Custom Vibrato effect - Analog or digital?

[Duke S.]

Hey guys! I've been lurking r/diypedals and diystompboxes a bit and am trying to get back into a hobby I first got into while going for my CE degree ~7 years ago. I built a fuzz and tremolo back then, and am trying to come up with a vibrato effect now.

I'd say this effect is significantly more difficult than I remember the other 2 being - I get the gist of it: Generate an lfo, and have that modulate the frequency of the guitar signal. I've got a triangle wave generator that's driving a jfet to a vibrato circuit I found online but when I breadboarded it, it ended up sounding like a tremolo. I copied the top right portion of the circuit and tried my own LFO for the bottom left portion (My LFO is a triangle between .6 and 6 volts - maybe that's too much amplitude? I never really worked with jfets) 

The part I'm really struggling with is changing the frequency. Like, how would you actually take the signal and bend its frequency back and forth. I've heard a lot about phase shifting being a way to do that, but I can't wrap my head around how that works at the moment 


Mainly just looking for pointers or someone to tell me to give up and try a microcontroller (any good recommendations?)

Here's what I'm working with so far https://drive.google.com/file/d/1dU6XIzR1iwxqOfrGgDg9iMUguORtzh8V/view?usp=drive_link

[merlinb]

Vibrato is a pretty advanced topic in discrete analog design, it doesn't really lend itself to 'simple' circuits. Try reading the vibrato section of stompboxology:
https://www.dropbox.com/scl/fi/8xzg7qsgwqa5cp35lzhsw/Vibrato_Stompboxology.pdf?rlkey=z4ar0or8t2zbbtotqo1yns4wv&st=c3gnbwrh&dl=0

I would recommend building a phase 90. It's well documented, and it works by generating vibrato and then mixing it with the original dry signal. If you switch off the 'dry' path then you just get the vibrato, so you can have two effects in one.

[antonis]

Hi & Welcome..

+1 to what Merlin said..

https://sound-au.com/project49.htm

P.S.1
About LFO: It should create sinewave output (with the lowest possible THD), especially when driving a transistor..
(there are plenty of RC phase shifters/Twin-T/Wien oscillators good LFOs, with either BJTs or op-amps..)
P.S.2
T3 and relevant circuitry above needs ideal world conditions to work as phase splitter and then shifter..
(e.g. intrinsic Emitter resistor is added on R8 while Collector output resistance is set in parallel with R7.. Collector /Emitter currents inequality is an additional "burden"..)

[Mark Hammer]

Vibrato can often sound "best" when modulated by a sinusoidal waveform.  Indeed, I think the best and most laudable thing about the much-venerated Boss CE-1 is that it not only provides chorus and vibrato in one pedal, but that it employs a different LFO waveform for the two effects; "rounding off" the triangle used for chorus to something more sinusoidal for vibrato.

I built a few Magnavibe clones for myself.  These are fairly similar to the schematic posted by the OP, except for their use of an LED/LDR pair.  It provides a nice gentle wobble that one doesn't quickly grow tired of.  I also built a stereo unit, that split the input into two independent copies of the same circuit, fed to two amps.  Using two unsynced LFOs with a master rate and intensity control (dual-ganged pots) yielded an absolutely delicious and immersive stereo effect. 

The unsynchronized LFOs are critical to the effect.  The original Magnatone amplifiers, that the Magnavibe is an adaptation of, did have a "stereo" implementation of their vibrato effect.  Although the unit employed two independent power amplifiers and speakers, the modulation of the vibrato effect came from countersweeping via a common LFO that made one side go a little sharp as it made the other side go a little flat, making the wobble go back and forth; a bit like an auto-pan, except for pitch.  I find that unsynced LFOs do a much better job of yielding a richer effect in stereo, because the movement is not predictable.

[Duke S.]

Thank you guys for the helpful replies, I'll check out these links tonight after work.

Side note: Do I have to do these verification captchas and answers every time I post or reply here? 

[bluebunny]

Take a look at the Tri-Vibe at runoffgroove.


___
(The captchas stop after a few posts.  It's to discourage spam and bots.)

[ElectricDruid]

It's not been made explicit, but there have been two approaches offered here.

1) Phase shifting
If you build some phase-shift stages and then wobble them about with an LFO, you get a vibrato. This happens because frequency is rate-of-change-of-phase, so if you muck with the rate-of-change-of-phase, you muck with the frequency.
The design you started with is a simple-as-possible phase shift stage.

2) BBD based
Mark mentioned the CE-1. If you sample the signal into a BBD using a clock and then vary that clock using an LFO, you get a variation in the frequency of the signal going through the delay line. That happens because some of the samples are read out faster than they went in (so the pitch gets shifted up) and some get read out slower than they went in (so the pitch gets shifted down).

Both of these are valid ways to go, and both approaches can be done digitally too. There are examples of all the variations.

HTH

[bluebunny]

Well said, Tom.  Clear explanations too. 

The Tri-Vibe is an example of the former.  I'm barely qualified to tie my own shoelaces, so I leave it to the ROG boys to explain everything on their project page.  BTW, it sounds cool too.

[Mark Hammer]

The Tri-Vibe is a nice circuit that provides a decent, if subtler, Vibe sound, along with vibrato.  I packed one into an enclosure, along with an overdrive (Vibe before drive) that gives me a Robin Trower-like sound.

[Duke S.]

I went ahead and breadboarded that tri-vibe circuit, exactly what I was looking for - thanks everyone!

[Mark Hammer]

Congrats!