Introduction: *NOT* Like a BOSS Distortion

Tired of the same old Boss-like dual-diode-clamp distortion pedals?

Want a pedal that offers truckloads of enraged guitar brutality, downright to the border of the obscene, yet is also capable of a mellow bluesy overdrive?

Want a stompbox that lets you tune what the distortion sounds like, instead of just having the choice between 'crappy' and 'even crappier' ?

Then this pedal is for you.

WARNING:Unconventional circuitry ahead

The *Not*-Like-a-Boss-Distortion pedal uses a transistor based nonlinear cell, that lets you tune the shape of the distortion.

I'll explain how to build the pedal, how the circuit works so you can impress your friends, and hey, just because you clicked and read this instructable, I'll even throw in some tips on how to customize this pedal to make it even more unique! I'll assume you have some experience with pedal/circuit building. If anything is unclear, feel free to ask.

Read on...

Step 1: The Circuit

Conventional anti-parallel diode clampers are limited in that the shape of the distortion is always the same. I've seen some pedals that try to solve this by letting you switch in several different types of diodes/leds, but it's still kinda limited. This pedal makes use of a unique nonlinear transistor circuit (Q1 and Q2), that allows you to control the shape of the distortion anywhere from shallow saturation to a hideous non-monotonic response. How so? the input stage, U1a is simple amplifier of which the DC bias and gain can be controlled, nothing special there. Observe that the nonlinear cell is symmetric around the point 'a', which is DC halfway the supply by U1b, so to understand how this works, it suffices to look at the upper half (Q1, R8, R9, R12 and R18). Suppose the wiper of R12 is completely turned to the right. Then R8, R9 and Q1 form what is known as a 'rubber zener': Q1 would then be a pretty good clamp, where it not for R18, which makes it kind of a bad clamp. Which is a good thing if you want soft distortions too. Now, if the wiper of R12 is turned completely to the left, then we get a nifty non-monotonic 'bump' like response. This means that for small voltages, the output voltage (collector of Q1) will follow the input voltage. Once the input voltage is high enough (0.6V on the base) to switch on Q1, the output will start dropping with increasing input voltage. This leads to a 'bump' response: really shreddy sounds. So the 'shape' pots allow you to tune the upper and lower distortion shapes separately, while the 'bias' setting allows you to choose where in the nonlinear function your 'zero' or resting point is. The tone and volume level control are just that: a simple low-pass tone and output level control. The oscilloscope screenshots give some idea of what is possible.

Note that the nonlinear transistor cell is not completely symmetric: R18 and R19 are unequal. This was done on purpose to give you more options.

Tip: tune R18 and R19 to your own liking, or even better: replace it with another variable resistor to have even more freedom.

Bonus Tip: replace R8 and R9 and likewise R10 and R11 with a pot, wipers going to the bases of Q1 and Q2 respectively. Obviously this won't fit in a 1590B anymore.


TL;DR: This circuit is awesome. I wish I paid better attention in 'Circuits 101'.

Step 2: Build the Circuit

The circuit can easily be soldered on a piece of perfboard. Incidentally, transistors Q1 and Q2 can be replaced with any type of small-signal transistor. Same goes for the TL072 JFET input opamp. No special component needs here.

Step 3: Build the Enclosure

The circuit is housed in the popular Hammond 1590B enclosure. I made the design for the front in Inkscape. The 'bossy' looking character is something that floats around on the internet. You can easily adjust the design (.svg) to your own needs if you are inclined to do so.

The steps to preparing the enclosure are the same as here:

https://www.instructables.com/id/Screaming-EX-Boos...

Here's how it goes:

  • print the design on paper, cut out and tape to the enclosure,
  • mark the positions for the holes with a sharp object and a hammer,
  • drill the holes, use safety gear for ears, eyes and hands (I mean it!)
  • be careful with the position of the power jack as the pots are partially underneath it,
  • clean the enclosure, spray-paint it with a few layers of paint (this takes some practice),
  • print the design on transparent label paper, cut out and stick on the enclosure. be sure to avoid air bubbles,
  • apply a few layers of clear coating,
  • stick some rubber feet to the lid.

Step 4: Assemble the Pedal

Almost there!

Next assemble the pots, switch and connectors. Solder short (10cm, 4'') leads. I got these from a local dealer.
Be careful not to scratch the paint.

A piece of plastic from a soda bottle was cut to size and folded around the circuit board to protect it against shorts.

Place a small schematic printout in the enclosure. This will come in handy if you have to repair it some day.

That's it. Marvell at your creation!

Be sure to let me know your results if you build the NLABD.

Have fun!

Comments

author
kidwidget (author)2017-08-29

Can you post some audio or a link to a video?

author
Kajnjaps (author)kidwidget2017-09-03

I don't have a good microphone at the moment, but I'll look into getting one (suggestions on type/brand are welcome).
Also, some additional info on this circuit can be found at: http://www.madbeanpedals.com/forum/index.php?topic=25587.0

All the best!

author
miketguitar (author)2017-05-27

found this on Reddit: http://www.taydaelectronics.com thanks to r/diypedals for a component source, they do have poly film caps (gum drop).

author
miketguitar (author)2017-05-22

Ok, thanks I know of digikey.com and mouser.com in the US, I was looking for links; specifically for capacitors, it's kind of hard to find gum drop caps unless they are overpriced.

author
Kajnjaps (author)miketguitar2017-05-22

"Gum drop" caps. Had to google that one :-). You can use ordinary ceramic and electrolytics here. Or salvage from electroscrap of you really want to go cheap.

author
miketguitar (author)Kajnjaps2017-05-22

Yeah - gumdrops are film caps typically dipped in a plastic coating to prevent corrosion, and praised for their "superior" tone, but used mostly for their reliability and lifespan - the leakage is very low and the components will be very precise in terms of capacitance will with little bleed in that capacitance - probably little difference between these and other film caps, but generally gum drops are used for guitar pedals. There are pedal part specific retailers as well (For those of you looking to become a pedal building hobbyist):

http://smallbear-electronics.mybigcommerce.com/

http://www.pedalpartsplus.com/

https://buildyourownclone.com/

Very good instructable btw, I'm looking forward to building it. -Cheers

author
Oncer (author)miketguitar2017-05-24

Actually if you try bigger outlets like RS, CPC, Farnell or Rapid you can get polyester film caps quite easily and in hobbyist numbers i.e. half a dozen or even one. Just check what multiples they are sold in but most places will sell one or small multiple of through hole passive components. Tell them I recommended them and they will go "Who?". By the way try gooooogling for "tropical fish" caps.

author
Kajnjaps (author) Oncer2017-05-25

Lol, "tropical fish caps"

Never realized my Cardinal Tetras were 0.62pF.

:-D

author
Kajnjaps (author)miketguitar2017-05-23

Thanks! Good info! I usually just go with what parts I find in my drawers.

Be sure to post an "I Made it!"

:-)

author
EpicElrod (author)2017-05-22

Great job man! This is the best distortion pedal I've seen on here. I want to hear it in action.

author
Kajnjaps (author)EpicElrod2017-05-23

Thanks! Might do a video in the near future ;-)

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