Neovibe mis-bias??

[wademalorgan]

Hello,
I recently built the neovibe.  After some messing with the lfo circuit I finally got the thing to vibe.  Sounds okay, it's just that when I would pick harder (mostly on the lower bass notes) you can hear a sort of gated distortion in the background.  Rolling back the guitar's volume pot a little seems to help with the gated overloading. 
I have a 250k pot mixing the phase stage and dry signal together.  When it's only dry signal I don't get the nasty overload.  it seems to be somewhere in the phase stages.  I did an audio probe and it seems to start at the first phase stage. I took some voltages of the transistors.  Looks like I have some problems:
V=16.96
Q1
c-2.30
b-.98
e-1.77

Q2
c-5.18
b-2.29
e-1.70

Q3
c-12.68
b-5.18
e-4.60

Q4
c-16.59
b-4.71
e-5.19

Q5
c-12.36
b-5.16
e-4.28

Q6
c-16.90
b-4.76
e-4.85

Q7
c-12.70
b-4.86
e-4.22

Q8
c-17.00
b-4.82
e-5.23

Q9
c-12.73
b-4.90
e-4.35

Q10
c-17.05
b-6.11
e-6.22

All the even numbered transistors (and the first one) seem to be mis-biased.  What is it that these mis-biased share within the circuit that would cause them all to be off, something that would make their emitter have higher voltages.  Any help would be greatly appreciated!  Thanks!
wademalorgan

[legomaniac4040]

I just finished my Neovibe about 2weeks ago, the only problem I had was the damn light bulb. The one from radioshack is really high, so my option was to remove as much plastic around base of bulb, drill hole thru board to lower bulb down and tap leads into trace underneath. I have pics in the buildyourownclone forum under neovibe. I matched my resistors as best could and built according to pdf file. I fortuantly didnt have any problems,sorry bout yours. Good luck in troubleshooting

[wademalorgan]

I just don't understand.  With these voltages it seems like no sound at all should pass, but yet I am getting a good vibe sound (sans the distortion in the phase stage).  it can't be that I have the trannies in the wrong way because then i would get no sound at all.
w

[R.G.]

I think you may have the naming on which pin is base and which is emitter messed up. Is that possible?

[wademalorgan]

I don't think so.  Base is the middle pin, right?

[QSQCaito]

2n5088


2n3904

[wademalorgan]

Thank you all for your help so far.  I double checked the voltages and they're still the same.  The base voltages on q1, q4, q6, q8, and q10 are lower than those of the emitters.  I'm very puzzled.  I double checked my parts placement, everything looks good as far as I can see.
w

[wademalorgan]

I did just notice that all my 1uf capacitors are only 25v and the parts list calls for 50v. Would this make a difference?

[legomaniac4040]

http://i77.photobucket.com/albums/j72/legomaniac4040/workingprototype011.jpg[img][/imghttp://i77.photobucket.com/albums/j72/legomaniac4040/workingprototype005.jpg]
Cap 4 on mine were the glass type 23ps133 yours arent, dont know if that can help.

[wademalorgan]

Okay, I used an ohm meter the resistance of the various resistors around the problem area.  I am just a little unsure if i'm doing it right.  I had the circuit unplugged from the power source. From the component side of the board I would touch one probe of the meter to a leg on the side of the resistor.  I would use the other probe and touch the other leg.  The readings would match up for the most part (4.7k resistors would read 4.7 on the meter, etc.)  except for resistors r14, r20, r26, r30, and r33.  I was expecting a reading of 100k from the meter for r14, 20, and 26 because they're all 100k however I got around    35kohm reading for all three.  r30 is a 68k resistor but got a 30.5kohm reading and r33 is a 47k resistor and only got a reading of 28kohms.       This has got to have something to do with these strange transistor voltages.  Are these readings the sign of faulty resistors? It seems like too big of a coincidence if they were all bad.  I don't know.  Sorry for being so long winded- I just spent a lot of time on it and would love to finally finish it.
Thanks!
wade
oh
here's the schematic: http://www.geofex.com/FX_images/vibeschm.pdf                                               

[legomaniac4040]

Wow, that does seem to coencidental. I built the exact same one and got lucky the first time for once.
Usually I am taking boards apart a few times to get it right. I hate to be the one to say this but you might have to start unsoldering and testing someof those componments when not in the circut. I have gotten some strange readings from time to time, Caps hold small charges and that might be giving you a false reading 

[slacker]

The readings would match up for the most part (4.7k resistors would read 4.7 on the meter, etc.)  except for resistors r14, r20, r26, r30, and r33.

You can't always measure resistances with resistors in a circuit because other things in the circuit are in parallel with resistors and that changes the value. To measure them you might need to unsolder one end of the resistor so that the rest of the circuit can't affect the measurement.

[John Lyons]

The voltage of the 1uf caps are fine at 25v rating.
Check the color codes first on the resistors and make sure everything looks right. You may have to check them later by lifting one leg and measuring them.
Make a fresh copy of the layout and use a colored pen to mark off each component on the board as you check them.
Use the voltage chart in the PDF and make sure you have close to those voltages on your build. Measure red probe to ground and black probe to a ground point at the in or output jack.
Search in the forum here for neovibe voltages and there should be some voltages posted. Compare these to what you have now.
Get a loupe or strong magnifing glass and make sure that you have no solder bridges and that the flux is cleaned off the bottom of the board and in between traces and solder pads.
I print out a reversed PCB pattern to check for solder bridges. The pattern should match the bottom of the board.

John

[R.G.]

The reason I haven't said more on this one is that I'm still thinking.

If there are no mistakes in measurement or pinout, I'm not sure how any sound is getting through it at all. Yet, it is most of the time. Then there's the issue of it only gating on loud, low bass notes. Bizarre.

That looks like my layout. Did you make it yourself or get it from GGG, my licensed source? That would tell us whether to worry more about PCB pattern or construction. JD's PCBs are pretty well made.

[wademalorgan]

Yeah it's really weird.
I made the pcb myself with your layout so maybe that's the problem.  Like I said before, it sounds great if you don't hit the low e or a hard or if you turn your guitar down a little bit.  Arggg.
Thanks for the input!
wade

[yunger]

wade, did you find the source of the problem? i have almost exactly the same problem. the emitter voltage is greater than the base voltage on q1, q4,q6,q8 and q10 on my neovibe. if it wasn't for q1 being weird i would suspect the ldr's.

[Arno van der Heijden]

I'm sorry for replying to this old thread, but I'm having exactly the same problem with my newly built Neovibe... 

So, did anyone find the source for this problem already?
The weird thing is that it sounds pretty good as is.... the only problem is that it seems to clip with higher output pickups. I'm at a loss.... 

BTW, I etched the board myself and used 2N5088's. If required I can post the measured voltages...

[Arno van der Heijden]

bump

[Arno van der Heijden]

bump

[Solidhex]

I posted in a different Neovibe thread but I'm also having problems with the biasing on Q1,Q4,Q6,Q8, and Q10. The emitters are only .30 to .4 V's below the base not the reccommended .6 to .7

--Brad