neovibe debugging - round two

[jeff g]

I completed the GGG Neovibe a few weeks ago, couldn't get it working and left it for awhile.  I've now rechecked everything and resoldered some pads.

The lamp works but still, no sound at all (bypass or effect)

In a recent post, Aharon asked about needing the bridge rectifier - I am using a Dunlop 18V wallwart and have hooked up the bridge rectifier. Is this correct?

I tried an audio probe - didn't get any sound anywhere on the board (only a loud hum).  I'm not exactly sure how to use the probe, but I had: guitar to input, nothing in the output and the probe to amp, ground and capacitor probe ??

Here are the voltages

T1
E 1.00
B 1.88
C 2.10
E/B -.49

T2
E 1.50
B 2.10
C 4.35
E/B - .57

T3
E 3.80
B 4.35
C 11.03
E/B -.60

T4
E 4.35
B 4.27
C 15.02
E/B -.43

T5
E 3.78
B 4.35
C 11.30
E/B -.60

T6
E 4.31
B 4.25
C 15.01
E/B -.44

T7
E 3.73
B 4.31
C 11.20
E/B -.60

T8
E 4.32
B 4.26
C 15.02
E/B 15.02

T9
E 3.75
B 4.35
C 11.20
E/B -.60

T10
E 5.52
B 5.42
C 15.02
E/B -.55

T11
E 8.10-10.20 (fluctuates)
B 3.06
C 16.73
E/B -.46

T12
E 8.05-9.79
B 8.1 - 10.1
C 16.72
E/B -.62

Lamp
E 1.50-2.10
B 2.15-2.70
C 16.72
E/B -.63

78L15
I 15.02
G 0
O 16.72

Thanks

[Aharon]

If you got an 18VAC wallwart you need the rectifier.
My doubt was if I was using DC,leaving the recto there would do any harm?.I don't think so,you may get another volt of so dropped,but I asked cause I'm not sure.
If you get a loud hum it may be a ground problem,check the input/output jacks and for solder blobs.
MAke sure the power jack is isolated.
Good luck.
I already started populating.
Aharon

[R.G.]

Those voltages look much better. The very low current transistors have base-emitter voltages of about 0.4 and a little over - that's what silicon does at tiny currents.

Your LFO is oscillating, which is good, that's a place that is a problem to lots of people.

To hook up your audio probe:

guitar to input jack
nothing on output jack
probe cable to amp

probe ground to effect signal ground
Probe capacitor to probe cable tip.

Before you do anything else, probe your guitar signal at the input jack. If that's miswired, you get nothing anywhere else. Once you verify that, probe each base starting at the input and working toward the output until you lose signal.

[Aharon]

I'm finding out it's a challenging build,tight board,small pads,100+ components.......not something that I want to rush.
I'm going to take a break.
Eyes red...........
Aharon

[jeff g]

well, i probed the input - no sound. then i noticed a had wired the switch vertically, not horizontally, so i rewired that.

checked again - no sound

so i rewired the input and output jacks - i'm assuming the the tips of both the in / out are supposed to go to the switch?

again - no sound (but i'm just using alligator clips on the jacks / switch until i verify what the correct connections are - could that be a problem?)

aharon - good advice on not rushing, but i've been working on this for over a month and i actually made the board bigger so i wouldn't have problems with tiny pads/ bridges etc. (guess that didn't really help !)

[R.G.]

so i rewired the input and output jacks - i'm assuming the the tips of both the in / out are supposed to go to the switch?
again - no sound (but i'm just using alligator clips on the jacks / switch until i verify what the correct connections are - could that be a problem?)

Just as a suggestion:
1. Momentarily ditch the output jack. You don't need it until the audio probe shows the rest of it is working.
2. Likewise, ditch the switch, same reason.
3. Wire an input jack onto the board directly. Verify with the audio probe that
  (a) you get audio at the jack. It's possible that you've been trying this with a bad cord from guitar to the jack.
  (b) you get audio on the board.
  (c) once you get there, you can probe the rest of the board.

It's reasonably likely that the problem is a wiring mistake, given your description.

Another way to test wiring is with an ohmmeter to verify what connects to what when the switch is flipped.

[jeff g]

To remove the switch and output jack, all I've got is pad A1 going to tip and pad B going to ring of input jack, right?

where does vol pot lug 2 go?

my audio probe doesn't seem to work - i used headphone cable, would that be a problem?

[Aharon]

Make sure that you ground the Volume pot to the output jack and do not connect any wires between the two jack grounds and if you have it in a metal box use plastic isolating jacks.
Try that,I think you have a ground problem.
Aharon

[jeff g]

i finally got the audio probe working - my test amp crapped out at some point !

i have sound at the input jack and up to the first transistor base, but there is a fairly loud hum.  there is audio at the output jack, but loud hum and scratchy noise

R1, R2 and R4 are ok at both ends,

R3 is ok at the input end, but there is nothing at the ground end (continuity to ground is Ok from R3)

R5 has no audio only a 'whoosh' sound

C1 is ok at both ends

C2 has no audio

It seems to me the problem is before Q1, but I can't figure out where.  I've resoldered Q1, Q2 and Q3 directly to the board (no sockets like the rest of the transistors).  I also resoldered R3.

Or maybe it's a grounding issue?

[Aharon]

Loud hum............looks like a ground loop.If you have a ground connection between the two jacks ........disconnect it.
Aharon