neovibe. agonisingly close !!

[1878]

Hello Everyone.

I built a Neovibe yesterday & everything seems to work, bulb dims, speeds up etc. I get signal in bypass, but when engaged, I get chorus & vibrato, but very quiet & distorted. I've audio probed it & can't seem to find any specific point where signal drops & becomes distorted.

I measured the voltage going in at 22vdc. Seeing as the bulb part works as it should, where would be the best area to start measuring voltages ??

Thanks.

[R.G.]

As noted in "what to do when it doesn't work", that sticky at the top of the page that everyone has to ignore to get down to the active discussions, measure the pin voltages on all transistors.

With that as a goal, where you start is immaterial.

[1878]

Okidoki...

I'm struggling for time at the moment due to a 3 y.o with a head cold. I've used the readings on page 6 of this document...

http://www.generalguitargadgets.com/pdf/univibeupdate.pdf

as a guide. These are the readings I have.

19.9vdc at the power jack.

base of Q4: 1.43v should be 4.1v

collector of Q5: 4.4v should be 10.9v
emitter of Q5: 0.62v should be 4.1v

base of Q10: 1.83v should be 6.1v
emitter of Q10: 1.5v should be 5.4v

point between R40 & R41: 11.3v should be 11.7v

emitter of Q12: consistently alternates between 12.3v & 8.5v

positive side of C25: 19.1v should be 17v

I'll get the CBE readings for all transistors as soon as I have more time, but I hope this is enough for peeps to be getting on with.

Thanks again.

[PRR]

Get the kid healthy and happy first.

> collector of Q5: 4.4v should be 10.9v
> emitter of Q5: 0.62v should be 4.1v

Wrong part-value or transistor pinout. (The C reading says current is too high, but the E reading says current is too low, so something aint what it's supposed to be.)

Since this is a "signal" problem, I would also be wondering about Q1-Q3, the signal input amplifier. Ah, the party-colored GGG PDF shows no voltages?? By inspection, Q3 and its resistors should be splitting the supply voltage roughly 1:1:1 or 1:2:1. So 5V at E and 10V at C, or 4V at E and 11V at C, something like that. "Cathodynes" can often work considerably off their nominal proportions; this one has considerable gain and is trying to get two outputs from one stage, so it probably can't be happy if very far from my guesses.

[1878]

Thanks for the reply. My little boy is much better now too thanks. He's currently 'helping' me with the shed.

I've just taken voltages on all transistors & something started to dawn on me whilst doing it. I checked out my hunch & I was correct. I've used a 7805 instead of a 7815 !?!?

I can get either one of these tomorrow...

http://www.maplin.co.uk/p/l78s15cv-2a-positive-fixed-voltage-regulator-uj57m

http://www.maplin.co.uk/p/ts7815cz-1a-positive-fixed-voltage-regulator-to220-case-ql33l

Would either one be suitable ?

Thanks again.

[duck_arse]

both those parts are 15V regs, one slightly higher current rated, your answer is probably 'yes'. but you'd check your datasheets, just to prove me wrong, wouldn't you?

[1878]

No. I wouldn't have a clue even after reading a datasheet !!

[Cozybuilder]

The GEO Neovibe parts list specifies Mouser 511-L7815ACV, which is a 1.5A rating.

Of the two you listed, the first one is 2A, the second one 1A. While both are the same size (TO 220 package), I'd go for the 2A.

[1878]

Funnily enough, I've just found some 78L15's in a TO92 package in my bits box. I've fitted one & now rather than being very quiet & distorted, it's now slightly louder & distorted. These are rated at 100ma though. I'll get the 2a rated version tomorrow & report back.

Thanks again.

[PRR]

> used a 7805 instead of a 7815

It is good to check all major supply voltages. You did give the main 19V, but that's stepped-down to "15V", which is actually 5V in your build. Which explains the way-off voltages on Q5 (I shudda thot of that).

This plan does not need a big 2A regulator. Your jellybean-size reg should be fine.

Positive side of C26, "+15V Source", goes to a lot of resistors in the audio portion. Should now be near 15V. If not, a wiring mistake is more likely than a too-small regulator.

[1878]

Taken new readings for all transistors. All readings are C B E...

18vdc at power jack

Q1
2.48
0.89
1.43

Q2
1.96
2.48
1.90

Q3
14.9
1.96
1.47

Q4
15.00
4.30
4.35

Q5
11.2
4.30
3.75

Q6
15.00
4.26
4.35

Q7
11.29
4.33
3.71

Q8
15.00
4.25
4.25

Q9
11.3
4.27
3.65

Q10
15.00
5.38
5.54

Q11
17.25
2.91
11.2 – 8.1

Q12
17.29
11.1 – 8.1
10.2 – 7.8

Q13
14.4 – 10.7
4.3 – 2.3
3.7 – 1.8

These look a lot different to the readings I took yesterday.

Thanks again.

[1878]

I've admitted defeat. I'll salvage the LDR's for another build, but I think this one's had it. I've checked all the resistors, caps & they're all correct values/orientation etc. I've reflowed all solder joints more than once & swapped out a couple of parts that I thought maybe dodgy. The audio probe picks up a loss of volume at Q1 which is carried on throughout the build. There's also a drop in voltage after r7 (1.2m) which feeds Q1 & Q2. This seems to be the norm though.

Never mind.