Favorite designs

[Tony Clark]

> Not real sure if the necessary +3300ppm temperature resistors are 
> still around.

   I believe they are.  There have been a few posts for companies that 
have such beasts.

> The original Moog VCOs are VERY drifty. Any transistor, by default, 
> is an exponential generator. But the temperature dependance of the Ies 
> term (not the kT/q term, although this is a small contributor) makes 
> any EE cringe. Heating up the transistor (like the uA726 does) is  not 
> really solving the problem.

   No, it may not completely solve the problem, but it does prevent long 
term drift in the oscillator.  For instance, my OB-Xs use a method 
similar to the National's AN-299 temperature compensation linear voltage 
to exponential current generator.  Sure for the first 5 minutes or so the 
oscillators will drift, but once they are warm, hit the autotune button 
and never have to worry about them drifting again!

> I really encourage everyone get a copy of Wendy Carlos' 
> CD "The Secrets of Synthesis" (I found mine at www.cduniverse.com) and 
> listen VERY CLOSELY to what she is saying. The message is: A Moog is a 
> Moog is a Moog. And I beat that dog to death. 

   This is a great CD!  Picked mine up at Barnes & Nobles.  The only 
thing I was disappointed in was the fact that she didn't explain her 
alternate tunings!
 
> 3) For envelope generators, really can't beat a CEM3310 + a 555 for 
> variable gate delay. 

   I haven't seen any good discrete envelope generator schematics yet 
unfortunately.

> 4) For VCAs, really can't beat a CEM3381/3382. The OTA approach 
> (CA3080/LM13000) are just too noisy. Cheap, but noisy. Why build a whole 
> modular and run it out of a 45dB SNR part??? The CEMs have 100dB SNR! At 
> least use MAT-04 matched transistors for the front end. 

   The VCA in the MAT-04 datasheet is rather nice.  It doesn't take much 
modification to get it VC'able to modular standards.  It boasts a SNR 
about equal to the CEMs.

> 5) For op amps: use AD or Linear Tech parts. The TL07x parts are just 
OK, there are MUCH nicer parts. Rule #1: ALWAYS use dual, NEVER use 
quads. Why? All of the really cool parts are duals, and quads crosstalk 
too much (If you really need a quad, use the AD713KN. Awesome!) For 
duals, look at OP275 or LT1113CS8. Stay away from junk like 1458s. Think 
of a TL072 as the BOTTOM rung of the food chain. 

   Shouldn't be any reason to avoid quads for DC-low frequency designs.  
Crosstalk is also usually less than your noise levels anyway.  For audio 
signal paths you might want to avoid quads unless you are chaining all 
four op-amps in series or using it to mix signals down to one path.  I 
wouldn't use it for channel separation.

> 6) The single most overlooked component is the power supply.

   I agree!

> 7) The Electronotes series is simply the best way to get all the 
world's knowledge of synth design. Call Bernie Hutchins 9PM to 11PM 
Eastern time at 607-273-8030. At the very least, get the "Preferred 
Circuits Collection". Then, save your money for the $265 (I think) "full 
set" which is about 2000 pages. 

   I've heard it's probably the best for getting started.  Especially if 
you don't know much about electronics in general.  But don't just limit 
yourself to old designs.  There's still room for great new circuits to be 
designed, especially since the level of electronics has advanced far 
beyond what was available 20 years ago.

> Please, no "your the CEM chip guy" flames. Yes, I am. But I'm also the 
> "former Moog designer with 20 years experience designing this stuff" guy.

   No flames here.  :)

   Tony

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I can't drive (my Moog) 55!
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Tony Clark -- clark at andrews.edu 
http://www.andrews.edu/~clark
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