Looking for help with 'Vibe mod from Geofex site ( Dano Chicken Salad)

[danielzink]

Okay....

I've successfully rehoused a Danelectro Chicken Salad:

http://pws.cablespeed.com/~danielzink/salad.htm




Got rid of the switching board, fabbed up a bias supply etc. etc.

While browsing the Geofex site - I came upon this nugget.

A Single Pot Speed Control for LFO's - Univibe, Trem Face, and Others
Here's a trick to get rid of those pesky dual section, odd taper pots for speed controls and a way to get wider range out of your swept pedals that use the phase shift oscillator style sweep.

Where it really shines is in the univibe. The 'vibe uses a dual section, reverse log taper pot that's just a bit easier to find than a dinosaur's tooth. If we notice that the pot is really wired as two variable resistors, we can use an LED/dual LDR module like the VT5C3/2, which costs about $5 from Newark and other electronics distributors. To give us good control, we use a transistor to vary the LDR current. With a single 10K pot for speed, the transistor varies the current in the LED from nearly off to a voltage set by the V+ voltage minus the LED 1 voltage and the Vbe of the transistor. You take that voltage, divide by the max current you want in your LED, and insert that resistance into Re. The 'vibe circuit has resistors to limit the min and max resistance the circuit sees. I did this in my tube univibe, and it works great. You can mess with the taper of the single speed resistor (See The Secret Life of Pots) to adjust the effective taper of the speed control pot as you like it.

I emailed RG about it - he replied once - and I haven't heard from him for a couple weeks now. I'm sure he's busy and I don't want to be a pest so - I was hoping the collected minds here could help me sort it out.

The one reply I did get was:

On the dual gang pots - of the 6 tabs on the pots - only 4 are used - and 2
>of them are tied together. That makes for 3 connections - I've got that
>(per your schematic ie: "to speed control pads")
>
>I guess I'm kind of lost from there. I'm not sure where the 2 leads from the

>vt5c go to. Let's think a minute, and I believe you'll figure it out.

A dual pot with only four terminals used is the same as two variable resistors,
right? And with two of those tied together, you have, in effect, a single
center-tapped, variable resistor.

That is very much like the LDR in the Vactec module. What you want is to
find where in the circuit the two shorted-together pot terminals go, and connect
the center tap of the LDR to that place. Then connect the remaining
two terminals where the non-shorted-together pot terminals went.

Okay...I got that...

> As well as how to incorporate the transistor into the circuit.
That's the easy part. You only have to find two existing signals in the circuit -
+9V and ground, like the diagram shows. The two diodes, pot, transistor,
resistor, and LED terminals only share +9V and ground with the rest of the
circuit. So make up the pot circuit including diodes, transistor, resistor, and
probably the Vactec on a small bit of perfboard, then run wires from the
perfboard to +9V, ground, the actual physical single speed pot, and the
three resistor terminals from the output of the Vactec.

.....I think I broke something in my head....I'm still lost here....I have no ideas on values for the resistor, diode and transistor...

I can source the LDR module no problem here: http://optoelectronics.perkinelmer.c..._vtl5c2232.pdf

If it helps - here's the Chicken Salad schemo as well.....

[Mark Hammer]

Without wishing to put too much of a damper on your spirits, I'm not sure you really need to get into adapting the Uni-Vibe LFO for the Chicken Salad.

Here's why. The "magic" of any sweep-based optical modulation relies on the properties of both the photocell and the illumination source. If the illumination source is essentially instantaneous (which an LED is), then one does not have to adapt the LFO waveform to produce a desired illumination outcome that takes into account how quickly the light source gets brighter and dimmer. Part of what the Uni-Vibe LFO circuit does is adapt to the properties of an incandescent bulb that always takes longer to darken than to brighten up simply because of how heat dissipates from the filament.

The LDR/photocell itself doesn't particularly care if the illumination source is a bulb or an LED or a match for that matter. What it does have to do is provide the level of illumination needed in the region of the spectrum that the LDR is most (or at least reasonably) sensitive to. There is really no reason why you couldn't use the existing LFO, LED, and LDRs to achieve satisfactory modulation.

The one thing I would note is that Uni-Vibes are often best-sounding when the modulation amount is modest, so there might be a basis for reducing the or being able to more finely control the range of modulation.

[bob p]

If it helps - here's the Chicken Salad schemo as well.....

http://pws.cablespeed.com/~danielzink/csschematic.jpg

I tried that link, and the chicken salad schem is no longer on your site. Is the schematic still available? If so, I'd really like to see it.

I've been thinking about vibe projects lately, and one thing that I had been thinking about was tearing apart a chicken salad and tracing the circuit. If you've already done that, I'd rather not re-invent the wheel.

Has anybody got the chicken salad schematic?

[Regis]

I tried that link, and the chicken salad schem is no longer on your site. Is the schematic still available? If so, I'd really like to see it.

I've been thinking about vibe projects lately, and one thing that I had been thinking about was tearing apart a chicken salad and tracing the circuit. If you've already done that, I'd rather not re-invent the wheel.

Has anybody got the chicken salad schematic?

Bob, clear your PM box so I can send you a message.

[bob p]

done

[bob p]

Thanks to Dan and Regis for their prompt replies.

Just for reference, here's a schematic that is unsigned by its author. The basic circuit topology looks familiar.

[Groover]

Just for reference, here's a schematic that is unsigned by its author. The basic circuit topology looks familiar.

For those of us new to pedal-hacking, what circuit does this topology resemble?

[chris74]

Hi danielzinc

If possible please could you repost the pictures of your chicken salad re-house, i'm looking to do one my self and it would really help.

cheers

Chris