neovibe troubleshooting - not working correctly

[larsthestrat]

Neovibe, from General Guitar Gadgets

I followed the lay-out (http://www.generalguitargadgets.com/projects/20-modulationecho/121-neovibe), no mods done yet. I used 2N5088 for all the transistors, and one 2N3904 for the lamp driver. I used a Hahn 18v power transformer. I do have a clean signal when the pedal is off, but with oscillation. When the pedal is on I don't have a really good signal, but a very distorted sound (not loud). I do have a very heavy oscillation when the pedal is on. The lamp is going on and off but only when the speed control, TR1 and depth control are fully open and the light is not very fierce. When I dial the speed knob/TR1/Depth on 75% the lamp is off. I live in Europe so different currents here from wall power. I checked for all the components and soldering that seems to be fine so far. I hope someone can help me out. Here are some results for the measurements on voltages.
Q1
C =1,7
B =0,7
E =0,7

Q2
C=3
B=1,7
E=1,24

Q3
C =8,8
B =3
E =2,8

Q4
C=11,7
B=3,3
E=3,7

Q5
C =8,7
B =3,7
E =2,8

Q6
C=11,8
B=3,3
E=3,6

Q7
C =8,7
B =3,8
E =2,8

Q8
C=11,8
B=3,3
E=3,6

Q9
C =8,7
B =2,6
E =2,8

Q10
C=12
B=4,3
E=4,7

Q11
C =13
B =2,4
E =6,7

Q12
C =13
B = 7
E =6,8

Q13
C =11,4
B =1,2
E =0,7

D1=
A = 6,7
B = 6,7

D2=
A = 6,7
K = 6,7

DB1 = 15V

7815
I = 13
G = 0
O = 11,2

[R.G.]

C =1,7
B =0,7
E =0,7

If this measurement is correct, then this is one place that the distortion could be coming from.

Measure again, with red lead on base and black lead on emitter, and post back here.

Q11
C =13
B =2,4
E =6,7

same recommendation; remeasure with red lead on base and black lead on emitter.

7815
I = 13
G = 0
O = 11,2

The regulator is starved for voltage. It needs at least 17V dc on the input.

[larsthestrat]

Thanks. I will post the results of the measurement for both transistors this weekend.

This is the tranformer they send me:
http://www.banzaimusic.com/Hahn-BV2020159.html

it says 12v but when I connect it to the wallpower, it gives 18VAC output, after DB1 I have 15VDC.

i have another one which supplies 2 x 12V, use that one?

[lietuvis]

DB1 = 15V

7815
I = 13
G = 0
O = 11,2

If you have 18V out of transformer but only 13V after bridge rectifier is something not good there. the 7815 needs around 17V to work ok to give you a 15V on output under load. if there is only 11.2V on output, the regulator is not working correctly, it might due to your trnsformeris not coping due overload of circuit as it is only for 42mA @ 12V. try other more powerful transformer at least 200mA @ 12-15VAC and see if you get 15VDC on 7815 out that might resolve your hum(oscilations). Thats my opinion for starting point to debug circuit.

[lonewolf]

I built a neovibe and had a very similar problem..I replaced q1,2,3 and the noise went away..I also had low voltages on q1 which was solved also..every thing else was mpsa42's....using sockets really paid off...

[larsthestrat]

oke, both Q1 and Q11 give 0,4V from base to emitter. Is this correct?

I will change the transformer. I have also this bigger one:
http://www.banzaimusic.com/Hahn-BVEI3821190.html

[larsthestrat]

oke, I have the bigger Hahn connected (24V) and the lamp is much brighter, the regulator has the correct voltages now. But still this squeeling sound and almost no signal when engaged.
Shall I post new measurements?

[larsthestrat]

Here are the new results for the measurements on voltages after using the the bigger PT. I also checked the voltage between emitter and base (E-B). Hope you'll find the time to respond.
Q1
C =2
B =0,9
E =0,8
E-B=0,4

Q2
C=3
B=2
E=1,5
E-B=0,5

Q3
C =10
B =3,7
E =3,7
E-B=0

Q4
C=14,9
B=4,6
E=4,3
E-B=0,3

Q5
C =11
B =4,2
E =3,7
E-B=0,6

Q6
C=14,9
B=4
E=4,4
E-B=0,3

Q7
C =11
B =4,4
E =3,8
E-B=0,6

Q8
C=15
B=4,1
E=4,3
E-B=0,3

Q9
C =11,5
B =4,3
E =3,7
E-B=0,6

Q10
C=15
B=5,2
E=6,2
E-B=0,23

Q11
C =30
B =6
E =16
E-B=0,45

Q12
C =30
B = 16
E =12,5
E-B=0,55

Q13
C =25
B =2,5
E =2
E-B=0,6

D1=
A = 15
B = 15

D2=
A = 15
K = 15

DB1 = 30V
7815
I = 30
G = 0
O = 15

[R.G.]

Q3
C =10
B =3,7
E =3,7
E-B=0

If this measurement is correct, this is a big problem. This transistor cannot be passing audio properly if its base and emitter are both at the same voltage. There may be a short on the PCB between these two points.

Q10
C=15
B=5,2
E=6,2
E-B=0,23

Odd. Perhaps OK, perhaps not. Work on Q3 first.

[larsthestrat]

oke, I cleaned the PCB (no visible traces of solder), nog change in voltage. Swapped a new transistor in, now I have 3,8 (emitter) versus 3,91 (base) en 10,5 (C).
Is this better?

[R.G.]

Better. Not the same is better.

What does it do now?

[larsthestrat]

squeeling like hell......lot's of oscillation. Should I post some pics? Somebody mentioned lowering the input voltage bij adding a resistor between C24/C25 (getting it down to 24V instead of 30V now).
Checked the components once more, they seem to be fine.

[R.G.]

Squealing on a univibe circuit is usually either a problem with the wires to the controls or the compensation capacitor on the base of Q3 being missing, not connected or incorrect value.

[larsthestrat]

here are some pics, hope you'll find the time to review them.

[larsthestrat]

anybody, I'd like to know wheter I made a mistake in the wiring.....

[larsthestrat]

Anyone, please???

[lietuvis]

Anyone, please???

get the solder side of board as well. looks ok from top.

[larsthestrat]

some new pics from the back. A few things I did:
- soldered a 330 ohm resistor between C25 and C25 (and cut the trace) to lower the voltage from the PT
- I now have 20,4V/0V/14,9V on the regulator, so that seems better now
- I put the PCB in a metal housing and the squeeling became more low, but still loud
- To trace down the squeeling noice I removed C17, the squeeling was gone, so I guess the first part of the soldering is okay
and it should be in the LDR part (isn't it?)

Here the pics of the back of the PCB, hope they're sharp enough:

[larsthestrat]

any remarks about the last post?

[R.G.]

Next step is an oscilloscope, or if you don't have one, an audio probe. Trace the signal through the signal path, checking for where it starts.