Distortion + help, now what did I do....

[6stringer]

Just built a MXR Distortion + using the PCB layout at Tonepad. 
The link: www.tonepad.com/getFile.asp?id=4

There is practically no distortion at all.  There is a lot of noise when the volume control
is dimed.    I used a 100k log pot for the volume,  500k reverse log pot for the distortion.
The 1uf caps are tantalum.    The IC is a 741.   The bypass and LED work correctly.

This is such a straight-forward circuit, I don't know what I've done wrong.
Any ideas?

[Mark Hammer]

Any chance that:

a) the chip is turned around the wrong way?
b) one or more pins on the chip got bent under the chip or are not in contact for some other reason?
c) you've wired up the jack wrong and nothing is going to the chip?

[burnt fingers]

Check your solder joints and wiring meticulously.  I have had a few problem builds in which I believed everything was correct.  I melted a solder joint or two again and bada bing bada bang, bobs your uncle and it works.. 

scott

[6stringer]

I carefully checked the circuit, confirmed the component values, checked the solder joints and confirmed that
the switch wiring is correct according to: www.diystompboxes.com/beginner/circswled.jpg
The IC is mounted correctly, the cap polarities are correct.   I swapped out the IC for another 741 with no change.
I checked all the grounds and confirmed they are good and correct.
The only component that is different is C5, the schematic calls for a 10pf cap and I used a 12pf, do you think that could be it?
Thanks for your help.

[DryRoasted]

When I built my D+ on strip board I had a problem like yours, but it turned out I had missed out the diodes! not saying its definiately that which is causing ur problems but its wortha look in that area.

[nunocaldeira]

Some types of foam that ship with electronics components are conductive. Don´t use them for isolation .

I had some headaches with a pedal because of this.


Check everything. Component values, board traces, solder joints, cables, guitar, amp...


Nuno

[petemoore]

  My dad used to say:
  "When all else fails, read the instructions"
  RG has written these out for you to use.
  Look in the thread that stay at top of list:
  "What to do when it doesn't work".
  Sometimes all it takes is a little diddling about, other times the debug techniques are the quickest way to an answer to 'what's wrong here'.

[Mark Hammer]

12pf will lower the rolloff in the op-amp stage from 15.9khz down to 13.3khz.  When you factor in all the harmonics that the clipping produces, the .001uf cap in parallel with the diodes to bleed high end to ground, and the typical rolloff of guitar amp speakers above about 6khz or so, I don't think you'll notice the change from 10 to 12pf very much.

That's the long way of saying that this particular cap change is not the source of your problems.

[6stringer]

It works!    I changed out the 12pf for a 10pf and also replaced C2, a .01uf cap that I thought was questionable with a new one.
Now it has a nice overdriven crunch.  Not the smoothest distortion I have, but usable.  I'm going to try it on my pedal board and see....
Do you think changing the diodes could smooth out the tone?  If so, what would you recommand?
Thanks everyone for all your help and advice.  I really appreciate it!
Robin

[delbowski]

hey..

yeah switching the diodes could be of some use for you.  check out
http://www.diystompboxes.com/wb/pages/build-your-own-stompboxes/stuff-to-read/simple-modstips.php
just kinda read down the page (the 8th entry is about changing diodes) and it will give you all sorts of little tips you can use to shape your sound.  you can even use a dpdt (on/on) to switch between diodes if you like.  hope this helps you out...

del

[$uperpuma]

for a smoother sound I used IN34a Germanium diodes, I am trying different things right now, I am using 1N914 - IN914 - L.E.D. and the distortion is great and took care of my volume problem, but the sound fizzles out at low levels, try try again, I guess...