several newbie questions in one post

[cakeworks]

several months ago, when i first became interested in diy effects (but knew about as much as I do now), I was looking on tonepad and found the distortion + by mxr, and I'd heard some good things about it and it had a nice, friendly, 'beginner' label on it so I printed it off and brought it to church to pass onto my mate to check out because he was also getting into it at the time. Well an older guy who works at a local television station, saw the pcb transfer shape on the sheet and walked up to us and offered to make the board for us because they had just rigged a new etching setup at the station and if we wanted something printed they could run it through for us as a 'test run'.

Well to cut an already long story short, it printed really well but it sat on my desk staring at me for three months, with all the parts sitting right next to it. Reason being, it had no holes, and i really had no idea that 1mm drill bits existed at the time, so i was quite annoyed. But today i was poking through DSE today and i came across a little bunch of packets with little tubes inside. I looked closer and realised that those tubes contained just the bits i needed. I promptly bought them and drilled the board when I got home. I'm just waiting for tomorrow to come so i can go and get some sockets and some decent wire so it doesnt frig up all the time like my last project did.

My questions are, however,

what clipping diodes do i use?

what on earth is a rev.log. pot?

and does the dist+ actually sound any good or is it just one of those crappy distortions that arent quite fuzzes and arent quite overdrives?

thank's once more

-Jack

[Mark Hammer]

Welcome to the road to ruin!  Lotsa great truckstops along the way!

1) The original used germanium type diodes, specifically 1N270 type.  For the purpose of this pedal, however, essentially any germanium type diode can be used.  The ones most commonly obtainable are 1N34 and 1N60 (there may be letter suffixes but these make no difference in our case).  This type will result in more clipping/distortion than some other types, given an equivalent input signal, but at the cost of some volume.  What many people have done is opted for silicon type diodes instead, such as the even-more-easily-bought 1N914 or 1N4148.  Because these raise the threshold at which clipping will occur, they result in slightly less distortion at full drive/gain settings, but because the clipping point is higher they end up producing a much louder/hotter output signal which you can then use to push your amp harder and generate some additional distortion at that end.  Some people prefer the one, some the other.  Some folks have instead switches on theirs to have their choice.  Since you indicate some reservations about pedals that don't quite make it to fuzz territory, I'd suggest you opt for silicon diodes since they can be easily purchased localy in all but the most remote locations.  This will still let you get a nice warm overdrive with lots of volume.

2)  Pots are described as having different "tapers".  This refers to how the resistance change is distributed across the entire rotation.  Roughly equal resistance change per degree rotation is a "linear" taper.  Resistance change that is logarithmic in its distribution so that small changes in resistance per degree rotation eventually become large resistance changes per degree turned are what you see described as "audio" or "log" taper.  because of how hearing works, these are often required to achieve what sounds like a gradual change to the human ear.  The basic idea is that the adjustment changes of interest to the user shold not be all bunched up within a few degrees of rotation.  If redistributing the resistance changes across the pot allow for no single portion of the pot's full rotation to have all the interesting stuff crowded in there, so much the better.

A reverse-log taper is one in which there are initially very large resistance changes per-degree-rotation, which soon settle down to much smaller changes.  Eseentially the mirror image of a log taper.  If the user is willing to simply wire a log pot "backwards" so that rotating the control clockwise goes from "more" to "less", then a log pot can sub for a reverse log one.

In the case of the Distortion+ (and this is about the 50th time I've written this, but that's not your fault), the use of a reverse log pot was necessary to get the pedal past the first, relatively useless, bit of resistance. The original pot is specified as being 1meg reverse log.  As it turns out, the first 900k or so of resistance change accomplishes very little in the way of changing the gain and tone, so a reverse-log taper gets you past that in a hurry, a bit like driving 90mph through farmland between cities so you can get to the "interesting parts" faster.  I have no confirmation of it, but my sense is that the designers were aiming for something that made sense in 1976 but not in 2006.  That pot can be easily substituted for with a 100k log or linear pot, with very little loss in functionality.  You will forfeit that ability to get a small amount of very slightly dirty boost in the first 30 degrees of rotation, but you will still have all the different flavours of distortion and higher gain available from the original, without the headache of having to score an exotic pot.  If you are aiming for authenticity, fine, but if you just want something that will work and give you interesting sounds, why knock yourself out?

3) I wouldn't describe the Distortion+ as any sort of holy grail of tone.  It's more like comfort food: one of those things you know you can always depend on to sound a certain way even though it is not awe-inspiring.  More importantly for you, it's simplicity and basicness of design make it a terrific platform for learning about how such circuits work and how to mod productively.  If your goal is to learn more about how to customize the other things you might own, building this will be a worthwhile effort on your part.

You've found the open door.  Might as well c'mon in.

[RaceDriver205]

does the dist+ actually sound any good or is it just one of those crappy distortions that arent quite fuzzes and arent quite overdrives?

Nah, its actually pretty good. I quite like mine. For such a simple style of circuit, it performs quite well, and its one of the 3 effects I have actually built two of.

what clipping diodes do i use?

I used BAT46 diodes (available at Jaycar), which I thought work pretty good. Alternatively you can use a germanium diode like the 1N60 or 1N34 (available at DSE). You can use any diode, but those sound the nicest.

what on earth is a rev.log. pot?

Its a special pot that you can't buy anymore, unless you shell out money for one from smallbearelec.com. Its not necessary to use one though. You can use a normal log pot, but wire it 'the wrong way round', or you can just use a linear pot.

Etching isn't to hard to get into yourself, either. All the stuff is sold at Jaycar, but the key tool required is a laser printer or copier.

Bet you'd think twice about actually buying an effect pedal in Aus tho, aye! $$$$$$

PB: ARGH! I just typed all this and it says Hammer got there first! Noooo! Oh well, for what its worth.

[petemoore]

  I wouldn't describe the Distortion+ as any sort of holy grail of tone.
  Great circuit
  'DIST' /  '+'
  DIST = Distortion
  +...must mean it is capable of boost, or that the dist is adjustable.
  Just two knobs, no switches, and uses diodes from signal path to ground to 'lop off tops off' the +/_ waveforms input, by shunting them to ground creating a different shaped waveform.
  It clips/compresses, it boosts.
  It can be used for this purpose.
  It can be made more 'Rat-like' [also a Diode to Ground Clipper], as in more versatile tone-wise by...adding tone control [like a Rat has].
  It *has become a DOD250, a Blue Clipper, and many other 'name/box/tones' using essentially the same two knobs and circuit board, chronology..I don't know exactly which came first, the board can be made to 'flavor' the Distortion to some extent, tastes vary.
  ..also, Because' it is simple and small, peripheral circuits may work well to make it more versatile and bigger.
  The 741 opamp has a fairly 'strong' flavor...utilization of this IC in the DIST+..well .. it's like '741garlic' or 'TLO82' onions...
  If you like the flavor of 741garlic, to get that, this ingredient must be available when cooking.
  If OTOH the TL082Onion is used, in some cases the difference between opamps is slight to non-discernable.
  In almost all other cases, most particularly in technical specifications, any opamp can outperform the 741. A great design in it's day and today, the balance between Opamp Distortion [or lack of slew rate or something like it consumes more power] gives a 'unique' distortion flavor or two I like.
  The + doesn't see as much time usage as some of my other distorters, but tweeked/~twist-tweekable   DIST+, BMP and FF entries are on my pedalboard for distortion flavorings, w/7band EQ, Mosfet Boost for now, and other efkt types.
  I put a variable LP Filter on the chosen Dist+ diodes, for thick mud w/Mosboost hammering input, it makes up nice'n'plenty, mushy meat 'n potatoes w/gravy that way, a fairly EZ recipe...don't forget to add fresh ground salt to taste.
 

[Mark Hammer]

Pete's right.  Although the venerable LM741 single op-amp has been eclipsed many times over by other better op-amps that have come out since the mid-1970's, and people at the service counter will more than likely say "Well this one will easily replace a 741" with the best of intentions, the 741 is the one the Distortion+ is designed around.  I don't doubt that you could make a different chip sound exactly the same by monkeying around with a bunch of the component values in the circuit, but to date no one has done so.  So, if you are going to build it following the posted schematic/project/layout, make sure to use an LM741.  It IS a lousier chip with poorer audio properties, but in this application it is ideal.  It's not like you are building a broadcast-quality studio mixer are you?   If push comes to shove and you can't find one, then simply install a chip socket in your pedal and use what you can find for the time being.  Then, when you eventually score one, you can replace it and hear the difference.

This tone control is a simple but useful addition to the pedal, although it will not sound "stock". http://img.photobucket.com/albums/v474/mhammer/SWTC.gif

Again, this is one of the reasons why the Dist+ provides such a great learning ground.  It lets you play with things like chip choices or add-ons and learn what differences they do/can and don't/can't make.

[cakeworks]

Wow, thanks for your help guys, Appreciating it!

would the switch look like this? That's to switch between silicon and germanium diodes.


I'm not sure if i'll put the tone pot in there, maybe on a future build.

Should be good, I'm gonna get most of the stuff done tonight. I'll keep you all posted.

Once more, thanks for your help.

[RaceDriver205]

Pete, are you hungry or something?

[Seljer]

Wow, thanks for your help guys, Appreciating it!

would the switch look like this? That's to switch between silicon and germanium diodes.

To switch between 2 completely different setups of diodes I'd do something like the one on the left here. You can really create a bunch of different setups to switch between different diodes (I just drew up the first things that came to my mind)


(the option of "no diodes" would give you no clippin, and only a clean boost..well kind of, depending on the rest of the circuit, I think the MXR Distortion+ has the opamp allready pretty overdriven)

you can go all the way and add in every type of diode you can think of and mess around with them to your content (look at http://www.beavisaudio.com/Projects/ScreamerLab/index.htm for an example, under the "Clipping Mods" section)

[GibsonGM]

I just boarded the Distortion +...have made a germanium fuzz face and a Big Muff, and I'm really liking this simple little ckt!   I used 1N914 diodes (try them, too!), and I'm driving the clean channel on a Fender Hot Rod Deluxe.  For the rock stuff I usually play (Clapton, some Jimi, Guess Who, Frampton etc) this pedal's going to be handy.   Much more mid content than the drive on my amp, good saturation and a warm tone. Extremely responsive to pick dynamics.    I didn't like it with the Ge diodes or LED's, too fuzzy for my taste.  This one's getting boxed this weekend and going on the board...

The D+ is a great for getting an all-around setting without dickering w/the amp and pedal settings...I could go from Aerosmith to STP with this little gem    Nothing bugs me worse than having to play with pedals for 4 minutes in between songs....infinitely and easily mod-able, too...

[cakeworks]

So would i do something like this for my switch?

<a href="http://photobucket.com" target="_blank"><img src="http://i3.photobucket.com/albums/y71/jcpaid4me/switch.jpg" border="0" alt="Photobucket - Video and Image Hosting"></a>

thats what i gathered from seljer's post

[cakeworks]

Just to let whoever cares know, I just completed the build and it's pretty cool. I much prefer it when the gain is rolled down a bit and it clips later rather than when it's right up. at the moment i'm using the silicon 1N914 diodes but soon i'll add the switch to choose between the germaniums and the silicons.

[Seljer]

So would i do something like this for my switch?

<a href="http://photobucket.com" target="_blank"><img src="http://i3.photobucket.com/albums/y71/jcpaid4me/switch.jpg" border="0" alt="Photobucket - Video and Image Hosting"></a>

thats what i gathered from seljer's post

that'd work fine

[GibsonGM]

That'd work ok, Cake...of course, you might want to put the diodes right on your board and hook 1 end directly to ground...it would be a little neater  But the principle is fine