AD3208 debugging

[carrejans]

Hi guys, I made an AD3208 delay circuit from GeneralGuitarGadgets. It wont work. Can you help me figure out what the problem is? Thank you.


Schematic: http://www.generalguitargadgets.com/diagrams/ad3208_schematic.pdf

Layout: http://www.generalguitargadgets.com/diagrams/ad3208_lo.gif

Part substitutions:
-   2N5457 iso 2N5485
-   NE570N iso SA571
-   V3102D (Coolaudio) iso MN3102
-   V3205D (Coolaudio) iso MN3208 or BL3208
-   A regular 1W 8V1 zener iso suggested 1N4738

I use a battery with voltage 8.55V
I set all trimmers at half.

When I switch the effect on:
-   The guitar sound comes unmodified out of circuit. No delay at all.
-   When I switch on, the led lights up for a fraction of a second.

Some measurements:

NE570N:
P1: 7.36
P2: 7.31
P3: 7.31
P4: 8.56
P5: 7.67
P6: 7.53
P7: 7.29
P8: 0
P9: 7.72
P10: 7.68
P11: 7.68
P12: 7.82
P13: 7.91
P14: 7.29
P15: 7.29
P16: 7.33

V3205D (left one on the layout):
P1: 0
P2: 4.30
P3: 3.61
P4: 3.65
P5: 8.07
P6: 4.29
P7: 3.15
P8: 7.48

V3205D (right one on the layout):
P1: 0
P2: 4.29
P3: 3.88
P4: 3.92
P5: 8.06
P6: 4.29
P7: 3.69
P8: 7.48

TL072CN:
P1: 7.96
P2: 7.93
P3: 7.32
P4: 7.81
P5: 7.32
P6: 7.87
P7: 7.95
P8: 8.52

V3102D:
P1: 8.06
P2: 4.29
P3: 0.57
P4: 4.29
P5: 4.28
P6: 4.35
P7: 4.13
P8: 8.06

2N5457:
G: 0.16
S: 0.16
D: 0

2N5088 (left one on layout):
E: 0
B: 0
C: 8.50

2N5088 (middle one on layout):
E: 7.02
B: 7.00
C: 8.50

2N5088 (right one on layout):
E: 0
B: 0
C: 8.50

ZENER:
A: 0
K: 8.06

1N4002:
A: 0
K: 8.49

1N4148 (upper one on layout):
A: 0.16
K: 0.05

1N4148 (middle one on layout):
A: 0
K: 0.16

1N4148 (bottom one on layout):
A: 0.57
K: 0



The first thing I notice is the values of the transistors that aren't looking good.
Also the datasheet of the NE570 states that pin4 should be ground.

[GP]

Pin 4 of your opamp should be ground too... the difference between pin 8 and pin 4 on the opamp is suspiciously close to a diode drop

are you sure you have your 1N4002 the right way round? should be the "wrong" way round, if you see what i mean.

[Jason M.]

Hi,
I built this pedal a couple of years ago, but don't have it near me to check voltages. I'll do that when I get home later, but a few things look curious.
Transistors: emitter voltages look high.
Op amps: voltages on all pins are close to each other. You should have at least one at ground and some at bias supply voltage.

Start by checking your grounds and make sure the IC pins that should be connected to ground are actually grounded.
Check your bias supply.

I'll post my voltages later.
Good luck.

[carrejans]

Thanks guys. Will look at it later today.

[carrejans]

I found two errors in the mean time. 
One of the diodes was placed wrong.
And the etch of the ground trace was interrupted at one place.
Fixed those two problems. But still not working. I just get an unmodified sound at the output.
Here are my new measurements:

BATTERY:
8.39

NE570N:
P1: 0
P2: 1.79
P3: 1.79
P4: 0
P5: 1.81
P6: 4.59
P7: 4.59
P8: 1.81
P9: 1.81
P10: 4.56
P11: 1.77
P12: 1.81
P13: 8.35
P14: 1.80
P15: 1.80
P16: 1.40

V3205D (left one on the layout): (ALMOST UNCHANGED)
P1: 0
P2: 4.30
P3: 3.61
P4: 3.65
P5: 8.07
P6: 4.29
P7: 3.02
P8: 7.48

V3205D (right one on the layout): (ALMOST UNCHANGED)
P1: 0
P2: 4.29
P3: 3.88
P4: 3.92
P5: 8.06
P6: 4.29
P7: 3.69
P8: 7.48

TL072CN:
P1: 4.19
P2: 4.19
P3: 4.18
P4: 0
P5: 2.08
P6: 4.18
P7: 4.18
P8: 8.33

V3102D: (ALMOST UNCHANGED)
P1: 8.06
P2: 4.29
P3: 0.57
P4: 4.29
P5: 4.28
P6: 4.35
P7: 4.13
P8: 7.47

2N5457:
G: 0
S: 0
D: 0

2N5088 (left one on layout):
E: 0
B: 0
C: 8.32

2N5088 (middle one on layout):
E: 3.92
B: 4.40
C: 8.32

2N5088 (right one on layout):
E: 0
B: 0
C: 8.32

ZENER: (UNCHANGED)
A: 0
K: 8.06

1N4002: (ALMOST UNCHANGED)
A: 0
K: 8.30

1N4148 (upper one on layout):
A: 0
K: 0

1N4148 (middle one on layout): (THIS IS THE ONE THAT I HAD TO REVERSE THE POLARITY OF)
A: 0
K: 0

1N4148 (bottom one on layout): (UNCHANGED)
A: 0.58
K: 0



Hope somenone sees where the problem is.
Thank you very much for all the help!!

[Jason M.]

OK.
Your voltages look much better now but there are still some problems.

Here are the voltages from my pedal.

NE570:
1) 0.95
2) 1.82
3) 1.82
4) 0
5) 1.82
6) 4.59
7) 4.59
8) 1.82
9) 1.82
10) 4.56
11) 1.82
12) 1.82
13) 9.65
14) 1.82
15) 1.82
16) 0.97
Check the caps on pins 1 & 16 on your NE570. The voltages look strange.

MN3205 left:

1) 0
2) 4.41
3) 5.93
4) 5.93
5) 8.27
6) 4.40
7) 4.69
8) 7.76

MN3205 right:

1) 0
2) 4.41
3) 5.40
4) 5.40
5) 8.27
6) 4.40
7) 4.52
8) 7.76
Don't worry about the pin 7 voltage being different from yours. This is the BBD bias, whose setting may vary.

JRC5532

1) 5.0
2) 4.82
3) 4.82
4) 0
5) 4.22
6) 4.64
7) 4.64
8) 9.65

MN3102

1) 8.27
2) 4.40
3) 0.58
4) 4.41
5) 4.49
6) 4.35
7) 4.35
8) 7.76

5088 left:
E) 5.30
B) 5.87
C) 9.66

5088 middle:
E) 3.97
B) 4.53
C) 9.66

5088 right:
E) 4.71
B) 5.28
C) 9.65

Your emitter voltages should be around 0.5V lower than your base.
The two transistors on your pedal that have 0V on emitter and base are not amplifying the signal because they are not biased properly.
This explains why you are getting straight signal but no delay.
Check to make sure that they are absolutely oriented correctly.

Also, check the resistors connected to them.
Look for solder bridges on the transistor pins.

Once you have the transistors biased properly, it is still possible to get straight guitar only, due to the BBD bias setting.
It might be easiest to set the BBD bias trimmer while strumming your guitar and using an audio probe at the output of the first BBD.
Rotate the trimmer until you hear the cleanest signal.
Repeat for the second BBD.

Check to make sure all IC's are inserted the right direction.
It is easy to get spoiled when using R.G.'s layouts because transistors, ICs, caps, diodes, etc. usually all point in one direction.

Are you using electrolytics or film for the 1uF caps?
The electros have to be facing a certain way, but it doesn't matter if you are using film.

Hope this helps.
Let us know how it goes.

J.

[carrejans]

Thank you very much, Jason.
I'm at my parents house right now. I will check your suggestions on Monday, when I'm back.

[carrejans]

Hi guys,

If dug up this projec of mine after a while. Still having the same problem.

Two of the 2N5088's have no correct voltages. Still 0V at base and emitter.
I have changed them with new transistors: no change. I've checked the connected resistors; seems to be fine.

The LED isn't lighting up either. Has to do with the 2N5457 that doesn't work, I assume. (is this the millenium thing?; sorry can't remember the name)

Any idea what the problem is?

Thank you very much.

[sean k]

With something like this it's much easier to look at it as separate blocks and work through it with a set of signal probes. The fet is the least of your problems so don't worry about that yet.

The idea is to get a signal source, guitar if nothing else like an oscillator of some description, with a set of alligator type onnections, or better yet those little connectors we use for the earth on an oscilliscope probe, to create a way to inject signal. Then create another set of probes that go to an amplifier input. With these you can work your way along the signal paths to isolate whats not working properly. Put signal to the ins and attach the amp probes to the outs.

You want to determine that the input opamp is passing signal first then whether the input 571 is passing signal. Then you do the output opamp and the three transistors and finally the output 571. Once all thats been determined to work, or not, and fixed so it does then all you have to do is work on the BBD's and the timer.

It really does help to do it as blocks and isolate areas simply because this effect is big and can have one jumping all over the place when trying to see it as a whole.