neovibe problem

[alcoloic]

hi everybody
i just finished my neovibe and everything works and sound cool but there's still a big problem .
if i strum hard or if i use the humbucker it makes an awfull distorted gated sound .
i guess it's not a normal behaviour
for the moment i use  two 9v battery as power source .
all the parts meet the specifications exept a few resistors that are metal (the blue ones)
there's also a considerable hiss but that could be normal (i never used a real one)
if anybody have suggestions that would be great .
thanks in advance

[R.G.]

Hey! Here's  a thought.

That stickie thread at the top of the forum - you know, the one you actually have to consciously ignore?

The one titled "Debugging: what to do when it doesn't work?

I wonder if there's any help in there?

[alcoloic]

thanks a lot
i'm gonna try that

[alcoloic]

ok here's what i got

http://www.geofex.com/Article_Folders/univibe/vibeupdate.pdf

i get 14,9v out of the 78L15

Q1
C:2,1
B:0,9
E:1

Q2
C:4,3
B:2,1
E:1,5

Q3
C:11
B:4,3
E:3,7

Q4
C:14,9
B:4,2
E:4,3

Q5
C:11,2
B:4,3
E:3,7

Q6
C:14,9
B:4,2
E:4,3

Q7
C:11,2
B:4,3
E:3,7

Q8
C:14,9
B:4,3
E:4,3

Q9
C:11,2
B:4,3
E:3,7

Q10
C:14,9
B:5,4
E:5,5

Q11
C:16,5
B:3,1
E:it's hard to tell cause it change between 8 and 10,2

Q12
C:16,4
B:between 8 and 10,1
E:between 7,5 and 9,6

[alcoloic]

i forgot to mention that my guitar is active but i tried with another passive one and if i strum hard i get the same result

[rhdwave]

ok here's what i got

http://www.geofex.com/Article_Folders/univibe/vibeupdate.pdf

i get 14,9v out of the 78L15

Q1
C:2,1
B:0,9
E:1

Q2
C:4,3
B:2,1
E:1,5

Q3
C:11
B:4,3
E:3,7

Q4
C:14,9
B:4,2
E:4,3

Q5
C:11,2
B:4,3
E:3,7

Q6
C:14,9
B:4,2
E:4,3

Q7
C:11,2
B:4,3
E:3,7

Q8
C:14,9
B:4,3
E:4,3

Q9
C:11,2
B:4,3
E:3,7

Q10
C:14,9
B:5,4
E:5,5

Q11
C:16,5
B:3,1
E:it's hard to tell cause it change between 8 and 10,2

Q12
C:16,4
B:between 8 and 10,1
E:between 7,5 and 9,6

Ok, as far as i can tell you have multiple problems.  However, it's possible that as you start solving some this in turn will solve others.  One of the main things i've learned from debugging my neovibe builds through the generous help of R.G. and other kind individuals here as that for transistors the base needs to be between .5 and .7 higher than the emitter.  So, based on this simple rule you can see that several of your transistors are not adhering, namely Q1,4,6,8,and 10.  Q11 and Q12 may be off as well but they are known to be difficult to measure accurately so they may be ok.  I would start with Q1 and check all soldering in that area: that's all resistors and capacitors and traces...make sure that everything has continuity with your multimeter and make sure that there are no solder bridges.  Recheck with a magnifying glass.  You may just want to desolder and resolder any suspect components then remeasure your voltages. 

The other thing that i can see and i'm not an expert so i'm not sure if this really means anything is that you should be getting 15volts or more out of the 78L15.  I guess 14.9 maybe close enough...i don't know, but on the outside maybe it's an indication that your batteries are low...but i don't think that should effect the ratio of the readings on the transistors.

Good luck!!!

[R.G.]

Good advice, rhdwave. Those are the places to look, OK.

I think alcoloic may have an insensitive meter, too. The base-to-ground voltages on the Neo have been hard for some people to measure, and it's consistent with a low-input-impedance meter.

Alcoloic, can you remeasure the voltage from base to emitter, putting the leads directly on the base and emitter pins of Q1, 4, 6, 8 and 10?

I think the real problem is with Q10, but that's just a guess from too little info.

[Arno van der Heijden]

Could it be that this is just due to the use of active pickups? My Neovibe shows similar behaviour when I use a guitar with hot humbuckers.
I think the preamp of the Neovibe just doesn't have a lot of headroom.

[alcoloic]

thanks everybody for helping
i didn't found any shorts
here's what i get when i measure the voltage from base to emitter :
Q1 : 0,28
Q4 : 9
Q6 : 8,98
Q8 : 8,96
Q10 : 7,89
all the transistors are 2n5088
my meter is a cheap elix lx-830b so it's maybe not the best measurement tool

[rhdwave]

Something's wrong there...the difference between base and emitter from your readings on a couple of those is 7 to 9 volts? Are you sure you measured correctly?

[alcoloic]

i suppose, i've put the leads directly on the base and emitter like Mr R.G. told me .
i'm gonna give it a second try

[DeeBug]

I had the same problem.  I'll tell you what was causing my problem just on the off chance that the same thing is causing yours.  Having said that though, the chances might be slim that we both have the exact same cause.

In my case, the values of the C4 and C12 caps were wrong.  Instead of 330pF and 470pF polystyrene caps, I had put in 33pF and 47pF polystyrene caps (Mouser sent me the wrong values and I hadn't checked the them before soldering as I should have).  So, I took them out and put in 330pF and 470pF CERAMIC caps as I didn't have those values in polystyrene.  The problem was solved.  No more static with humbuckers.

But wait, there's more.

I wanted everything to be as perfect as could be so I eventually got the proper values in polystyrene and replaced the ceramics.  Problem returned!  Only this time it wasn't the values, it was just the type of capacitor.  It seems that all along the problem was with the polystyrene caps for some reason.  Could they have been damaged by soldering iron heat?  I don't know.  But after putting the ceramic caps back in, the problem was solved again. 

So, anyway, if you've got polystyrene caps in C4 and C12, you might want to check that out.  Good luck.

[alcoloic]

thanks for helping
i've checked and they're the right values and ceramic
i've also remeasured the voltages from base to emitter with the same results

[alcoloic]

i just noticed something really strange :
if i strum it start to hiss and make a sort of police siren noise in the background and if strum hard again those noises disappear !!!

[R.G.]

That's a classical description of parasitic oscillation going on. The hiss is heterodyned RF, the police siren is audio.

You have a power supply or wiring problem.

[alcoloic]

woaw thanks a million time R.G.
ok it was the crappy batteries i use ! i tried with some quality ones and that problem was gone
now i still have that distortion problem but maybe Arno van der Heijden is right and the neovibe just distort easily .
another question : the chorus is really subtle is that normal ?

[R.G.]

Wow, you're getting a good lesson! Crappy batteries = high power supply impedance -> oscillation. It's not often that the lesson is so clearly presented.

The input to the Univibe can distort under moderately high signal levels. As to whether this is normal or not - read the DC voltage on all the devices. Where one of them as too little headroom, it will distort. If they're all about correct, then it's "normal" for the circuit.

The Univibe is not a chorus - it's a phaser, and it's a phaser optimized for making vibrato, so it does not have the super phaser style sounds of other pedals  which are only phasers. IF your voltage don't show a problem AND it's otherwise OK, then it's probably that the two 100K mixing resistors need to be tweaked for deepest phasing.