Build Your Own Clone Message Board

Hello,

This is my first build, so I apologize for any stupid questions/assumptions right off the bat:

After having put my Classic Overdrive kit together, I connected a battery and plugged it inline into my amp. In bypass mode, my guitar signal passed through it normally into my amp. However, upon engaging it, I received no signal from the guitar - what I DID get coming through my amp was the radio signal that I tend to get in all my audio gear, which I'm fairly certain is being broadcast from the top of the Prudential Building (I'm in Boston's Back Bay area, very close to the building). Strangely, the signal was LOUDER when the Drive knob was further counter-clockwise, and SOFTER when I moved the knob clockwise. The LED lit fine when the effect was engaged.

I removed the connections to the footswitch and in/out jacks, and resoldered them, as I thought that I had probably screwed something up during this process. This assumption was based on the fact that before even ordering a pedal, I bough several small electronics project kits from Radio Shack to practice my soldering, and after a few of them, my joints seemed to look pretty solid, so I didn't think it was a problem with the components on the PCB.

I was taking pictures of the PCB and was going to flip it over to show the underside when I came up against the following problem: wouldn't I have to sever the connection to the power jack in order to remove the PCB and flip it over, because this jack is inserted from the outside of the pedal and then connected via leads inside? If this is indeed the case, and it is necessary for me to desolder the switch in order to take the pictures, I'll certainly do it, but I wanted to ask in case I was making a dumb mistake and didn't realize something obvious.

Thank you in advance to anyone who can offer me any pointers - I'm really psyched about this project and definitely want to get it working!

P.S. I'm obviously having trouble resizing this pictures - I tried resizing them to roughly 500x500 pixels like it said it the tutorial, but they keep coming out tiny when I post the code in the forum (forgive my forum/coding/online illiteracy - can anybody help?!

I fixed the display coding in your post--you had used the URL for a thumbnail photo, which was the ".th" in the coding.

Your opamp is installed upside down. Hopefully it's not damaged, so just remove it from the socket (be careful not to damage the legs) and install it with the dot in the upper left corner when viewed with the footswitch at the bottom.

Thanks so much for the quick reply and the help with the pictures - I very much appreciate it! I had been looking at the large image of the PCB that came with the instructions and suddenly noticed that mine looked upside down, so I flipped it over and tried the pedal (this was a week or two ago), and I got the same problem, but louder. So I thought that maybe I was correct in the first place, but I guess I was right in changing it so thank you for confirming that for me! I'll flip it again, carefully, but I guess I'm still in the same boat as far as the radio interference.

Disconnect everything but the DC adapter. You should be able to pull the "guts" up out of the pedal with those 3 wires still attached and acting like a hinge. Pivot the board up out of the enclosure and you should be able to get a couple of photos of the back of the PCB. I'd also like to see a bigger photo of the front of the board, to be able to make out all of the resistor color coding.

Good point regarding the jack - please let me know if these work:

I don't see anything obviously amiss. Do you have a multimeter available to do some continuity and voltage measurements?

It's funny - I work in a hardware store, so I can get a DDM at quite a discount, and yet I still haven't purchased one yet. I suppose tomorrow during my shift would be a good time to do that...

Thanks for all your help and quick responses, by the way!

I just finished my first build yesterday. I was getting my guitar to bypass through the pedal no problem. When I clicked the pedal it wasn't passing through but I was getting distorted fuzz (no guitar though). The funny thing was that the volume on the pedal was working! I lifted the board a little and figured out my volume pot was touching the soldered side of the board so I bent it out a little and for extra measure put some electrical tape in between. Maybe that is it? I also had one of my solder points from the output touch inning one of the pots so I had to correct that.

Signal path shots to ground are always something to look out for. Keeping the component lead ends and wire ends trimmed down as close to the top of their solder joints as possible is important to avoiding such shorts, particularly against the backs of control pots which are grounded through the pedal enclosure.

Those are good points regarding shorts - thanks for pointing that out! I just bought that DDM today, so tomorrow when I can go buy some batteries for it I'll fire it up and try to diagnose. I'm not sure what voltages I should be looking for/continuity between which lugs, etc, but I feel like I've seen something posted around here with specific things to look for. Would you mind pointing me in the right direction as far as troubleshooting with the DDM? Thanks very much!

Let's start by checking the circuit integrity going into and coming out of the PCB. With the footswitch engaged, check for continuity between the following pairs of points (refer to the labeled PCB diagram below for the referenced resistor locations):

1. The tip of the input jack and the top of resistor R1
2. The tip of the output jack and the top of resistor R16

The first one checks for signal path continuity from the input jack through the footswitch and into the start of the effect circuit. The second checks for continuity between the end of the effect circuit, through the footswitch, to the output jack. It is not necessary to have power hooked up to the circuit or for cables to be plugged into either I/O jack for this continuity testing. In fact, it's better if they're not.

I checked both these connections with the DMM, and there does seem to be continuity in both, though sometimes I need to finagle the leads on the tops of the resistors a little bit before I'll get a constant beeping from the meter.

Would you mind suggesting a few more continuities/voltages to check for?

OK, let's check the voltages on all of the pins of the opamp. The #1 pin is the one at upper left, adjacent to the dot marker. The pins are numbered down the left side and back up the right, so that the #8 pin is across from the #1:

1----8
2----7
3----6
4----5

You'll need to have the pedal powered and a cable in the input jack to take these DC voltage readings. Touch the black probe of your meter to ground and use the red probe to test each pin. Report the results here.

Is ground the chassis in this case? Kindly forgive my lack of electrical knowledge...

If I did this correctly, the voltages I read were as follows:

4.09V 8.26V
4.07V 4.07
4.09V 4.07V
0V 4.11V

So the anomaly is that there doesn't seem to be any voltage across pin 4 - could this be the source of the problem? Or did I take the readings incorrectly anyway, as I touched the black probe to the case while I took them?

Thanks for your help!

Yes, the chassis is ground.

There is no voltage at pin 4 of the op-amp because that is it's ground connection.

Your voltage on pin 8 seems low. What are you using to power the circuit?

I was using a Duracell 9V battery - though I do have a 1-Spot on my pedal board that I could conceivably hook up to it, if you think that would be a better way to go?

That's what I would do. That 8.26V is on the low side for a battery.

So I hooked up the pedal to my 1-Spot and got the following:

4.71V 9.47V
4.69V 4.70V
4.71V 4.70V
0V 4.72V

This is more or less the same as what I got with the battery, just proportionately higher, I suppose. In this indicative of any particular trouble?

No, those values are all right on the money.

At this point, I'd suggest tracing the signal path with a signal tester. This will allow you to pin down where the signal is dropping out. Most likely, you have a bad solder joint in there somewhere--this is far, far more common than a bad component.

Did you not say you have this problem with all your audio gear? Did you try it in another location? Maybe a different room or even outside our house?

I do have a radio interference problem with all my other gear, but the thing is, all my other gear works, i.e. I can still pass audio through it, and only hear the radio very faintly if there's nothing playing.

With the pedal, there's no guitar signal at all when it's engaged (fine when bypassed), and then there's the faint radio signal, also. So I don't think that trying it someplace else would do it.

In other words, instead of being both a pedal AND a radio, your Classic Overdrive is just a radio!

Try the signal tester route next. Here’s a good sequence to work through for tracing the signal through the Classic Overdrive circuit. With the effect powered, your guitar plugged into the input jack, and the footswitch engaged, use the signal probe to test the following points in the circuit (see reference diagram below), in the order shown. When the signal “drops out”, you will have localized the problem between that portion of the circuit and the previous good test point:

1. Tip of input jack
2. Lug 4 of footswitch
3. Lug 5 of footswitch
4. Top leg R1 resistor
5. Q1 base (middle leg)
6. Q1 emitter (top leg)
7. Opamp pin 3
8. Opamp pin 1
9. Opamp pin 5
10. Opamp pin 7
11. Volume pot lug 3 (left)
12. Volume pot lug 2 (middle)
13. Q2 base (middle leg)
14. Q2 emitter (bottom leg)
15. Top leg R16 resistor
16. Lug 7 of footswitch
17. Lug 8 of footswitch
18. Tip of output jack

Excellent - thanks for posting that! Now I just have to order a signal tester...I guess I'll post back once I've received it and done the test