Juicin' up my Neovibe Build

[Astronaurt]

Hey y'all, So after many moons have passed with my pedal workshop in storage, I just broke it all out last week and FINALLY finished building my Neovibe. I'm pretty jazzed about it because I've always wanted a Univibe style effect to play around with, and pretty impressed that it worked right from the first time I plug it in!

I used the PCB from General Guitar Gadgets: https://www.generalguitargadgets.com/projects/20-modulationecho/121-neovibe
and R.G.'s schematic here: http://www.geofex.com/FX_images/vibeschm.pdf
Ended up fitting it very nicely into a Rocker Pedal from Small Bear, and used the Single Wah Pot/ Optocoupler idea from the UVICS design for Speed Control

There's a couple things that I'll get around to tweaking tomorrow for sure...

The only big oddity is that when I turn the Depth Pot all the way up, the Lamp stops responding- I'll turn it back down 1/10 of a turn and the Lamp lights up again. Not the end of the world, but somewhat annoying. I'm wondering if this has happened to anyone else? The Lamp I have is a RadioShack 12v/60ma.

More a nuisance, I feel like the Speed Control doesn't get as fast as I have heard Univibes get. The LDRs I've used in the Speed Control Optocoupler have a pretty wide range between 100Ω to 5MΩ, So I was thinking perhaps putting a parallel resistance (=220K, 470K, or 1M, which I have lying around) with the LDR's could make the circuit see a more usable Speed Range? Otherwise I know that reducing the 4.7K, R42 and R43, resistors should give a faster speed limit?

Other than that, I'm interested to hear what people think of some mods to the stock Neovibe Circuit? Any that really made the difference you were looking for, or that didn't have a noticeable result? Let me know what you think! Thanks y'all, I'll post some pics when I get back home tomorrow.

[midwayfair]

Reduce the two 4.7K to increase the speed. You can't go much lower.

Your next best bet if you just want to shift the total speed upwards is to replace the three 2.2uF caps in the oscillator with a smaller value, like 1.5uF or 1uF. This will speed things up a lot.

Does your depth issue occur (1) at all speed settings and (2) at all gain trimpot settings?

[R.G.]

The only big oddity is that when I turn the Depth Pot all the way up, the Lamp stops responding- I'll turn it back down 1/10 of a turn and the Lamp lights up again. Not the end of the world, but somewhat annoying. I'm wondering if this has happened to anyone else? The Lamp I have is a RadioShack 12v/60ma.

It's not a lamp problem, it's an LFO problem. The LFO in the univibe is a special case version of a phase shift oscillator. When it goes too fast or too slow, it runs out of either impedance to create gain or phase shift to make it oscillate. When that happens, it stops oscillating until the conditions become right again. It can be made faster or slower, but not much wider range in speed without some serious rethinking of how it works.

You can so somewhat better by changing Q11 for a higher-input-impedance device. A JFET or Darlington works well. I'd have to do some looking at the datasheet, but this may be one place that a J201 is really good. An MPSA13 or 14 ought to improve things a bit as well. But really serious increases in range require a redesign, not tinkering.

More a nuisance, I feel like the Speed Control doesn't get as fast as I have heard Univibes get. The LDRs I've used in the Speed Control Optocoupler have a pretty wide range between 100Ω to 5MΩ, So I was thinking perhaps putting a parallel resistance (=220K, 470K, or 1M, which I have lying around) with the LDR's could make the circuit see a more usable Speed Range? Otherwise I know that reducing the 4.7K, R42 and R43, resistors should give a faster speed limit?

See above, plus now the bulb gets into it. An incandescent bulb has a built-in speed limit. It only heats up and cools down so fast. If the LFO tries to go faster than the bulb can heat and cool, the bulb just kind of smears the brightness variation. Smaller current bulbs and physically smaller bulbs will be faster. LEDs are near-instantaneous, but purists like some of the original smearing and sneer at LEDs.

The dual LDR is indeed much wider range than the stock resistors let it be. But that may not help.

You can shift the range up and down by changing the value of those three stacked 1uF caps. Smaller is faster, bigger is slower.

Other than that, I'm interested to hear what people think of some mods to the stock Neovibe Circuit? Any that really made the difference you were looking for, or that didn't have a noticeable result? Let me know what you think! Thanks y'all, I'll post some pics when I get back home tomorrow.

The world is filling up with people who have tinkered with the univibe. It was one of the first DIY effect on the internet (I know - I put the layout on usenet), and pre-dates the introduction of web surfing. So you'll likely get lots of opinions. They're out there. And opinions are like - er, noses  - everyone has one, and they all cause about the same amount of trouble.

[Astronaurt]

Update:

Thanks for the input guys!

I've been dicking around with everything and getting good results. As it turns out, first thing I found was a loose connection on one of the Optocouplers' LDR's that I socketed in (Durr) so I snapped that firmly into place and all of a sudden my dragging speed control got super fast! In addition, my depth pot now continues working all the way to 100% (I figure now that both the LDR's are actually connected there's enough phase shift getting back to keep it breathing), albeit in the last 1/10th of a turn the depth pot actually decreases apparent Amplitude while increasing the apparent Frequency? Again: weird; but the whole effect is weird but now I'm fine with where it's at.

Now I have an opposite problem from before though: Instead of not getting enough speed, I now don't have much middle range at all between Slow and Fast speed. I'm chalking it up to the LDR's being VERY Light dependent- and there's not much space of a turn on the Wah-pot between LED 'Fully Off' and 'Fully On.' I changed the Rocker pot I'm using to control the Optocouplers from a Linear to Audio taper and though it made a noticeable difference, it was not as much as I'm looking for. With the speed control up past about 1/2 of it's rotation it's already at full high speed.

I've already got a 1K Trim between the LED Drivers emitter and the 2 LED's, so I'm thinking if further reducing current by increasing that resistance would force the LEDs to go hungry and light up a little slower and smoother across the sweep? Or would it make more sense to deal with this issue on the Transistor and Rocker pot side of the circuit? My end goal right here is just to get the Speed Control to be working smoothly over its full range. Just to throw it out there, my Optocouplers are somewhat Jerry-rigged: no-name LDRs stuck to no-name LEDs with Heat-shrink tubing, so I'm going to try swapping this pair out for another combination and see if that cleans it up too, I know those things never have tight tolerances.

Alternatively, R.G., I was looking at your "Single Pot Speed Control" article:
http://www.geofex.com/circuits/ldrlfo.htm

and saw the circuit there is slightly different from the one that I used for speed control, outlined in the U.V.I.C.S. project file, Page 6:
http://www.geofex.com/FX_images/UVICS-3%20Project%20File-3.pdf

Does the addition of Diodes on the pot and placing the LED on the V+ side of the Transistor give a better range of LED control, or is it functionally equivalent?