Univibe Build

[Spencerleehorton]

Hi Guys,

Just built a Univibe (an old pcb i had lying around form years ago and thought i'd get it working again)
Seems to power up ok, bulb is working, no smoke!!! plugged it in to see if i get signal and phasing but i get signal through it, volume works but no phasing sound at all?
The photocells in there are from 20 years ago, is it possible they have gone?
Im not that familiar with how to check if photocells work or not, i can see voltage on them so im assuming they work and there is something wrong somewhere else in the circuit?
If anyone could point me in the right direction please?

regards

Spence.

 

[PRR]

Power off. Put ohm meter across LDR. Wave hand between room light and LDR. Does the meter change?

 

[Spencerleehorton]

Yeah,

photocells were fucked!!, works like a charm now!! happy days!!

onto the MXR Flanger now and finish the phase 90!!!!

 

[Spencerleehorton]

have got a madbeans Harbinger one pcb and im going to compare this to the original.
Im going to tweak the 3.6k and the 910ohm resistor to bring the overall gain up so there isnt a drop in level.
seems to be a fair bit of noise which i need to look at if im going to use with my 100watt mesa but i dont know whether this is due to the fact that im using it through this fender champ diy amp!!!

 

[Spencerleehorton]

I’ve reboxed this original circuit univibe, I’ve put in several mods, speed mod, changed middle 1uf to 2.2uf and changed 4.7k resistors to 1.5k. Now it’s an acceptable fast speed and nice slow speed.
I’ve changed the 47k on the input (after the first 22k) to 2.2M and changed the 3.3k to 7.5k on the 3rd transistor collector and now have plenty of volume between effect on and off.
True bypass and I have also put in the 50k pot with 68k on each leg with the wiper going to the chorus/vibrato switch, taken out the two 100k resistors.

The problem I’m having is setting up the bulb and the LDR so that the effect is more prominent, on chorus it sounds nearly there depth wise but on vibrato on slow speeds the effect is really difficult to hear.
The other problem is I can hear the bulb, almost like there is an earth problem?
Any help on getting the effect more prominent and getting rid of the bulb noise would be appreciated!!

Here is a good link to schematics etc

https://musikding.de/docs/web/univibe-ForumVibe-final.pdf

 

[Spencerleehorton]

Just followed another layout schematic which is apparently from a original unit and wired the gnd as per that and it seems much quieter bulb noise wise now, just need to up the effect mix now as it’s still not enough effect.

 

[Spencerleehorton]

I’m also going to go through all the components as it must have sat in the shed for a good 15 + years so I’m sure some of the components may have gone out of spec, probably worth changing all the electrolytic right?

 

[Spencerleehorton]

All caps and resistors seem in spec, using bc109c for transistors which I will change for 2n5088 and use 2n3904 within the lamp driver .
I’ll document the transition from how it sounds now to hopefully a fully working how I want it too pedal.
The LDRs I have read should point upwards rather than straight at the lamp.
I’ve used a kinder suprise case to shield the lamp but does it have to be a metal case to shield it?

 

[soapy_goat]

I’ve used a kinder suprise case to shield the lamp but does it have to be a metal case to shield it?

can you share a pic, id like to see this? an effective shield must be conductive

 

[Spencerleehorton]

 

[Spencerleehorton]

The 50k pot on the left with the 68k resistors doesn’t really do much at the minute but I have noticed when hitting the chords hard there is a crackle and distortion so probably a bad transistor?

 

[soapy_goat]

my apologies, I was in EMI/RF shield mentality. the Kinder egg light shield is novel! i would start by going back through every component and ensuring I didn't place a resistor in the wrong spot and stuff like that. After my own errors are not to blame, then I start to suspect faulty part do you have a way to test the transistors out of circuit? may be time to invest in something like the PEAK DCA55. Maybe someone else has a cheaper option, there are Chinesium solutions that do more for less

 

[Spencerleehorton]

The originals used a metal light shield so I wondered whether this made any difference to noise or was just for the shiny internal faces so the light reflected off the insides?

 

[Spencerleehorton]

I think this maybe the original schematic?

 

[Spencerleehorton]

Here is another which maybe the same but has part numbers

 

[Spencerleehorton]

Here is a layout diagram

 

[Spencerleehorton]

im going to undo the volume mod ive done first, as it has been reported that this when played hard can cause distortion, so im hoping this is the problem.
will put everything back to stock and go from there.
i'll details the BC109C voltages and comapre with the 2N5088.
also ive found the capacitor values are slightly different on a original one.
C7 = 15nf
C9 = 220nf
C13 = 10nf
C16 = 6nf

will measure again but im pretty sure my C13 and C16 are not as per original.
i'll also put back the two 100k mix resistors
make a metal light shield and cover insides with shiny tape
R3 back to 47k got (2.2M)
R9 back to 3.3k, changed to 7.5k this i think is the distortion problem?
on the schematic the speed pot says 100KA, i think this is a miss print as its meant to be C100K stereo pot. other early original versions i think had a 250k?
i will check all resistors that i can, i couldnt find R48 (47k) on my pcb so may have to add or i may have just missed it?
R45 and R46 i have put 1.5k and happy with the speed of the LFO.
C20 is a 2.2uf
apprently R13,R19,R25,R31 4.7k can be adjusted to make the LDR work better so may put a trimmer here at some point to test?

Another thing i wanted to try was to have the transformer out of the case within a external PSU and just plug to a socket to save a bit of space within the case as i have got a SHIN- Ei pcb coming.

also there is this info:

AS = Amp Surgeon

1) C16 on AS's is a 0.006uf, on the manual schematic it's a 0.0047uf.
2) R37 on AS's is a 100K, on the manual schematic it's a 47K.
3) R45 on AS's is a 1.8K, on the manual schematic it's a 4.7K.
4) R46 on AS's is a 1.8K, on the manual schematic it's a 4.7K.
5) R47 on AS's is a 4.7K, on the manual schematic it's a 47K.

Amp_Surgeon's scheamtic vs. R.G. Keen's Neovibe -
1) C13 on AS's is a 0.01uf, on R.G.'s schematic it's a 470pf (C12).
2) C16 on AS's is a 0.006uf, on R.G.'s schematic it's a 0.0047uf (C15).
3) R5 on AS's is a 1M, on R.G.'s schematic it's a 1.2M (R7).
4) R37 on AS's is a 100K, on R.G.'s schematic it's a 47K (R37).
5) R49 on AS's is a 150r, on R.G's schematic it's a 68r (R48).

so far these are my findings.

 

[Spencerleehorton]

the other main reason for trying to detail all relative stuff for the univibe here is there is a growing number of resources disappering on the web!!
not saying im trying to out do anyone but for my own reasons of having the pedal and being able to dial in that "jimi sound"

 

[Spencerleehorton]

Seems that one of my problems could be R47 which on original schematic looks like it’s 47k but on all other schematics it’s 4.7k so will check this as this looks directly linked to the intensity control and maybe why the effect is so weak?

 

[dai h.]

hi,

J.C. Maillet's site used to have some interesting stuff (wayback machine) :

https://web.archive.org/web/20160402081752/http://lynx.net/~jc/pedalsUnivibe.html

(also FWIW (another bit apparently no longer on the site) I had this bit of text saved (not sure which exact page it was on) :

That Mojo Hendrix Throb

After building some WAH-shell Vibe clones in ’95 (including one for Keith Scott of Bryan Adam’s band) I posted my recipe on the internet and distributed the plans around ’98 … these early (de-coupled supply/ground + regulated audio) plans were copied by others shortly after

I recently started a private forum board dedicated to explaining the fine tuning techniques I used back then to get the best UNIVIBE sound possible … you can become a member by purchasing one of my Univibe+ PCB’s

Enter Mr. Dave Foreman, a dedicated Vibe enthusiast from Ohio … Sometime around July he contacted me about helping him tweak some of his DIY circuits … in my work forum he started off by posting the following:

… about a year ago I built up a Nxxvibe .. And I don’t think the throb is quite right.. Just haven’t been pleased with it.. So it’s been dormant until recently I decided to try to make it sound better.

here’s what Dave had to say recently:

Anyway, I’ll get to the present here, the first thing I did to the Nxx was replace the cells again, this time, pointing the cells towards the bulb, and i think since I destroyed the 25ma bulb, it got replaced with the 12v, 40ma bi-pin from smallbear, (I liked the way it looked,).. Bingo!…. Swirl was happening, I was happy, yay!!! But I was deluding myself, I STILL couldn’t get the throb I wanted, although I tried to convince myself I did… Now by this time this poor board turned into a Frankenstein board, pads and traces starting to peel, a few buss wire repairs required, etc..

Now enter, the bias offset mod, NOW we’re even closer… But STILL not quite.. Enter 24v supply.. Houston, we have success!!

JC had always said the the LFO and audio circuitry run better at a 24v, and as much as I didn’t realize the original ran at about that!! The moral here, 15V does not cut it, IMHO!!! Running at 24 seems to have opened up everything, INCLUDING what the Bias Offset does for the circuit!!

The recording here was made with my usual amp setup, my Si FF, (he definitely used an FF at Woodstock, not Axis circuit IMO).. So I’m very happy to say.. THIS is what i wanted.

-> Star/Spangle (mp3)

All Vibe PCB boards, whether mine or other copies, can be tweaked, or in some cases modded, to get the ultimate level of VIBE performance … details posted at the forum

source: http://www.viva-analog.com/

Also, this might be interesting (wayback machine link since the pics seem to be gone from the thread at the original site) :

https://web.archive.org/web/2014030...forum/chat/restoring-the-jimi-hendrix-univibe