Neovibe no signal, just 'whoosh-vibe' sound

[krisdoering]

OK, I built a neovibe based on RG's updated schmatic:  http://www.geofex.com/Article_Folders/univibe/vibeupdate.pdf

I used 2N3904s for all transistors.  The bypass works (of course), but there is no signal getting throught when the effect is engaged.  I can see the bulb pulsing and the speed and depth both affect the bulb.  Also, the volume changes the volume of the hiss/whoosh sound, which is vibey.  So, this would all lead me to belive that the pre-amp part of the circuit to be the culprit.

I took my voltages and I guess there is a problem with Q2, but though someone might see something jump out:

B+ at bridge:  +23.9

Q1
C  2.5
B  1.7
E  1.5
Q2
C  2.0
B  2.5
E  1.9
Q3
C  13.4
B  2.0
E  1.4
Q4
C  14.9
B  4.7
E  4.2
Q5
C  11.3
B  4.2
E  3.6
Q6
C  14.9
B  4.7
E  4.2
Q7
C  11.2
B  4.3
E  3.6
Q8
C  14.9
B  4.7
E  4.3
Q9
C  11.3
B  4.3
E  3.6
Q10
C  14.9
B  5.9
E  5.4
Q11
C  23.6
B  14-8
E  17-9
Q12
C  23.6
B  17-9
E  17-8
Driver tranny
C  23-19
B  8-3
E  3-0

Thanks for your help!

Kris

[R.G.]

You are correct, there's a problem with Q2, but that's just the symptom, not the cause.

Q1 does not have enough base bias (Vbe is only 0.2V) and that is letting too much current into the Q2 base, causing it to saturate and not pass audio. Of course, Q1 is not passing audio either, so they're both symptoms.

Check around Q1 for solder problems, wrong resistor value, etc. Also check the path to ground for Q1's base and emitter, as they go to the emitter circuits of Q3 and Q2.

[krisdoering]

Check around Q1 for solder problems, wrong resistor value, etc. Also check the path to ground for Q1's base and emitter, as they go to the emitter circuits of Q3 and Q2.

All of the resistances checked out, so I measured the emitter resistance to ground and it was about 30 Mohms.  It appears that I had a bit of a cold solder joint at the emitter of Q1.  It didn't look too bad...   

It is still a little noisy (like buzz sounds, not as loud as the guitar, and only at some settings).  I'll have to seal up the enclosure before worrying about that. 

Anyway, thanks for your help, RG!  Also, thanks for providing the resources to build it. 

Best Regards,
Kris

[R.G.]

That would do it. I hate the solder joints where the solder holds to the pad really well, and the flux will not penetrate the crust on some of my 40 year old resistors. The joints look good but as you note, they don't make contact.

I'm glad it's working. Yell if you run into more problems.

[krisdoering]

I sealed up the enclosure, and it seems to have sealed IN the noise.    I ran shielded cable from the input jack to the switch and from the switch to the output, and the ticking in time with the vibe is still there.  I guess I should run shielded cable to the board from the switch, too.  Is there a better way to keep the speed and depth noise away from the signal cables?  Should I try to shorten the speed and depth wires or coil a wire around them a la Fender silverface amps?

Thanks for any help... I should really post pictures and sound clips.  It's a nice sounding unit (without the noise).

Kris

[RedHouse]

That would do it. I hate the solder joints where the solder holds to the pad really well, and the flux will not penetrate the crust on some of my 40 year old resistors. The joints look good but as you note, they don't make contact.

I'm glad it's working. Yell if you run into more problems.

Got that!

I have one of those 100 drawer parts cabinets that I filled up with resistors back in the late 80's, and I too am experiencing the dreaded funky-lead disease on those old resistors. I only use them for prototyping as they are like 5% Carbon film types but I have found that I need to run a little piece of steel wool (#0000) over the leads and this soldering problem goes away.
(I give the steel wool a quick shot of automotive Brake Cleaner which knocks any oil residue off the steel wool)

It's a bit slow but I'm able to keep using-up the old resistors.

[R.G.]

I ran shielded cable from the input jack to the switch and from the switch to the output, and the ticking in time with the vibe is still there.

That's a little odd. I don't remember any previous issues with ticking to the LFO in the Neovibe. It's a mostly-sine-wave LFO, which produces almost no discontinuities to tick.

Did you use a pre-etched board, etch your own, vero, or perfboard?

What are you powering it from?

[krisdoering]

OK, I biased the bulb driver and moved some of the wires around, and it sounds a lot better.  I guess that tick wasn't a very good description.  It was more like a zzz ---- zzz ---- zzz ---- sound. 

Thanks for your help RG. 

Kris