This Week on the Breadboard: ROG Tri-Vibe

[Chuck D. Bones]

Yes, that could work, but I don't know how well. The LDR resistance range and rate of change are highly variable. You need to select just the right LDR for the job. Seems a bit kludgy to me.

The STOMPLFO eliminates all of the unknowns, and by replacing the LFO circuit with a single chip, uses fewer parts.

 

[Diynot]

Shit, already built a harbinger 2, but a tri-vibe in a wah shell would be amazing and apparently there is one manufacturer out there that makes a 500k ICAR pot (Joe Gagan). Is there a way to get the same speed spread with a 200k, or at least adjust to shift the speed to a higher or lower speed range? Is it as simple as putting these caps on a switch (from the Aion schem):

Or would you put R27/R28 on a switch instead with values increased to accommodate use of a 200k pot?

 

[Chuck D. Bones]

This points out another advantage of the STOMPLFO: the RATE pot can be any value and the range remains the same.

Increasing C9 & C10 is one way to accommodate a smaller RATE pot value. You'd better use tantalum because aluminum caps are leaky and might cause the LFO to stall.

There is another way to connect the RATE pot, which accommodates different pot values without fiddling C9/C10.
Remove R27.
Connect pin 3 of the RATE pot to IC3-7.
Leave RATE pin 2 connected to R28.
Connect RATE pin 1 to one end of a resistor and the other end of that resistor to Vb.
Select the values of the new resistor and R28 based on the RATE pot value and the desired speed range.
Another advantage of this connection is by carefully selecting R28, we can obtain a broad range of effective tapers.
(See the EQD Space Spiral's LFO for an example of this connection)

I have a question for you: would you actually use the full-range of the Tri-Vibe's speed?

 

[Diynot]

Awesome! Thanks for the info. I will check out the dark rift schem. As far as using the entire speed range? Maybe. I definitely liked almost the entire range of speeds on my tri-vibe build. That and since there are 3 modes I feel like they each sounded best at slightly different speed ranges.

 

[Chuck D. Bones]

I mention the speed range because it's much easier to select a speed with a knob compared to a treadle. The larger the range, the harder it is to hit a specific speed. The UniVibe did not have a huge speed range.

 

[Diynot]

Gotcha. The draw for me wouldn’t be for hitting a specific speed, but doing the Leslie speaker tones/ramping like @cooder mentioned.

 

[cooder]

Here's my functionality wishlist:
two footswitches, bypass (obviously) and ramp up/down
four pots: depth/ speed (low) / speed (high) / ramp speed
toggle switch for the three modes

Which sounds pretty much like what @Diynot said.

 

[Chuck D. Bones]

That's what I had in mind also. Once Steve's New Years Design Contest is over, I'll get on it.

 

[Diynot]

Happy birthday Mr Wizard! Once the raging CDB bday extravaganza is over, will there be some movement towards developing this sweet sweet circuit? Purty please!