Univibe non linearity

[fuzzman93]

Hi there,

I needs some help for debugging an old Univox univibe here's the story:

My old Univibe seems to have a problem.I bought this one a few years ago and since the begining ,the overall effect wasn't very strong ,especially for some notes on my guitar.
I tweak the pot ,modded the lfo to have the best effect but there's a big loss near 1kH .

I put it on my benchwork this afterternoon to solve the problem.I saw on my scope that the effect signal was ok for the low and the high notes but was weak for the middle band! I used an oscillator for the test and i saw that the level of the effect signal was near the same than the dry signal only from 20hz to 800hz and 3kh to 10kH.
I know that the four filters aren't working on the same frequencies so maybe one fliter doesn't work well.?The signal loss is present everywhere in the signal since i put my vibe on ,
but not in the bypass mode. If i set-up the light to display this loss, the effect isn't enough strong even with the intensity knob at full on .If i set up the light to have enough effect ,the loss reappears .
My microvibe sounds better than this vintage one!
I know that Univibes are all differents but i think for this case that it could be a malfunction
Any ideas ?
Cells ? Resistors? Trannies ? Caps? Lamp ? Supply ?


Thank you in advance
Bruno

[fuzzman93]

Univibe repaired!

Hi there,
No answers?,,no matter i have repaired my Univox vibe yesterday in the night.
Well First i opened the box ,i check all the 0.1uF caps ,they look OK
I measured the resistors ,i just verified if they are at 10 % or less they were not carbon comp type (last model producted by UNIVOX not Shein Ei)so the didn't drift a lot.
I've look trannies,they're OK too.Then i open the light can and i put a bit of black tape on three cell. I measure each cell with a 1kHz and 10kHz signal .I saw that all the cells had
different output level.The Univibe circuit have four differents caps for filtering.One of the cells appeared to lack some of the signal too much in the dark and two others have a bigger output signal.I open my benchwork light and it was the opposite .One the first cell i tested the signal didn't oscillate a lot,so i decided to try to change that,to have a better oscillation.
I change 0.1uF caps , 2 trannies nthing changed.
Many people are saying that Very precious cell's on Unibive are a big part of the sound,i'm not a collector,i'm musician and i prefer a good sounding device than a mint stock but crappy sounding vibe so i took a four cds cells in my component stock,changed the So precious vintage cells.I look at my scopemeter ,near the same results than before.
I decided to test if it's worse than before and i was very surprised that it was a nice lush chorus,not too wobbly,i try differnt speed,the effect was perfect,even at full speed or full intensity (more liquid and more organic sound),and the lack of frequencies i had before had completly disappeared.I compared with my microvibe,and now the Univibe was really better than the microvibe.i Try a small Breath from DSOTM,IT WAS IT! Same leslie effect with a little comb effect ,but i can ear now all the arpeggios clear sounding!
After that i took a look at the old cells ,they're not really the same than on the earlier models(Ref 5K for 2 and 5I for the two others)Univox put what the had in stock,i'm sure now it's because of that i had only paid 300$,it was one of the bad sounding Univibe .I took a lot of time (4 years ) because i was thinking that it was normal,but now i'm sure that it was not.The cells have to be matched!!Or maybe they have
drift with years.Vintage gear have always some mystery in them,it's because of that i like them too much!
Bruno Fuzzman