Adjusting UniVibe Maximum Speed

[Big Monk]

R.G.'s "Technology of the UniVibe" article states the 4.7k/220k/100kC speed control network dictates the min/max speed characteristics of the pedal.

http://www.geofex.com/article_folders/univibe/univtech.htm

Would one raise or lower the 4.7k to increase maximum speed?

Would one raise or lower the 220k in parallel with the speed control to lower minimum speed?

[bean]

Lower both 4k7 resistors. Socketing is a good idea. You can often lower them to around 2k2. I think in the MojoVibe they are 1k8. But, do keep the same value for both. You'll know if you've gone too far b/c the LFO will either lock up or will be too fast to hear the depth pulse.

[bean]

Whoops, I forgot to mention in the MojoVibe the Speed control is handled differently than a traditional UniVibe (it uses a vactrol) so that may be why the max speed can be tweaked so high.

[Big Monk]

Whoops, I forgot to mention in the MojoVibe the Speed control is handled differently than a traditional UniVibe (it uses a vactrol) so that may be why the max speed can be tweaked so high.

I'm in a bit of a pickle because I have a PedalPCB Electrovibe I just finished and Speed 2 has a much lower maximum speed than Speed 1. I think tolerances may have messed me up. I'm going to grab a gang of dual gang 100kC pots and match a set and replace both.

Your info, however will be useful for increasing the maximum speed once I get them equal in Speed.

[bean]

Whoops, I forgot to mention in the MojoVibe the Speed control is handled differently than a traditional UniVibe (it uses a vactrol) so that may be why the max speed can be tweaked so high.

I'm in a bit of a pickle because I have a PedalPCB Electrovibe I just finished and Speed 2 has a much lower maximum speed than Speed 1. I think tolerances may have messed me up. I'm going to grab a gang of dual gang 100kC pots and match a set and replace both.

Your info, however will be useful for increasing the maximum speed once I get them equal in Speed.

I don't think you need to do that. If I understand correctly, the speed switch just toggles between two dual gang 100kC pots? In that case, just always use Speed 2 for your low speed and Speed 1 for your high speed. Then you don't have to replace anything.

Without seeing a schematic I can't speak intelligently about it, but it seems easier to just put two resistors in parallel with each gang on one dual pot to create slow and high speeds. That way your max high speed will always be the same, and the two speed settings would only differ in their slowest speed. But, I might be missing something.

[Big Monk]

Whoops, I forgot to mention in the MojoVibe the Speed control is handled differently than a traditional UniVibe (it uses a vactrol) so that may be why the max speed can be tweaked so high.

I'm in a bit of a pickle because I have a PedalPCB Electrovibe I just finished and Speed 2 has a much lower maximum speed than Speed 1. I think tolerances may have messed me up. I'm going to grab a gang of dual gang 100kC pots and match a set and replace both.

Your info, however will be useful for increasing the maximum speed once I get them equal in Speed.

I don't think you need to do that. If I understand correctly, the speed switch just toggles between two dual gang 100kC pots? In that case, just always use Speed 2 for your low speed and Speed 1 for your high speed. Then you don't have to replace anything.

Without seeing a schematic I can't speak intelligently about it, but it seems easier to just put two resistors in parallel with each gang on one dual pot to create slow and high speeds. That way your max high speed will always be the same, and the two speed settings would only differ in their slowest speed. But, I might be missing something.

My issue is that I want to rule out a bad pot. If it were a negligible difference or even a small one, I'd live with it like you suggested and just devote the slower of the two as my slow speed.

The problem is that Speed 2, at its maximum is about 40% slower than Speed 1. That leads me to believe it's a big variance between the actual pot values due to tolerance, or an issue with my build in particular.

[bean]

The problem is that Speed 2, at its maximum is about 40% slower than Speed 1. That leads me to believe it's a big variance between the actual pot values due to tolerance, or an issue with my build in particular.

So, for a stock Univibe the max speed is achieved when the dual ganged pot is turned up all the way. That means there is zero resistance across the pot. IOW, both gangs of the dual pot are shorted and only the two 4k7 resistors are present and those determine the max speed of the LFO. In that case a difference in tolerance between two dual gang pots should not matter because that difference would only be apparent in their respective slowest speeds.

But, again, without a schematic I cannot say why the two fast speeds are different. If there are two different sets of "stopper" resistors for each speed pot that might explain it.

[Big Monk]

The problem is that Speed 2, at its maximum is about 40% slower than Speed 1. That leads me to believe it's a big variance between the actual pot values due to tolerance, or an issue with my build in particular.

So, for a stock Univibe the max speed is achieved when the dual ganged pot is turned up all the way. That means there is zero resistance across the pot. IOW, both gangs of the dual pot are shorted and only the two 4k7 resistors are present and those determine the max speed of the LFO. In that case a difference in tolerance between two dual gang pots should not matter because that difference would only be apparent in their respective slowest speeds.

But, again, without a schematic I cannot say why the two fast speeds are different. If there are two different sets of "stopper" resistors for each speed pot that might explain it.

Maybe this will help:

https://www.pedalpcb.com/docs/ElectroVibe-Schematic.pdf

I'd appreciate any help. I'm a savvy troubleshooter with the right direction.

EDIT: Per your description, it sounds like at maximum, I have some stray resistance on Speed 2.

[PRR]

For faster/higher, it is often best to leave the resistors alone (they are picked for DC and loading) and change the capacitors (1/[R*C]).

[Rob Strand]

I'm in a bit of a pickle because I have a PedalPCB Electrovibe I just finished and Speed 2 has a much lower maximum speed than Speed 1. I think tolerances may have messed me up. I'm going to grab a gang of dual gang 100kC pots and match a set and replace both.

If you have a DPST switch shorting one of the pots then one would be much slower than the other.

If you have a DPDT with the poles between the pots then it selects between the two pots  and both pots will have more or less equal range.  Basically shorting out one pot or the other.

EDIT: Per your description, it sounds like at maximum, I have some stray resistance on Speed 2.

To me it seems like you have the wrong switching.

[Big Monk]

I'm in a bit of a pickle because I have a PedalPCB Electrovibe I just finished and Speed 2 has a much lower maximum speed than Speed 1. I think tolerances may have messed me up. I'm going to grab a gang of dual gang 100kC pots and match a set and replace both.

If you have a DPST switch shorting one of the pots then one would be much slower than the other.

If you have a DPDT with the poles between the pots then it selects between the two pots  and both pots will have more or less equal range.  Basically shorting out one pot or the other.

EDIT: Per your description, it sounds like at maximum, I have some stray resistance on Speed 2.

To me it seems like you have the wrong switching.

The pedal uses a 3PDT as a speed switch with the extra poles used to switch a bi-color LED.

[Big Monk]

I found the issue!

The dual ganged pots were sitting to high when I installed them and the lamp was hitting the inside of the lid.

When I re-seated them, it appears I lifted the pad on the wiper of the top gang of Speed 2. It lost its jumper to Pin 1.

Soldered in a manual jumper and Viola! Equal speeds. Now I just want to play with getting more speed out of each.

[Big Monk]

For faster/higher, it is often best to leave the resistors alone (they are picked for DC and loading) and change the capacitors (1/[R*C]).

I've been out of the EE curriculum for for 7 or so years now but my brain says smaller time constant means faster speed means make the capacitors bigger? Do you change all three caps?

[duck_arse]

faster speed means smaller capacitors, shorter charge/discharge cycle times.

[Big Monk]

Thank you for all the great replies. So much useful info.

[Kevin Mitchell]

I think I had used .68uF electros for one of my clones. Definitely gave the range I was hoping for and plan to do the same to every Vibe clone moving forward.

[Big Monk]

I think I had used .68uF electros for one of my clones. Definitely gave the range I was hoping for and plan to do the same to every Vibe clone moving forward.

A few things...

Firstly, I sorted out the differing speed issue. When I was trying to seal the dual ganged PCB pots closer to the board, I lifted the wiper trace on Speed 2. Since there was no longer continuity with the jumper trace to lug 1, I was not getting maximum speed. I added a manual jumper and Viola!

I ended up changing the 4.7k resistors to 2.7k and there was a nice bump in maximum speed. Nothing crazy, and I had no issues with the lamp, but enough to satisfy me.

I also own an EHX Good Vibes, which has a ton more speed available. I'll be comparing the 2 in the next few weeks and deciding which stays. The Good Vibes seems to have more "oomph" than the Electrovibe. To me it sounds like it has more mids/lower mids and bottom.

I originally wanted to build the Electrovibe because of the foot switchable speed controls, as my Good Vibes controls speed through and expression pedal output and it takes up board space. What I'm learning is that the Good Vobes, contrary to many of the reports and reviews I read online, is a wonderful Univibe pedal at a great price, even factoring in the cost of the Expression pedal. 

[Rob Strand]

I also own an EHX Good Vibes, which has a ton more speed available. I'll be comparing the 2 in the next few weeks and deciding which stays. The Good Vibes seems to have more "oomph" than the Electrovibe. To me it sounds like it has more mids/lower mids and bottom.

I don't know what the EHX Good Vibes does but you can play around with the cap on the all-pass filters.   The Univibe has it's own sound.   You could easily make all the all-pass cap the same and push into MXR phase 90 territory.     The point I wanted to make is there's plenty of room for experimentation in between those two extremes.   All it takes is a switch and a few caps to play.

[Rob Strand]

I don't know what the EHX Good Vibes does

Looks quite different to a Univibe to me!  Perhaps delay based not all-pass.

[Big Monk]

I don't know what the EHX Good Vibes does

Looks quite different to a Univibe to me!  Perhaps delay based not all-pass.

Agreed. There are rumors it might be getting traced at PedalPCB and I would welcome that. I'd love to see what makes it tick.

If biased right the classic UniVibe sound is there.