Another Neovibe debug.....noooooo!

[axg20202]

Haha, well, my Prebuild Questions thread has lead to this one, sadly. The lamp doesn't even light up and there's definitely a problem with the tranny biasing somewhere. So, if anyone can help, particularly you RG, that would be great.  I think the problem could be with Q11 amd Q12. Here goes:

Latest GGG layout - I made the board.

Parts different from layout:
C5 = 12nf instead of the 15nf required (didn't have one - is this a problem?)
R42 and R43 = 2.4k (speed mod)
R49 = 47k (lamp swing damping mod)
R8 = 910R and R9 = 3.6k (unity gain mod)
TR1 = 500R

(yes, I know I should have used all stock values first...I have roundly whipped myself for being too keen to tweak the circuit with common mods before getting it working....I know, I should be shot!).

All Q's = 2N5088 except the lamp driver which is TIP-120

Now for some readings:

Input voltage: 20v DC
BB102 +ive =  17.5v

7815:
I = 17.5v
G = 0v
O = 14.1v


TIP120:
B = 3v
C = 17.4v
E = 2.1v

Q1:
C = 1.9v
B = 0.8v
E = 0.8v

Q2:
C = 3.4v
B = 1.9v
E = 1.3v

Q3:
C = 9.8v
B = 3.4v
E = 2.9v

Q4:
C = 14v
B = 4v
E = 4.5v

Q5:
C = 10.2v
B = 4.5v
E = 3.6v

Q6:
C = 14.1v
B = 4v
E = 4.7v

Q7:
C = 10.4v
B = 4.7v
E = 4v

Q8:
C = 14.1v
B = 4v
E = 4.4v

Q9:
C = 10.3v
B = 4.4v
E = 3.7v

Q10:
C = 14.1v
B = 5.1v
E = 5.2v

Q11:
C = 17.5v
B = 3.3v
E = 9.6 - 9.9v

Q12:
C = 17.5v
B = 9.9v
E = 9.1v


If someone can help see some sense from these that would be cool. RG? Care to save the day?....again!

Thanks,

Andy.

[R.G.]

Input voltage: 20v DC
BB102 +ive =  17.5v

7815:
I = 17.5v
G = 0v
O = 14.1v

Your 15V regulator is being starved for voltage. That's why the output is 14.1 instead of 15. With 20V in, if you left the bridge rectifier on the board, that would eat 1.4V, leaving 18.6. I'm not sure why you lose another volt between the bridge rectifer and the regulator, or why the regulator is not working OK on 2.5V. But this is an aside. The circuit will run on 14.1V.

Q1:
C = 1.9v
B = 0.8v
E = 0.8v

If you measured correctly, this is a good reason you get no sound through. The base and emitter of an NPN must be 0.5 to 0.7V apart, no more, no less. With base and emitter at the same voltage, it's likely that they're shorted somehow. Make sure the measurement is correct, then track down why the base and emitter are at the same voltage.

Q2:
C = 3.4v
B = 1.9v
E = 1.3v

Looks OK.

Q3:
C = 9.8v
B = 3.4v
E = 2.9v

Looks OK.

Q4:
C = 14v
B = 4v
E = 4.5v

Emitter higher than base? Did you get the base and emitter voltages mixed up? If the emitter is really higher than the base, this transistor will not pass audio. What is pulling the emitter too high?

Q5:
C = 10.2v
B = 4.5v
E = 3.6v

Emitter lower than the base by 0.9V? Should not be that far.

Q6:
C = 14.1v
B = 4v
E = 4.7v

Emitter higher than base? Measurement mixup or real problem?

Q7:
C = 10.4v
B = 4.7v
E = 4v

I believe this one - base is 0.7V higher than the emitter.

Q8:
C = 14.1v
B = 4v
E = 4.4v

Again base too low.

Q9:
C = 10.3v
B = 4.4v
E = 3.7v

and base too high, by a bit.

Q10:
C = 14.1v
B = 5.1v
E = 5.2v

Same.

Q11:
C = 17.5v
B = 3.3v
E = 9.6 - 9.9v

It turns out to be remarkably hard to measure the base voltage of Q11. Measure the voltage on the other end of that 2.2M resistor that's attached to it. Your meter (and mine, too!) will load down the measurement.

Q12:
C = 17.5v
B = 9.9v
E = 9.1v

Looks OK.

Summing up: You may have some measurement issues, just guessing. Check the pinouts and be sure you're measuring the correct pins. Also check your measurement scale. Use a 20V scale if you have it available. And really look into that problem with base and emitter equal voltages on the board.

[axg20202]

Thanks RG - I'm pretty sure I measured correctly but will make them again, including your suggestion for Q11, and post again. Thanks for helping out (and providing the circuit).

If the orientation on the board for the 5088s is the same throughout, I don't think any are incorrectly installed. I should point out that I have socketed all tranny positions because of the nightmares I had read with biasing them. I want to do as few solders and resolders of pads as possible.

As for the recitifier voltages, the strange thing is - I think that when my power source was set yo 18v, I was getting 15v on the circuit. I should probably look into this and  consider changing it back to 18v input, but for the purposes of the debug I might keep it as is to avoid confusion.

[R.G.]

Another thing to look for is that since you made your own circuit board, you may have tiny thread-shorts between lands. Go over it with a magnifying glass, especially around Q1.

[axg20202]

How strange! I was just thinking about where I could buy a magnifying glass from on the way home!

Thanks a million.

Andy.

[axg20202]

Well, I'm happy to report that I'm up and vibing! Like another person on this forum though, the transistor voltage readings I'm getting suggest it shouldn't be working. After checking over all traces with a magnifying glass, finding nothing untoward, scraping around the transistor pads for good measure, I was getting the same readings as before and still no lit bulb. I was about to go and post the new readings and a further plea for help, but something made me crank the lamp driver trim pot up full tilt and bang.....then there was light! The optimum dim orange glow (lamp barely lit) with depth at minumum is only possible on my vibe when I crank the 500R trimmer fully clockwise. After positioning the LDRs abit, I plugged it into an amp for the first time and all is working well. I might fiddle with the LDRs some more to optimise it a bit but this thing is killer!

I would like to know why the tranny bias readings seem to be toally off, but it sounds like a Univibe to my ears so I'm caring less and less with each chord played through this thing. It is a bit on the 'tremolo' side of vibey, which I would like to reduce a bit to a more wavey sound (work with me here!), but I'm on my way with her and that's what counts.

Meanwhile, RG, you are a scholar and a gent for sharing this circuit and taking the time to help people like me get it to work. In this case, I suspect it was working all along, but the voltage readings were sending me on a wild goose chase. In any case, thanks very much for your input, which encouraged me to have a good poke around.

Andy.

[R.G.]

My pleasure.

I think there is something in the human psyche that has a yearning, a poorly understood longing for wild geese, given the ease with which all of us go off chasing them. Me especially.

[albatross]

Ive built mine, and having problems..

trimmer works, and bulb blinks but no vibe..
chorus vibe switch turns off signal on one side.

And now the voltage regulator is smoking!


Ive checked for bad traces, now ill check volages after ive replaced the regulator.

[albatross]

seems like my guess was wrong in this post http://www.diystompboxes.com/smfforum/index.php?topic=55638.0 for this Pinout

I measured as is, and i got :

IN - 27
gnd - 0
out - 27

Swapped it round and now i get :

in - 27-28
gnd  - 0
out - 15.1

I am using a ElectroHarmonix 24vdc transformer

A quick look at the voltage references on the schematic, and mine are wrong...

c25 28

q12 e 24.6

r40 - 27.7

i didnt go any further as something is defo wrong here..

the 2 1000uF caps i used for c24 and 25 are only rated at 25v....