neo vibe univibe clone

[tom]

I'm building the neovibe from the pdf instructions i got from general guitar gadgets/geo. i have a question about r 35 and r36 , they are supose to be 100k resistors. the instruction recomend hooking up a 200k pot and tuning to best sound then measuring the wipers and put in the closest 1% resistor. how do i hook up the pot, is it necessay?

I'm sure i have more questions later

Tom

[petemoore]

r 35 and r36 , they are supose to be 100k resistors. the instruction recomend hooking up a 200k pot and tuning to best sound then measuring the wipers and put in the closest 1% resistor. how do i hook up the pot, is it necessay
 My guess is that they are a divider, two 100k's in series, the middle connected to something and the ends of the seriesed pair connecting to V- and V+?
 At any rate using a pot as a voltage divider is as easy as tieing two resistors together [at one end each] so you have three leads.
 Lay the two resistors in seriesed pair...the ends would be replace by the outside lugs of the pot, where the two connect you'd connect the wiper.
 Linear pot will do more of a 50/50 split to 60 /40..audio taper...that's all typed out at GEO 'secret life of pots'.
 You can get the resistance [100k pot: you get 200k Resistance  but not 200k variable], up by using the pot with outside resistors on it down with insdie resistors.
 Tapering aside, within limits you can adjust size and taper of pots to your needs with fixed R's/
 Try a 500k in cardboard, so you can turn it ez, DMM R value readings attached, and connect both ends of a 470k [try different values] to the outside lugs of the pot...two 200k's from each outside lug to wiper...
 See what kind of tapers one size pot is capable of...and post the results so I can check it out!!!
 Getting some V/R on there sure would be easier than socketting and or otherwise twiddling with resistor values. Then pull two [one outside] leads from the pot connection [careful not to touch..so the pot stays set where you had it] and measure the R  values with the DMM and replace with fixed resistors.

[Alex C]

Here's what R.G. says in the pdf file about the Neovibe:

"There is a very little-known secret to getting good, deep phasing out of phasers in general and the ‘vibe in particular.  The depth of phasing depends on getting a good mix at the output. Resistors R35 and R36 mix the dry and phase-delayed signal together. The stock values may not be the right one for a good mix. If you want the best performance
out of your Neovibe, leave these two resistors out and use a 200K pot to adjust the mix for deepest phasing. Then measure the resistance on each side of the wiper and put the nearest 1% resistor values in for R35 and 36."

To do this, you will wire the middle lug of the pot to Pad N (or the "chorus" side of the chorus/vibrato switch) and the outer lugs to the pads where R35 and R36 would go.  Then you measure the lugs and sub in the appropriate resistor to its respective lug.  I think that's it.

Alex

[R.G.]

Thank you Alex - yes, that's it.

Tom - using a pot for that bit of fine tuning is not strictly necessary. Chances are you can get along just fine popping in 1% metal films or even 5% carbon film resistors and be happy. Sometimes this does not result in a great phaser sound (even on real, honest-to-God Univibes) so I wrote the tuning down for people to tweak their own units in for great sound.

Do NOT ground the AC power input jack to the (presumably) metal box if you use the suggested AC power supply. This shorts out the internal power rectifier and lets white smoke pour out of the jack-holes. Not to mention frustrating the heck out of you.

[SteveB]

I have 2 100k's in mine. For the sake of experimentation, would the value of each still have to add up to 200k? Hypothetically, say a 120k on one side, & a 80k on the other?

Thanks,
Steve

[Tychobrahe1979]

I tried the fine tuning with a pot and I could not hear any difference from my 5% 100k's that were in there.