General Info Question: How To Choose An IC

[railhead]

I just built my first effect with an IC (a Red Llama clone), and that got me thinking in generalities: how do you know which IC to use? I'm sure this is a totally ambiguous question with a million different answers, but seeing as how there are thousands (millions) of different ICs out there, how do you know which to try and goof around with when experimenting with a distortion or overdrive or anything else? What do you look for?

I guess the "want-to-know-why" part of me isn't satisfied with seeing a schematic says to use a CD4049UBE (or whatever it calls for) and just doing it. I'd like to know why -- when the circuit was designed -- the designer chose *that* IC as opposed to another. What did you look for?

Thanks for any thoughts/insight.

[boogietube]

That's a can of worms!
Some are selected for their tone (LM308-Rat, JRC4558-Tube Screamer), some are selected for their low noise operation (NE5532, TL072),  some are selected for both low noise and low current draw -example - the NE5532 is pin compatible with the TL072-the NE5532 is lower noise, but higher current draw-the TL072 is higher noise with lower current draw. Higher draw kills a battery quicker.
Special function IC'S are selected for their function-PT2399 Echo IC etc..
There's a lot of info here on this subject-Search and Learn!
Hope this helps!
Sean

[railhead]

I guess what I was more getting at, is if I want to pick an IC for distortion, how do I now what to look for in an IC? Will a spec sheet tell me how much gain I can squeak out of it? What do I look for?

[petemoore]

I guess what I was more getting at, is if I want to pick an IC for distortion, how do I now what to look for in an IC?
  Will a spec sheet tell me how much gain I can squeak out of it? What do I look for?
  The gain is often limited by a 9v supply...
  As far as distortion, look for clipping diodes/voicing .. or harsh distortion from just an opamp. Not to say that's set in stone, but getting good sounding distortion from a standard opamp clipping [running out of room to swing the signal voltage because of power supply limitation] is tricky at best IME.
  Getting a nice sounding distortion from regular opamps is something I gave up on, I have a RAT with diode lift, and that does work as a dirty booster.
  Then there's CMOS, and they do clip easier by a great margin than a standard opamp type. Soft 'tube-like' or 'tube type' distortion names and sounds abound with the CMOS distorters. They can sound alot like a tube amp output distortion, I need to build another CmOS circuit and try to keep it working. 

[R.G.]

First, you have to know what you want.

Find and buy or borrow (i.e. library) then read "Audio IC Opamp Applications" by Walt Jung.

Then look for the selection guides in manufacturer's web sites. If you've understood the book, you will have no trouble picking. The book will tell you what parts of the spec sheet you need to look at.

That is also a gross oversimplification. Until you know what you wished your circuit did, and also what factors of the opamp have some bearing on that, you can't make a rational choice. Maybe a better answer is read. Everything. All the time. As a habit, I read textbooks, technical articles, techie books and so on for about 2-3 hours per day, and have for over three decades. Some days more if I get a chance ... 8-)

[petemoore]

  Will a spec sheet tell me how much gain I can squeak out of it? What do I look for?
  Yes.
  Textbook Opamp distortion.
  Will distort in some ways like a tube would, as in onset of distortion will be stronger at the signal peaks, the signal peaks will be limited, that's about where the similarities end.
  Opamps will tend to put spikes in the waveform at the onset of distortion.
  The sound can tell you somethings about understanding what's what, wire up an opamp for high gain, boost the AC signal input source, or drop the power supply DC voltage to make it distort by running out of headroom...try different opamps, some distort more gracefully than others.   
  Take a look at 'Black Cat' distorter, or built a Dist+ or Rat or TS...any opamp distorter, pull the clipping diodes...see what you get.