Designing Pedals

[jeroen_verbeeck]

Hi,
I've built and modified several pedals of mine, mainly distortion, but none seem to actually nail the sound I'm looking for.
So I thought "why don't I design my own pedal ?", but the thing is, I don't know how to start.

How does one go about designing his own pedal ? How do you choose from all the parts available ?
Can someone help me with this ?

[Mike Burgundy]

Check out all the links available here on opamp and discrete design, do a search for opamp/filter/calculation/formula/theory etc in various combinations.
The best way IMHO to start is to take building blocks from existing circuits and tinker with those, orr combine them in different ways.
Opamp circuits are the best route to take, since they are the most predictable, and the math is easy. TL07x's have FET input stages, so the input impedance is high which is good for our purposes.
Start out (on paper) with the different blocks you'd like.
For example:
input cap=HighPassFilter(HPF)-diode feedback clipping stage with LPF-tone control-volume
The input cap provides DC blocking and acts as a HPF together with the next stage's input impedance (roughly the input impedance of the opamp). The value of the cap determines how much lows are getting into the clipping stage. Less lows *before* clipping often makes for better distortion and *more* lows after if you get it right. There's some calculation here, but you can also go straight to the "I wonder what this does" stage. Fine too.
Diode feedback clipping stage: take that straight from a tubescreamer. The caps in there tailor a bit of the sound, tame the highs a bit and such. See if you can figure out what tey do, and experiment with values.
Select a nice tone-control. There's a lot of good ones floating around here. Maybe add some extra LPF (LOwPass) to get rid of some of the higher harmonics (Fizz). Some say the real trick to good distortion is pre-and post filtering. There's a big truth in that.
volume pot, done.

Now you still have to make the opamp happy. Make sure all inputs and outputs float at 1/2V, and are isolated from ground or pots. Steal this from a TS too. Include other good housekeeping things (input bleeder resistors, etc. Nick this from existing stuff too, and have a look at GEO's effects wrapper)

Get yourself a breadboard, and experiment away! Rarely does anything sound great the first time you build it, so swapping parts on a breadboard is brilliant!
Start with simple stages, get them working, then add filtering, more stages, inter-stage clipping, some gum you found under the desk, whatever makes it sound cool, good, or ugly in an interesting way.
Have fun

[petemoore]

  Get yourself a breadboard, and experiment away!
  And experiment you will...If you're like me, calculating is done by 'alterations'.
  You'll probably skip trying to design an entirely new gain stage.
  And maybe alot of what the data sheets show is already 'filtered into' already existing stages, you can *Use [note I didn't say rip-off]...lol.
  There are plenty of existing designs to look at which utilize components to the extremes of 'normal operating parameters' and beyond.
  Here's some Gain Stages
  Bipolar
  Jfet
  Darlington
  Mosfet
  Inverting OA
  Non Inverting OA
  2Q feedback amp [fuzz face]
  Mu amp [jfet]
  I would imagine an emitter follower stage could be made from these, not too sure about a FF, these are nice for matching impedances and driving tone controls to min. or eliminate volume drop.
  Gotta run, Ill BB.