Neovibe Debug Help

[lonewolf]

you should not get sparks probing M or N..that is the dry and wet output .check for a dc voltage from M to ground..if there is a dc voltage you have a problem..check C 18 and make sure it is correctly installed...if you have leaking dc that will cause a hum.. also check C16-17

[tr1p1n]

you should not get sparks probing M or N..that is the dry and wet output .check for a dc voltage from M to ground..if there is a dc voltage you have a problem..check C 18 and make sure it is correctly installed...if you have leaking dc that will cause a hum.. also check C16-17

For pad N I get 0V, also for pad M to ground there is no voltage.

C18 is installed correctly.
+ = 1263mV
- = 002 - 006mV

C17
+ = 5.5V
- = 0V - 001mV

C16
+ = 5.5V
- = 6.23V <--- This can't be correct, right?

[lonewolf]

the positive side of C17 and the neg side of C16 connect to the emitter of Q 10 which should have a voltage of approx 5.4v dc so that is right

[tr1p1n]

the positive side of C17 and the neg side of C16 connect to the emitter of Q 10 which should have a voltage of approx 5.4v dc so that is right

Oh, well thanks, one thing I didn't have to worry about. As for the audio probe, it's OK if I use a polarized cap? not going to damage anything?

[lonewolf]

I think you want a polarized cap to block dc..I have never used a audio probe...I have only used a dvom and a magnifier and my eyes to look for opens/shorts/cold joints..etc

[R.G.]

As for the oscillation its like a low bass hum, gets louder when increasing the depth and faster with the speed pot. Am I not supposed to hear the oscillation?

No, you're not supposed to hear it. This is consistent with the signal path being open somewhere in the audio chain, and power line mains hum being modulated by the phase shift line.

mind you I do have the light shield off, if that has any correlation.

No, it has none with the hum you hear.

Switching power supply? Well I'm powering this with a 24V DC/100ma wall wart plugged into a power strip.

The wart may be switching or non switching. So we don't know yet. Anyway, a switcher would not do the bass hum you hear. It MIGHT do the low bass hum if it's unfiltered, but the big filters on the Neovibe board should prevent that. We still don't know.

Now about the audio probe, was using the 1uf 50v from the specified parts list for this project, is that OK? I mean it works but when I began to probe, figured I'd do the pads first, A1 works of course. Skipped over to N & M, both get a signal but I got a little frightened when M sparked and the light went out. I'm not sure if this was the cap or the fact that the wire isn't soldered all the way to the board and the sparks came from the exposed wire(probing top side).

1uF is big enough to cause some minor sparking when it's suddenly connected to a point with DC on it, or especially if it has been charged up to some voltage by reading some point with DC on it and you then connect it to another point. The sudden difference in voltages might cause minor sparking. Ignore it or use a 0.1uF cap.

Regardless we still have signal, the light still oscillates, but it did scare me enough to put a halt to probing and instead move on to measuring voltages (which isn't any better, for me at least).

If you're concerned, unplug the wall wart before moving the probe to the next point, then turn the power back on. I think you have an open audio path, and the probe will find it.

This is how I went about this to avoid any confusion. R13 - 4.1V =  4.5V (what I get).

Do you mean that R13 is supposed to be 4.1V and you read 4.5?
Correct me if that's wrong. I'll assume that it is and forge ahead.

All points that say to 15V source = 14.78V
R13 - 4.1V = 4.5V
R18 - 10.9V = 11.35V
Q5 - 4.1V = 3.35V
R32 - 6.1V = 6.04V
Q10 - 5.4V = 5.5V
R40 - 11.7V = 15.95V
Q12 - 10V = 11.6 - 16V (Goes from 11.6 to 12 something, 14 something then finally 16 before it repeats itself)
C25 - >17V = 27.2V

Nothing in that is wrong enough to cause the problems you're describing.

It would be more helpful to have both the DC voltages (as one set of test data) and a listen with the audio probe at each of these points:
- the input pad
- collector and emitter (both!) of Q3
- base of Q4, both collector and emitter of Q5
- base of Q6, collector and emitter of Q7
- base of Q8, collector and emitter of Q9
- base and emitter of Q10
- pads N and M

As for the audio probe, it's OK if I use a polarized cap? not going to damage anything?

It's OK to use polarized, but that forces you to get the polarity right. In this case, all the places you'll connect it will have a positive voltage with respect to ground (where you'll hook the ground clip on the audio probe) so the + side has to be the one that probes the circuit, the (-) side goes to the jack/cord/amplifier.

I think you want a polarized cap to block dc..

All caps block DC less than their specified voltage. Polarized caps only block it in the specified direction. Non-polarized caps block it both ways.

[tr1p1n]

Yeah you got it right for how I labeled the voltages, but the one voltage where its supposed to be 11.7V and I get 15.9V, thats OK? As for the audio it stops at collector & emitter of Q3. Went on to Q4 and nothing, so I just stopped assuming if the signal didn't make it to Q3 it won't make it any where's else. And when you said collector & emitter of Q5,7,9 and 10, I should touch them both too, right? Some you said clearly both others its this and that, so kinda confused. Also, could flux residue block DC or signals from traveling the traces? Would Isopropyl alcohol 91% be OK to clean this PCB?

[R.G.]

Yeah you got it right for how I labeled the voltages, but the one voltage where its supposed to be 11.7V and I get 15.9V, thats OK?

At least that's not what's keeping it from passing audio. Your board has had multiple problems. We'll run them all down, perhaps one at a time.

As for the audio it stops at collector & emitter of Q3. Went on to Q4 and nothing, so I just stopped assuming if the signal didn't make it to Q3 it won't make it any where's else.

Well, that's at least one thing I was trying to find out. So let me be sure I understand: you found audio at collector of Q3 and at the emitter of Q3, but not at the base of Q4, right?

Although this is probably what we wanted to know, stopping before you get all the data means we have less information that we would otherwise have. As you note below, the contact at base of Q4 might be bad with the audio probe. If you then found audio at Q5 collector and emitter, we would know it had made it through Q4 by looking at the schematic. It's a system of self checking. If you quit looking at the first odd measurement, you are more prone to errors in the process of measuring, and have no way to check yourself. You're right - this is a teaching suggestion to you and an ever-so-faint criticism. You'll need to remember this if you keep on with audio electronics. Don't quit checking before you have all the data.

And when you said collector & emitter of Q5,7,9 and 10, I should touch them both too, right? Some you said clearly both others its this and that, so kinda confused.

It was a little ambiguous. But yes, check both emitter and collector of Q5, 7, 9, and 10.

Also, could flux residue block DC or signals from traveling the traces?

No. But it could well prevent your capacitor-lead audio probe from making good contact with the traces and give you a false no-audio-found. The signal would still be in the trace, traveling down it, but your probe would not make contact with the trace. This kind of thing could lead to the measurement error I mentioned above.

Would Isopropyl alcohol 91% be OK to clean this PCB?

Yes. Toothbrush and rubbing alcohol, remembering that alcohol is only slightly less flammable than gasoline at high concentrations, like 91%, and that alcohol vapor is a flammable gas. If you decide to do this, do it in a well-ventilated place, far away from all sources of ignition.

If you found audio at Q3 emitter and collector, and no audio at Q4 base (and that no-audio-found was a valid reading) then it solidifies my suspicion that there is a break in the audio path. In this case, it means that there is a break between collector of Q3 through Q5 to the base of Q4 *and also* a break from Q3 emitter through C6, the LDR, and R15 to the base of Q4.

It's really, really good practice to repeat the measurement that finds a circuit fault several times to keep false positive errors from confusing you.

[tr1p1n]

What I meant (at first) was I couldn't get audio at Q3, then I moved onto Q4 then gave up thinking if audio wouldn't make it there, why would it go here. This whole thing was a mistake on my part, after reading what you wrote I decided to go back and re-check. The way I was doing it before was with my amp on and no headphones, so when I first got to A1 it was LOUD, not to mention just touching the probe makes this loud thumping noise. So I turned my amp down being the reason why I couldn't hear the audio on anything else, when re-checking I eventually found I could hear the audio when turning the amp up. So I got my practice amp, plugged in some headphones and turned it all the way up, while trying to not go deaf at the same time. But the audio passes all the points you asked me to check, once again it was my mistake and I'm sorry about that. So now the question is, where do I go from here?

[R.G.]

What I meant (at first) was I couldn't get audio at Q3, then I moved onto Q4 then gave up thinking if audio wouldn't make it there, why would it go here.

Ah. OK. That helps.

This whole thing was a mistake on my part, after reading what you wrote I decided to go back and re-check. The way I was doing it before was with my amp on and no headphones, so when I first got to A1 it was LOUD, not to mention just touching the probe makes this loud thumping noise.

No problem. We'll get there. The loud thumping is to be expected. You're connecting a guitar amp input to places with several volts of DC on them. It's going to thump, that's to be expected.

I'm not clear why your headphones are less loud than the amp itself if you have them on your head.

The audio at A1 should be your reference loudness. There is not much gain in this circuit at all. The signal at Q3 collector and emitter and all the other points along the way may be a bit louder than A1, but not subjectively twice as loud, as a guess.

when re-checking I eventually found I could hear the audio when turning the amp up. So I got my practice amp, plugged in some headphones and turned it all the way up, while trying to not go deaf at the same time. But the audio passes all the points you asked me to check

Hmmm. So you get audio all along the phase line, Q4 through Q10 emitter, right? About the same loudness all along the way? Any variation in loudness?

[tr1p1n]

What I meant (at first) was I couldn't get audio at Q3, then I moved onto Q4 then gave up thinking if audio wouldn't make it there, why would it go here.

Ah. OK. That helps.

This whole thing was a mistake on my part, after reading what you wrote I decided to go back and re-check. The way I was doing it before was with my amp on and no headphones, so when I first got to A1 it was LOUD, not to mention just touching the probe makes this loud thumping noise.

No problem. We'll get there. The loud thumping is to be expected. You're connecting a guitar amp input to places with several volts of DC on them. It's going to thump, that's to be expected.

I'm not clear why your headphones are less loud than the amp itself if you have them on your head.

The audio at A1 should be your reference loudness. There is not much gain in this circuit at all. The signal at Q3 collector and emitter and all the other points along the way may be a bit louder than A1, but not subjectively twice as loud, as a guess.

when re-checking I eventually found I could hear the audio when turning the amp up. So I got my practice amp, plugged in some headphones and turned it all the way up, while trying to not go deaf at the same time. But the audio passes all the points you asked me to check

Hmmm. So you get audio all along the phase line, Q4 through Q10 emitter, right? About the same loudness all along the way? Any variation in loudness?

The headphones weren't less loud, Well let me try an explain the situation better. It was the fact that my normal amp couldn't be at a decent level to hear the signals (people here were sleeping and work extremely early). I mean the thumping sounded like thunder but the signal was like 1/10th of that. So for example the volume on 1 sounded like a decent by yourself guitar level, not obnoxiously loud and it wasn't to soft. But for me to hear the signal, it was at say 6? which is LOUD, so the thumping thunder was insanely loud but the song I was pumping through sounded like volume 1. So when I went back to re-check I was like oh well, lets just crank this and get it over with. And that's when I heard the signal at Q3, so I then proceeded use my little tiny practice amp that has a headphones jack to listen, which was loud enough it self to make my headphones crackle. So all the collector and emitter ones you told me to check are like half the volume of A1, but if I were to touch just the collector or the emitter it was the same, if not a little louder. And another thing I noticed when using my little amp with headphones is, not only can I hear the oscillation, but the clean guitar signal I was talking about kinda throb's/wobbles to it. Its like the effect want's to work but then again it isn't working and another thing I didn't mention before was when I do press the DPDT to go from bypassed to effect it cuts the volume down by 90%, almost to nothing. I thought at first it was the volume mod, according to the GGG files I did backwards or something (probably wouldn't matter anyways) but I have them right. No idea what's going on but one last question, as for the audio signal its supposed to stop at the LDR's right? then from the bulb down on the schematic just alters the above audio signal right? Was curios to probe there but didn't hear anything but on the bulb, the oscillation sounds pretty crazy.

[R.G.]

The headphones weren't less loud, ... So all the collector and emitter ones you told me to check are like half the volume of A1, but if I were to touch just the collector or the emitter it was the same, if not a little louder.

OK, so the volumes are not dramatically different. That's probably OK for this stage of debugging. Signal completely missing is not good.

And another thing I noticed when using my little amp with headphones is, not only can I hear the oscillation, but the clean guitar signal I was talking about kinda throb's/wobbles to it. Its like the effect want's to work but then again it isn't working

"Throbs/wobbles" is what it is supposed to be doing at that point. So the audio processing is doing what it is supposed to be doing, albeit maybe with some input/output volume problems. This is a Very Good Thing for you, because it tells you that the circuit board is doing mostly what it should be doing. The signal could not throb/wobble without both the audio section and the low frequency oscillator working, as well as the bulb and LDRs.

and another thing I didn't mention before was when I do press the DPDT to go from bypassed to effect it cuts the volume down by 90%, almost to nothing. I thought at first it was the volume mod, according to the GGG files I did backwards or something (probably wouldn't matter anyways) but I have them right.

And this suggests a wiring problem.

No idea what's going on but one last question, as for the audio signal its supposed to stop at the LDR's right? then from the bulb down on the schematic just alters the above audio signal right? Was curios to probe there but didn't hear anything but on the bulb, the oscillation sounds pretty crazy.

That is right. There is no audio supposed to be in the bulb on down in the schematic.

From here, the audio probe and some careful work on the wiring is the next step. I recommend printing a fresh copy of the wiring diagram, then tracing wires on the actual unit and marking them off with a colored marker on the diagram one at a time. Be especially careful with whether the signal and ground are reversed on the input and output jacks. I've made this mistake before myself.

[tr1p1n]

Well unless there's some specific way to wire the DPDT, I mean as in if there's a certain way you hold it then the wiring is OK, I think. I switched the input/output jack wires around just to be sure, one way is clean bypass with barely any volume on effect, other way is loud crackling on bypass and just loud crackling in effect. So I assume I got that wired correctly (wired with the clean bypass) And as for the speed/depth they both behave the way they should and the volume works fine when the effect is on. The chorus/vibrato shouldn't be to hard to mess up, middle wire goes to volume and the two opposite ones I don't think really matter which side is chorus and which side is vibrato. No idea what's going on, just have to crank the amp all the way to hear anything and as for the throbbing I think I kind have described it the wrong way. It doesn't seem like the effect it should be, it just cuts the signal on and off in unison with the bulb. Unless that's exactly how it's supposed to work, just doesn't seem like a uni-vibe (yet).

[R.G.]

Well unless there's some specific way to wire the DPDT, I mean as in if there's a certain way you hold it then the wiring is OK, I think.

Actually, there is. I recommend you UN wire the DPDT and test again. Just wire the input to the input jack, the output to the output jack.

[tr1p1n]

OK but nothing still, no bypass, no effect. And you meant input/output wiring as just wire them to the DPDT's input/output? Silly question but I want to make sure I got this right. But as for a specific way, I mean it's just 6 lugs, 3 on each side so it's either have it right side up or upside down? Or did I get the wrong switch? Mouser part# 633-EB2085-RO

[R.G.]

OK but nothing still, no bypass, no effect. And you meant input/output wiring as just wire them to the DPDT's input/output?

I meant:
Locate the wire from the input jack tip connection to the DPDT. Unsolder it from the jack.
Locate the wire from your input pad on the PCB - I believe you're using A1. Unsolder this wire from the DPDT.
The wire from A1 that you just unsoldered on the DPDT end - solder THAT to the input jack tip connection.
Check to be sure that the wire from the sleeve connection of the input jack still goes to the input ground pad on the PCB.
Locate the wire from the output jack tip connection to the DPDT. Unsolder it from the output jack.
Locate the wire from pads N and M. Unsolder them from the chorus/vibrato switch.
Leave the wire from M unconnected. Solder the wire from pad N to the tip connection of the output jack.
Check to be sure that the sleeve connection on the output jack still makes connection to the circuit board ground (perhaps by using your multimeter set to ohms to see if you detect a near-zero resistance between the sleeves of the input and output jacks.)

Now repeat the audio probe tests, but include the tip connections on the input and output jacks to the points to listen, as well as pad M.
Report the relative audio levels from input jack through the output jack, including the previously tested transistor points.

[tr1p1n]

As for the sleeve to ground connection, I can get it to say 0.01 (lowest for my meter) but soon after it goes to 6.6. Maybe it just me or my meter, not sure.
For the tests when I say OK it means the base/reference volume of the Input and of course 1/2 the volume being exactly that, half of the reference.
Input-OK
Output-OK
Pad A1-OK
Collector & Emitter Q3-OK
Base of Q4-OK
Collector & Emitter Q5- 1/2 the volume
Base of Q6-OK
Collector & Emitter Q7- 1/2 the volume
Base of Q8-OK
Collector & Emitter Q9- 1/2 the volume
Base & Emitter Q10-OK
Pad N- OK
Pad M- OK

[R.G.]

Your audio path is doing OK, you have a wiring problem.

[tr1p1n]

Your audio path is doing OK, you have a wiring problem.

Everything is wired OK. Volume, Depth, Speed knobs are working perfectly, I don't see how I could mess up the DPDT and the jacks I'm pretty sure are correct also. Even changed A1 to A and same thing. On switching to effect volume is cut down by 90% if not more.. No idea what to do.

[Jdansti]

Can you post a clear photo of the current wiring showing all of the off board components and how they are wired?