Vintage SHINEI UNIVIBE – restoration and enhancement

A couple of years ago I thought I’d spend my life savings on a 60’s SHINEI Univibe phasor. I managed to track one down on eBay and immediately fell for it!

The unit was dead right out of the box and I immediately applied for a refund. Though, except for a few obvious “mods” and some replaced electrolytic caps, everything crucial seemed original. Boxing it up after taking a quick look inside brought it life – with intermittent behaviour …

Someone had tacked on a DC relay circuit, using one of the input jacks for switching the relay on/off.

… and some kind of booster/preamp add-on, possibly an LPB-1 type of affair, had been rigged in one corner (?)

otherwise, everything else – cells and all – seemed original and in ok shape …

First, to find out why the unit was operating intermittently I had a look at the underside of the board – whereby I found a couple of obvious culprits …

the circuit began to work reliably and I then made the decision to cancel my refund request with eBay …

COMMITTED

After removing the booster circuit and the relay circuit, I rewired a proper ground wire and installed the two stock 22k resistors leading to the input jacks, restoring their original correct function in the process.

A dual 100k log pot had been wired backwards into the foot-pedal connector – I left it as is for now …

Turns out, regardless of the bias control setting on the bulb driver circuit the phasing response I got was somewhat wimpy.

By observing the operation of the bulb I could see where the two main parameters were set:

the AC gain was too low, and the DC offset was set too high by the two fixed biasing resistors – not an un-common thing with this design (!)

BULB DRIVER MODS

After replacing the two biasing resistors by an equivalent trimpot (google “Univibe Bias Offset Mod”) and then also playing a trick on the stage to produce whopping amounts of light while at the same time as setting the “edge of darkness” in the light response – a balance that is crucial in getting deeper Vibe’ing – the unit suddenly came alive!

here’s a brief glimpse of the pre-mod/post-mod driver settings in action :

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