this one because it's such a tease. I hate showing people stuff that they can't get the chips for anymore (the SSM2040 in particular).  Seems unnecessarily cruel.   Though in theory you could replace the entire SSM2040 assembly and those 4 allpass stages with one of the Tonepad Ropez expander modules.  It's just 4 OTA-based allpass stages.

[Joe Kramer]

Bam--there it is.  Thanks Mark, I've never see that TH schemo before.

The LFO looks like the basic Schmitt trigger/integrator set-up, similar to the Boss-style triangle LFO that I borrow for most of my modulation needs.  Can't beat it for single-supply and low parts count.  If my hypertri univibe knock-off is any gauge, I'll bet the vibrato sound of that TH circuit is really nice. . . .

[Processaurus]

I killed the dry signal from my small stone clone to get only the pitch bent sound, and patched in a EA tremolo type phase shift LFO before the depth pot, it sounded decent, much better than the stock triangle LFO when it came to making a natural sounding vibrato without abrupt changes in pitch.

sorry, meant the small clone chorus, not the phaser.  Sometime when it gets put together I was going to try using a XR2206 frequency generator chip to get the sine wave, it as voltage controlled amplitude, might try a ramp thing like the Boss vibrato.  What I was thinking might be really nice (and unheard of with analog chorus/vibrato) is an LFO that automatically reduced the depth as you sped it up, so that the pitch change you hear stays the same as you change the speed, because with the bucket brigade type chorus/vibratos the pitch change is based on the slope of the rising and falling LFO.  I wonder if anyone has seen an opamp based LFO that does that already?

[Joe Kramer]

What I was thinking might be really nice (and unheard of with analog chorus/vibrato) is an LFO that automatically reduced the depth as you sped it up, so that the pitch change you hear stays the same as you change the speed, because with the bucket brigade type chorus/vibratos the pitch change is based on the slope of the rising and falling LFO.  I wonder if anyone has seen an opamp based LFO that does that already?

Cool idea.  The simplest way to do it would be with a dual pot, wired so that as the speed goes up on one section, the depth goes down on the other.  And, er, vice versa.