I'm cool, I designed a distortion pedal!

[Hal]

Ok, well, not on purpose....just fiddling around...And i put in some diodes the wrong way on my breadboard, and poof!  Found something pleasing to my ears :-D

my description - fairly over the top fuzz with very nice compression/sustain capabilities.



the op amp is a burr brown...it works with a tl071 or 4558, but doens't sound as good, imho.  The diodes are all 1n914

[bazzwazzle]

diodes only go one way so i think you might achieve the same effect if you take out the wrong facing ones. Try taking ground out where the wrong facing one is. i think it never reaches ground (the current) because of the wrongly positioned diode.

[petemoore]

quote
 diodes only go one way so i think you might achieve the same effect if you take out the wrong facing ones. Try taking ground out where the wrong facing one is. i think it never reaches ground (the current) because of the wrongly positioned diode.
 wrongly positioned diode.> which one, they're labeld D1 D2 D3...
 
 Try taking ground out where the wrong facing one is.> I don't follow what your'e suggesting.

[strungout]

I got the feeling bazzwazzle is taking about D1. If so, actually the way D1 and D3 are serves to clip the signal from both sides, thus creating distortion.

[Marcos - Munky]

Do you have soundclips?

[Hal]

not yet, I'll make them soon...

[Paul Perry (Frostwave)]

I think the diode directions DO matter, particularly the relative dirtection of D2 & D3. And, I think the distortion characteristics will vary according to the load placed on the unit by whatever comes after it.
Good to see something new! Keep them coming!!

[bazzwazzle]

Yes D2 and D3 matter alot. But D1 is facing the wrong direction, so as far as i can comprehend it the current doesn't pass through it. So I'd think it would fine to take out D1 and it's connection to ground from the circuit, because the current never reaches ground due to the incorrect direction of D1. Give it try and see if there are differences or not. Never know!

[bazzwazzle]

actually i guess i'm wrong. Look here: http://www.diystompboxes.com/cnews/mods.html

the diode is positioned just like yours. That's odd to me though, how does it work since it's facing the wrong direction??

[Transmogrifox]

bazzwazzle-  D1 begins to conduct on the signal's negative half-cycle.  When you have a node referenced to ground and capacitively coupled to a voltage source, there is a short period of time (every half cycle) when the voltage at that node is actually negative with respect to ground, so current DOES flow from ground through D1.  This is what clips the negative half-cycle.

This diode arrangement is actually brilliantly interesting because it introduces a cross-over distortion effect as well as assymetrical clipping.

The only changes I would make to the circuit is to put a buffer on the output so the sound of the pedal doesn't change with different amps, and I would tie another 430k resistor between that voltage divider and the signal path to make the overall input impedance about 430k and put a cap in the divider to filter out power supply noise from the signal path.  These changes wouldn't effect the sound much, but would just make it a little more quiet and robust for use with different amps.  

A volume control may be worthwhile....tone stack...blah blah blah.  If it sounds good, why change it, eh?

GREAT WORK!!!  I think I'll build one since it looks quite simple to build and easy to use.  I'm excited to hear samples.

[Boofhead]

Although unconventional there's nothing wrong with the diode connection.  That connection just gives a harder sounding effect.
You may want to play with a resistor to ground say 100k-220k on the output so it behaves consistently on different amps.

[Hal]

bazz - a guitar's signal is AC - therefore current passes in _both_ directions.  Its something you need to read about, and think about until your head hurts.  Then do it again.

Transmorgrifox - thanks for the kind words :-D.  The buffer idea is very good :-D.  And I'm only using half of a dual op amp as it is, so It should be simple, too.  I planned on putting a filter cap in there, I already had one across +9 and ground, but didn't draw it.  Obviously, its missing a lot - like pulldown resistors, etc....

One thing i need to try is a 100k or 50k pot where the 390 ohm resistor is.  That should be able to effectively take the gain down to 2 (or 4)...It sounded ok in that range, but I wanted the higher gain.  A log pot might work well in this situation...

Also, i just put in the first output capacitor I picked up, and it sounded good....not sure if something smaller would sound better.  

Sorry I dont have sound clips yet, but I just scored a box of random electronic junk from a friend's dad.  This stuff is all from 1975, a "kit" for learning digital electronics...But real stuff, not a kid's toy.  A bunch of boards with all types of digital chips, but also has a function generator, power supply with -12, -5, +5, +12, and +170 outputs...switches and indicators blah blah blah.  

Also got a nixie tube "milivoltmeter" that I think I will be turning into a clock soon :-D
/rant

[cd]

FYI, here's what a sine wave going into the circuit above looks like:



I did a circuit sim using 1N4148s.

[Hal]

cd - thats awesome!  What program did you use?  I (obviously) used circuitmaker to draw it up, but couldn't figure out how to simulate.

[cd]

cd - thats awesome!  What program did you use?  I (obviously) used circuitmaker to draw it up, but couldn't figure out how to simulate.

I use Multisim (www.electronicsworkbench.com) - it's really easy to simulate, you just stick a virtual oscilloscope onto the end of the schematic (output) and get the output.

[WGTP]

I have used in-line diodes in different places, but it didn't occur to me to put them between the diodes to ground.  Cool idea.  I guess you could put another one in line before or after the diodes.  I find that GE's reduce the effect and have a smoother tone, might try one.  One other suggestion, replace one of the diodes to ground with an LED.  I like playing with diodes because of the variety of sounds and feels you can get with the different clipping thresholds.  

[Hal]

I have used in-line diodes in different places, but it didn't occur to me to put them between the diodes to ground.  Cool idea.  I guess you could put another one in line before or after the diodes.  I find that GE's reduce the effect and have a smoother tone, might try one.  One other suggestion, replace one of the diodes to ground with an LED.  I like playing with diodes because of the variety of sounds and feels you can get with the different clipping thresholds.  

i actually was going to try that soon - play around with different diodes.  I'll also try my Germanium/Shotkey/whatever the crap they are diodes there, and see how they sound :-D

[Paul Marossy]

Very interesting concept there. I wanna hear a soundclip, too.  

[Transmogrifox]

You'll get the best representation of what the circuit does to a pure sine wave conceptually if you take all of the caps out and generate a sine wave into a 100 ohm resistor feeding the diode configuration and probe the output.  Then after that, start adding parts of the circuit back in and simulate it each time and maybe at a few different frequencies to see what begins to happen.   Those tall-ish peaks come from the op-amp clipping, then the high-pass effect of the 47nF cap passes the higher order harmonics added by op-amp clipping.  Then when the last diode opens, the capacitor quickly discharges to another level.  The 1uF cap creates a similar effect on the lower half-cycle.  

As you can see, the filtering effects the waveform drastically (this is why it makes such a big difference in the sound), but the conceptual clipping of that diode configuration is best seen without the capacitors.