This is a library of perfboard and single-sided PCB effect layouts for guitar and bass. I'm not an electrical engineer by any stretch of the imagination, just a DIY'er who likes drawing layouts. It is meant for the hobbyist (so commercial use of any of these layout is not allowed without permission) and as a way to give back to the online DIY community.

Thursday, November 6, 2014

MXR Distortion +

The classic '70s overdrive by MXR, and is essentially the same as the DOD 250 and Ross Distortion. I designed the layout to have onboard pots, to alleviate some offboard wiring. It also has the LED resistor on the board, again to reduce offboard wiring a bit.

It'll fit perfectly in a 1590B enclosure. Might be a good idea to socket the diodes. The original had germanium diodes, but silicon diodes or LEDs will sound good as well (just different). 


39 comments:

  1. the 10pf cup has no through holes in the layout, i just placed it with the 1m resistor next to it, did the rest just like in the layout, BUT its not working ! :/ too bad! i hatched it and everything, maybe theres a mistake in the layout somewhere (its not my first pedal, so its not an idiot soldering mistake from my part)

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    1. Fixed and updated the PCB image. Went over the layout again against the schematic and it should work. Wonder if you've got a bad component or a copper bridge somewhere. You go over everything with a multimeter?

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    2. ill try to replace all the components, yes i went all over it with the multimeter, and checked for bridges, its killing me i dont understand y its not working for me, i got no signal going out, and when im shorting the circuit with my finger at some places i do get some wet signal... any idea??

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    3. Before you replace all the components, have you tried using an audio probe to find where the fault is? Here's a link to the method I've used to debug troublesome boards.

      http://www.diystompboxes.com/pedals/debug.html

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    4. thanks man, ill definitely try audio probe, BTW, i don't have a rev log pot so i'm using a regular one, that couldn't be the reason its not working right?

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    5. Yeah, that won't keep the effect from working. The rev log pot just allows better control of the distortion.

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    6. well, i did the audio probe, the input (leg 3)of the opamp receives signal, but nothing on the output (leg 6) on all the op amps i have what can it be ? (there is nothing no where else on all the board except from the input until leg 3 of the opamp)

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    7. Are you using a 741 opamp or something else?

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    8. iv'e tried a ua741 and tl071, more then one from both

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    9. what dose the new Diod4001 from 9v to 1uf Tant do ?

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    10. The 1N4001 is just for polarity protection.

      I'm not sure what else to tell you. I had the random thought that if you're using a socket for the IC it might have a short or broken connection in it, but that seems unlikely. Post some pics of the board if you can.

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    11. holly fu*** sh** http://diyaudioprojects.com/Forum/viewtopic.php?f=10&t=5015
      my single opamp with UA741CN written on it is actually a dual opamp!! so so sorry for all the trouble, the MXR works fine! i connected one opamp from the dual and it works, and even sounds very nice! :) thanks a lot!

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    12. Glad you got it sorted out. Didn't know they made dual 741s. Good to know. Thanks for the verify!

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    13. they dont really make a dual 741, they're just marking 741 on a dual opamp, (some sort of a lame counterfeit) and thank you !

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    14. they dont really make a dual 741, they're just marking 741 on a dual opamp, (some sort of a lame counterfeit) and thank you !

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  2. for original part https://www.youtube.com/watch?v=g59a7S7B128

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  3. for mod part https://www.youtube.com/watch?v=75TVqVDlCt8

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  4. Are tantalum capacitors polarized?

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    1. In this layout do not show the polarity.

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    2. The negative leg of both tantalums faces the potentiometer side of the board.

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  5. If someone could help me, please... I can't see the location of the 4001 diode...

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    1. Huh. Apparently I forgot to copy that diode over from the perf layout to the PCB. You can leave it out as it's just the polarity protection diode. Or you can add it off board going from +9v to ground (cathode to +9v).

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    2. thanks!! I´m gonna do the second way, thanks again!! :D

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  6. Is that a typo on the green caps should they be nf not uf

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    1. Oh wow. Yeah old typo. Haha Definitely nF

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  8. Any good replacement for rev log pots? Can´t find it anywhere in
    my country. Thanks!

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    1. Try using a linear 1M pot instead.

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    2. Thanks!!! Love you blog! You are the man! Keep the awesome work!
      By the way is there any recipe for rev log pots replacement like "change it for a double resistance linear pot"? As you suggest in this case? Thanks again!

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    3. That doesn't always work... Really depends on the circuit. You can just use a similar value in a linear taper, but there's really not much of a work-around for a rev log pot other than experimenting.

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  9. Hum, I´m having a problem when I activate the effect. The pedal doesn´t sound right after being stomped. What could that be?? I replaced everything but the 10pF cap. Does it something to do with my issue?

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    1. Time to learn how to debug!

      http://www.diystompboxes.com/pedals/debug.html

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    2. Well, I checked everything before making the audio probe. With the audio probe I noticed that everything in the circuit was ok. I was so desperated because I couldn´t find the answer even with the probe, when I realized that Ididn't check the switching part of the pedal. For some reason I can´t remember, I didn't make the right connections, I was using a diagram I found somewhere else on the net. And for some weird reason I noticed that, when switched on, the signal was pasing through the circuit signal and the bypass signal. I´m trying to figure this out yet, but I can´t really say exactly (yet, I hope to revise the old connection and come to a conclusion) wha was going on. Thanks for the advice, it helped me to think about the effect as a whole and not only focusing in th circuit part of it. :D

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  10. Please help! Have made two of them now. #1 has no distortion and distortion pot does nothing. #2 has full distortion and distortion pot does nothing. Have tried a500k pot for distortion on both pedals. Makes no difference.

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    1. You should be using a C500k (reverse log)

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    2. That's what I tried at first. Tried a500k just to see what happened and no difference. Weird how they both do it. Could be from my leaving out the 4001 since it wasn't on the pcb or something? The distortion pots don't do anything.

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