AD 3208 Wiring Question

[fretbuzz2003]

I am in the process of building the AD3208 from the GGG website and I am a little confused with the stomp switch wiring shown on the parts layout. It doesn't appear to be wired in the normal input jack, effect input, bypass, effect output, output jack fashion. It appears that three of the switch's lugs are wired to different parts of the circuit.

Can anyone who has built this box shed any light on the wiring? To complicate things I am using a 3PDT switch.

Thanks,
Kurt

[Jason M.]

The bypass wiring for the AD-3208 uses a millenium bypass to allow true bypass and LED indicator with only a DPDT switch. The wiring may look strange if you haven't used a millenium bypass before. Read RG's Technology of the Bypass article at geofex.com

You can trace the input and output jack to the switch by looking at the layout diagram and following the appropriate wires. The effect output is taken from the pad second from the right end of the PCB (looking at it with the row of pads on top). The effect input is located at the pad third from the right end. A wire from the switch is connected to the gate of the JFET to turn the LED on and off.

You can use a 3PDT switch, just leave the last column of contacts unused.
Looking at the switch from the bottom with the lugs horizontal:

1    4    7
2    5    8
3    6    9

Don't hook anything to lugs 7, 8 and 9. Use lugs 1-6 as in the layout diagram.

When I first wired mine up, the LED stayed on whether the effect was switched in or out and it popped when switched. After tracing the layout, I noticed that the diode between the gate and drain was backwards. The diode is located directly above the 1M trimpot. The band on the diode should be pointing to the RIGHT not the LEFT. The LED now turns on and off.

I hope that clears up some things.

[fretbuzz2003]

Thanks Jason, that is a big help. I wired it up as you suggested, however when I plug it in no sound goes through nor does the LED light up.

I'm wondering if I have the power jack hooked up correctly. I'm using the plastic DC jack from Small Bear. I have the positive wire hooked up to the shell and the negative wire hooked up to the center jack. I'm not using a battery so I left the other lug alone. Does that sound correct?

Thanks.

[Jason M.]

The power jack sounds like it is wired correct. Are you getting power to the ICs?

Check the voltages on the circuit to make sure power is in fact getting to the right places. The points labelled P on the schematic should have around +9 volts, points S should have +8.2V, and R should have +4.5 volts. You may want to do this without the chips installed in case there is a problem. Go ahead and check the ground points too.

If you are getting power, make sure the ICs are in the right way.

You also said that no sound goes through. Does that mean that you don't even get bypassed signal? If so, double check the wiring on the jacks and switch.

As far as the LED, is the cathode (usually the flat end) connected to ground?

The DIY FAQ, GEO FAQ, and the Debugging page can be tremendous help.

[fretbuzz2003]

Jason,
Thanks for your help. I got the pedal working today. Turns out I forgot to solder one of the leads to a resistor. Duh. Anyway, the pedal sounds fantastic.

I switched the diode you said was pointing the wrong way. Does your LED turn off or just dim? Mine just dims when it is bypassed. Maybe if I increase the 4.7k resistor before the LED it will help?

One other question. I've never owned an analog delay before. When I have the level all the way up and the delay time turned down, the pedal oscillates out of control. Is this normal?

Thanks,
Kurt

[Jason M.]

Jason,
Thanks for your help. I got the pedal working today. Turns out I forgot to solder one of the leads to a resistor. Duh. Anyway, the pedal sounds fantastic.

Great! Glad to hear that.

I switched the diode you said was pointing the wrong way. Does your LED turn off or just dim? Mine just dims when it is bypassed. Maybe if I increase the 4.7k resistor before the LED it will help?

My LED turns off completely. Check that the 22k resistor in the upper left part of the board is connected from the JFET source to ground. That resistor should bleed off any current when bypassed and completely turn off the LED.
Did you use a super bright LED? I'm not sure if that makes any difference...this is the first project that I've done with a millenium bypass...usually, I just use a 3PDT. Search the forum for posts about the millenium...I seem to remember reading about people having the same problem.

One other question. I've never owned an analog delay before. When I have the level all the way up and the delay time turned down, the pedal oscillates out of control. Is this normal?

That is quite normal and one of the beauties of an analog delay. Turn the repeats all the way up and tweak the delay time when it starts to oscillate for some fun noise.

Did you have to tweak the trimpots much when setting it up? I found that when checking it out on the oscilloscope, my initial settings that I did by ear were pretty much spot on. So, I think just going through and setting for the least distortion works fine.

[fretbuzz2003]

I did use a superbright LED. I'll check out the posts like you suggest. I've always used the 3PDT switch as well. They are easier to build and just as cheap (at least when Aron sells them for $6, thanks Aron!)

Thanks again for all your help Jason. This was my 4th successful pedal. I think it's time to tackle the Neovibe!   :twisted:

[Jason M.]

No problem for the help.

You can help me with the Neovibe when I need it!