Second Pedal Build - Engineer's Thumb - Help needed

[Jordash]

Hey guys,

After the success with my first pedal I've had a crack at another.

This time I've gone for the Engineer's Thumb. I have built this to lvlark's schematic:
http://tagboardeffects.blogspot.co.uk/2012/11/engineers-thumb.html
Using LM13700 Daughterboard:

http://2.bp.blogspot.com/-P7jqffl_ejk/UHVUB0pXl-I/AAAAAAAAC-k/p2HwRW-52S0/s1600/LM13700+Daughterboard.png

I have done the LM13700 Version.

The build went well and I get a bypassed sound fine, but when I turn it on I don't think it's working.

With the volume all the way up and the ratio all the way down it sounds like normal bypassed signal, volume the same. The volume knob works as expected when turned down.

The ratio pot does not work. The first 5-10 degrees of clockwise travel yield no real change, although there is some additional noise, further turning of the pot just makes it crackle and for the remainder of the pot turn there is no output.

The only part substitutions I've made is to use 1N4008 Diodes (i think), as that's what I had.

Now for some voltages (all with ground lead attached to outer of jack plugged into input). Also voltages taken with the bright switch closed.
+ive - 8.98V (wall wart)

Q1
C = 4.49
B = 2.88
E = 3.52

IC1 (LM13700), figures in bracket equivalent to circuit with CA 3080 pin number.
1.   = 1.47 (Pin 5)
2.   = 0.00
3.   = 4.49 (Pin 3)
4.   = 4.49 (Pin 2)
5.   = 4.49 (Pin 6)
6.   = 0.00 (Pin 4)
7.   = 0.00
8.   = 0.91
9.   = 0.40
10. = 0.00
11. = 8.98 (Pin 7)
12. = 0.003-0.005
13. = 0.00
14. = 0.00
15. = 0.00
16. = 0.00

IC2 (TL072CN)
1. = 2.48
2. = 3.18
3. = 3.17
4. = 0.00
5. = 4.28
6. = 4.49
7. = 4.49
8. = 8.98

IC3 (TL072CN)
1. = 4.50
2. = 4.49
3. = 4.08
4. = 0.00
5. = 4.08
6. = 4.49
7. = 4.81
8. = 8.98

I have been through the circuit and checked for solder bridges, etc. I have continuity checked between each row, no obvious problems there. I also checked the resistance of all the resistors, most were fine. Obviously with the circuit built the resistance is affected by the rest of the circuit, those resistors that showed different I then check the colour code of, again, no obvious issues.

I will follow this post with some photo's of the circuit out of the case, but that's easier to do directly from my phone.

Thanks in advance for the help.

[Jordash]

Photos :

[Jordash]

Is anyone able to shed some light on this?

[merlinb]

Q1
C = 4.49
B = 2.88
E = 3.52

Are you sure about this? The emitter should be at 4.5V, and collector at a lower voltage.


IC1 (LM13700), figures in bracket equivalent to circuit with CA 3080 pin number.
1.   = 1.47 (Pin 5)  <- this is connected to the collector of Q1, how can it be at a different voltage?
2.   = 0.00
3.   = 4.49 (Pin 3)
4.   = 4.49 (Pin 2)
5.   = 4.49 (Pin 6)
6.   = 0.00 (Pin 4)
7.   = 0.00
8.   = 0.91
9.   = 0.40
10. = 0.00
11. = 8.98 (Pin 7)

IC2 (TL072CN)
1. = 2.48 <- This is connected to the base of Q1. How can it be at a different voltage?
2. = 3.18
3. = 3.17
4. = 0.00
5. = 4.28
6. = 4.49
7. = 4.49
8. = 8.98

[Jordash]

Thanks so much for the comments, ill have to look at it again. Probably shows where I've messed it up! Cheers.

[Jordash]

I've rechecked my voltages and they're much better than those posted previously. I think I did a duff job of measuring them! I'll try and post them up later. They look ok, bit I'm no expert.

I'm still finding that the ratio pot doesn't seem to work very well. I've put a meter across it and the resistance change is smooth.

[pinkjimiphoton]

i would check the rail side of your vero, it looks to me like a few potential solder bridges might be there.
run something between the tracks and make sure there's no short.
i'm betting it's a bridged track somewhere.

[Jordash]

Thanks for the advice. I'll check it again, I've run a stanley knife between the tracks quite a few times and I've also used a continuity checker between rails, but there's definitely no harm doing it again!

Updated voltages, now that I'm being a bit more careful about how I read them:

V+ - 8.98

Q1
C - 1.46
B - 3.84
E - 4.14

IC1
1 - 1.47
2 - 0
3 - 4.49
4 - 4.49
5 - 4.49
6 - 0
7 - 0.21
8 - 0.21
9 - 0.12
10 - 0
11 - 8.98
12 - 0
13 - 0
14 - 0
15 - 0
16 - 0

IC2
1 - 3.64
2 - 4.28
3 - 3.9
4 - 0
5 - 4.28
6 - 4.49
7 - 4.49
8 - 8.98

IC3
1 - 7.73
2 - 3.05
3 - 4.08
4 - 0
5 - 4.08
6 - 4.49
7 - 4.81
8 - 8.98

Being the beginner that I am I unfortunately need advice on how to interpret these values. From what I understand the voltages on Q1 are in the right sort of region.

[midwayfair]

1. Did you jumper pins 1&5 of IC2?
2. I can't see it too well, but it looks like you didn't use a 220R right next to the PNP transistor.
3. Your 4.7nF adn 100nF caps -- are those caps the right values? They look physically too small to be the right part values.
4. When you play your guitar, do you get a change in voltage on the control pin at all?