Univibe lacking

[Nostalgia]

Hi there, I got this new Univibe clone. It sounds ok but that " heart bit" pulse pattern is very faint. Can I improve it by simply changing the photocells or lamp?

I would also love it to add a little more Phasing effect. What can I do to improve these things?

PS: Where is the best source online to buy some quality Photocells and bulb?

Thanks in advance!

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[Mark Hammer]

As I discovered when repairing someone's shutter-based Morley pedal, when a circuit uses a lamp of some sort and separate photocells, both the brightness of the light source and position of the photocells can make a difference.  bend them back a few degrees, and you can lose a lot of oomph.

Note as well that the Uni-vibe circuit does not produce pronounced and focussed notches and peaks like a phaser does, but yields broad and shallow "dips", with no peaks (vibes do not come with a feedback control...ever).  As a result, a big part of what yields the "heart beat" you speak of is where in the spectrum such dips are situated.

The tuning of where the dips are is a function of 3 things:

• the values of the caps
• the illumination of the light source
• the responsiveness of the photocells to the light source

Realistically, that's only two things, being the C x R (photocell) value as determinant of where the phase-shift is maximized, but the photocell resistance depends on the properties of the photocell, whether it is positioned to "catch" the light available from the source, and what's shining on it.  If a photocell is bent back a bit, and the light source is very bright, or generally very dim, then there may not be much useful fluctuation in the photocell resistance as the light source varies, with the result being that you don't get to hear as pronounced an effect.

So, bottom line, you may not have to change anything, beyond making sure the photocells are all seated optimally, and the brightness of the light source yields decent fluctuation in illumination and corresponding photocell resistance.

[midwayfair]

As I discovered when repairing someone's shutter-based Morley pedal, when a circuit uses a lamp of some sort and separate photocells, both the brightness of the light source and position of the photocells can make a difference.  bend them back a few degrees, and you can lose a lot of oomph.

It's the amount of difference between the lowest and highest resistance of the photocells that matters for this. You want the photocells to swing very low but you also need them to swing to extremely high resistances, well over a couple megaohms ideally.

This involves multiple things.

First, the photocells have to be far enough away from the light source that the lamp's "cooling off" period won't keep them full lit, but close enough that they're driven to their lowest point when the lamp's all the way on.

Second, your photocells need to be capable of huge swings. Smallbear actually sells photocells they had specially made for this and they'll usually work right out of the gate shoved up against the lamp because their dark resistance is absurd.

Third, your lamp needs to be dialed in. The Madbean version at least uses multiple trimmers to set the lamp. You're looking for the biggest swing you can get with the lamp's brightness.

Oh, and obviously, don't test any settings with the back off. The circuitboard has to be in complete darkness to work properly.