ilovefuzz.com

Good afternoon!

I just recently printed my first board, an MXR Distortion +.

I have run into an issue after populating and wiring the board where if the pin on the LM741 op amp that is not supposed to be attached is, I get an interesting oscillation that changes in pitch as I turn the volume potentiometer-- and behind this horrible noise is the distortion effect I WANT to have sans oscillation. If the pin is detached, I only have a clean signal passing though the board that can be turned up and down with the volume knob.

Any ideas out there would be great! This is my first post here, so if you need some more information to assist me I can supply that.


Thanks in advance!

EDIT: The gain is jumpered right now instead of having the pot in there-- it makes the same sound if I have it attached.

Pictures help. It always helps to see what exactly you have, not just your schematics and layout. Good high res pics of both sides where we can examine the traces and see the part values and orientation as well as how you have your jacks and power connections, switching etc wired up. It could be something obvious or not so obvious. There are 3 pins not used on the LM741, so when you say the one not used, that doesn't help. There is nothing connected to pins 1, 5, or 8.

Thanks for the reply, I can supply those. I apologize for the lack of specificity-- the pin that, while connected, makes the oscillation + distortion happen is pin 4. That pcb layout appears to have that pin knocked out, but when it is...a clean signal comes through. The pins you described are isolated on the board to copper traces that are not connected to anywhere else.

I know my soldering looks atrocious, but I misplaced my solder braid and don't have a pump currently...learning as I go!

Images: http://imageshack.us/a/img189/3523/sx90.jpg
http://imageshack.us/a/img18/3705/cq5j.jpg (the gain jumper is not in this image, but it is there when I am testing. also, pin 4 is not in contact
with its neighbor.)

And the jacks and pots:

http://img19.imageshack.us/img19/7374/d0x4.jpg

Big pictures are big! They're all in this tag:

Well you have a wire going from the input jack (tip) to the output jack (tip) that shouldn't be there. The pin you cut off is the - (ground in this case) you kinda need that. Looks like a few cold solder joints maybe too. I'd say replace the op amp, but it doesn't look like there's much pad left under pin 6 which is the output.

AHHH!!! The wire did the trick! Thank you so much. I am very proud of my first build now

cool, glad that's all it was. Have fun with it!