Univibe Phase 45 Help Please

[ncusack]

Hello Everyone,

I'm looking to build a phase 45 with the Univibe mod done to it with a Speed and Mix control. The closest thing I found out there in this kind of setup was this

http://www.youtube.com/watch?v=sGfGJiKX6HI

Would this kind of build just take the normal Phase 45 but change the caps for the Univibe settings and add in the Mix control from the JC Maillet Modded Phase 45 or would the depth knob in that video be like taking the 1M resistor off the trim to a 1M pot instead?

This would be my first build like this so any advise would go a long way.

Cheers,

Neill

[Mark Hammer]

You're close but, unless the maker of the video has misrepresented what they did, "depth" is something different.

There is a pair of 10k resistors near the output.  These provide an equal 50/50 blend/mix of dry and wet.  Maximum notch is achieved with a 50/50 blend, and less pronounced notching results from the dry signal side having a lower resistance than the wet side.  The "depth" control in the video you link to (which sounds much better than I expected, frankly) is likely subbing a pot of some value for these two resistors, with the wiper of the pot going to where they normally join and the two halves on each side of the wiper subbing for those 10k resistors.

Sweep width (i.e., LFO amplitude) is adjusted via the 3M9 resistor you note.  Dropping down to 3M gets you a wider sweep, and moving upwards to 4M+ gets you a narrower sweep, suitable for faster modulation.

"Offset" (where in the spectrum the notching/dipping is situated) is adjusted via the 1M resistor coming off the 250k trimpot.  Changing the value of that resistance moves the sweep a little higher, or a little lower, yielding different sorts of personalities.

[ncusack]

Thanks for the info Mark.

I threw together a quick board with the sections you mentioned with sockets so I can tweak things and I think i've found the sound im looking for. One issue I'm noticing is with a 500K speed pot is the variation in speed is clumped in the last 15% of the pots rotation. My build is set to use the univibe 10:1 ratio but I built it based on the stock phase 45 schematic. Looking at the JC Maillet univibe mods it shows a 4.1k resistor coming from the LFO to the speed pot and I used a 7.5k like the regular phase 45. Could the value difference here be causing the strange clumping of the control?

For reference the schematic im talking about can be found here http://www.lynx.bc.ca/~jc/phase45modded.gif

Note number 4 is the resistor im talking about.

[smallbearelec]

One issue I'm noticing is with a 500K speed pot is the variation in speed is clumped in the last 15% of the pots rotation.

Are you using a linear taper pot there? Probably you want reverse audio.

[ncusack]

Yes I am currently using a linear pot. Could i also use a smaller value linear pot with a resistor off one leg to narrow in on the speed sweep range?

[PRR]

Trem-Vibe speed controls, unless very narrow range, must be REVerse Audio taper to spread out the rates.

No, you can't fix this with a loading resistor.

(Alternative is a regular Audio and connect it backward so it turns backward: clockwise for slower.)