there are now tons of Univibe builders resources on the net ...
the main "official-DIY" collection, related to the work I've done,
is authored by
Brad Burt at
Classic Amplification ...
and goes by the name
"Forum Vibe" :
http://www.classicamplification.net/fv/files/fv_bld.htm
my old DIY page has some anecdotal material on the circuitry, and description of some of the mods that I've experimented with over the years
for example,
things like extending the frequency range of the oscillator, extending the effectiveness of the oscillator at slow speeds, ...
a Bias Offset control, which helps accommodate varying bulb specs (a mod from my early days)
>>> things that don't change the sound quality of the signal path, but may have a strong effect on effect performance
http://www.lynx.bc.ca/~jc/pedalsUnivibe.html
I've also looked at what happens when we use a high headroom preamp ... mu-stage with Presence and Volume controls
also, being able to switch between "stock" cap values, and Reslie Tone values
>>> things that change the sound quality of the signal path a little bit, but stays in line w original design
(vintage/modern)
I've also looked/analyzed/simulated variant LFO designs ... instead of using Darlington connected BJT's, I did some with jFET's and op-amps ... I've built some with all-jFET signa paths, instead of BJT's ... I have NOT done one with vacuum tubes, despite the many requests ... I might do one with all OTA's considering my recent 6G Brownface circuit discovery ... I'also used the LFO circuit in +/- 9 volt supply situations, with zero-adjust to accomodate DC coupling // thus avoiding the losses incurred by signal caps typically included around the DEPTH control ... I've also done Vibes using threshold/ratio adjustable voltage-to-resistance converters to produce ulra wide-range Phasing, where cells go between 10Meg ohms and 100 ohms under controlled situations ... in a stock vibe they typically go about 1Meg to 1k using wide-range cells and properly darkened environment, correct bias/gain on bulb driver, etc ...
you can either build yourself a faithful replica of the original Vibes, or play with a bit of variety
I like both ... in my collection I still have a few of my very first builds, and are just as inspiring to play
maybe, even more ...
---
as far as functionality goes
the pedal can be used as originally meant, ie., not direct-bypass and only with an oscillator kill switch ...
leaving the gtr signal going thru the whole circuit still
or have direct bypass, bypassing the preamp and everything
obvious to us who know, Jimi's tone was affected by the presence of the Vibe's signal path when he used one ...
so, obviously, if you're trying to copy his tone to the very last drop // yeah, go that route
these are all options to consider here ...
---
format wise,
Classic Amplification has a retro-fit board (the "Vibe Baby") that fits in a Cry Baby pedal
https://www.youtube.com/watch?v=6p5AP1xKnBk
sounding pretty good !
---
of course, the circuit is a little tricky to make happen
so, if you're going to build your own, you should know the following:
first, the quality of effect here obviously depends on choosing photocells carefully,
and the right bulb ...
the importance of the later (slow/fast bulb cool-down) may be a big deal for some, not so much to others ...
that's a personal choice
but more so even, adjusting the drive on the bulb,
and also making sure that the cells are in a light-tight environment
that part is crucial and easily overlooked ... even light creeping from the in/out jacks could affect things
that's why a light shield is used
you may also want to tape up the bottom of the PCB as well (!!)
that's often the main mistake when a vibe sounds lame, even with good cells ...
and the reason for the bias offset adjust mod
a key condition is providing proper darkness to the cells ...
since much of the action happens when the cells are in the high resistance range
so, if the bulb is biased too hot and never comes close to turning dark, you will have little effect depth
light shielding is especially important to remember in Wah-Pedal builds, as stage lights can bounce inside from the treadle opening in the pedal and go thru the underside of the PCB, depending on its material composition of course ... effectively neutralizing the cells ... just make sure to give that side of the equation its due consideration and you'll be in good shape
... of course, we also want to make sure all your cells exhibit appropriate cell-resistance range
which is dead easy to verify using a common desk lamp and ohm meter (any plain DMM will do)
grab your meter and some alligator clip wires and see what your cells measure about a 18 inches away from a 40w/60w bulb
aimed "straight-on" into the face of the cells
they should be under 1k ohms preferably, or close to that value ...
bring the cells under the desk and cup your hands around them to block out light
if you can, avoid touching the leads to the cells
you should be able to see at least 500k of resistance,
even (preferably) going off-scale when the DMM is set to 2M range
set aside four cells that exhibit similar response to this 2-state (crude) light test
do not include cells that seem to take too long to stabilize in the above test ...
cells don't have to be perfectly matched ...
but, similar to jFET's used in other Phasors, you want all cells to have similar resistive "dependence" to light
it's not so much the exact/rough "end" values, as they usually don't exist, but more the range response to light
the simple test describe here above is sufficient for this purpose
as it verifies that resistance goes very high at low light, and very low at on-light ...
otherwise the cells is considered "stuck" and useless for this task
in other words, you want wide-range cells ...
those that go below 1k (light) and well above 500k (dark)
---
which cells to buy ? ...
not sure, I have a stash of old cells that I bought years ago in a surplus shop
Steve at smallbear used to have "boutique" grade cells but I can't find that label now ...
you'd have to contact him and see which one the "vibe" guys seem to prefer
or, contact Brad Burt at Classic Amplification ...
he works on lots of original Vibes and I consider him to be the expert now, if anybody
needless to say, patience is paramount here ... the bulb bias alone is a real balancing act
and can take a few days of going back and forth before nailing the response
I hope this info helps // good luck on your build ..!!
~jcm