Favorite designs

[Paul Schreiber]

I'll take a stab.

1) For VCOs, really can't beat a CEM3340. Extremely well behaved, excellent tempreature tracking. Designs using uA726s should be avoided at all costs (can't get uA726s at all for <$200). Not real sure if the necessary +3300ppm temperature resistors are still around. Probably best bet for a new discrete design would be a VCDO. Although not necessarily "DigiKey friendly", it skirts the temperature issues (and introduces a few quirks of its own). It really depends on the cost vs quality. 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.

2) For a VCF, no contest: Moog ladder filter. If you can't beat 'em, join 'em. The CEM3328/3378 comes close, but really there is no substitute. Now, the "downfall" of a Moog is just that: it's a certain sound associated with synthesizers. ARPs sound like ARPs. Most Oberheims sound the same. The particular "sound" of a synth is 95% in the filter characteristics. 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.

3) For envelope generators, really can't beat a CEM3310 + a 555 for variable gate delay.

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.

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.

6) The single most overlooked component is the power supply. Remember, ever the lowly LM7815 was not around for the first analog synths. For really good designs, check out the Audio Amateur Magazine (603)924-9464. Folks, this mag is REQUIRED reading for all DIYs. Since the somewhat demise of Electronotes, this is really the only source of precision analog design. Stereos and CD players share alot with synths. For a really good design, the 3 terminal stuff is NO GOOD. Perhaps I can address this later.

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.

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.

Paul Schreiber
Synthesis Technology

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From: 	Steve Jones[SMTP:sj2393 at ansys.com]
Sent: 	Thursday, April 17, 1997 3:53 PM
To: 	synth-diy at horus.sara.nl
Subject: 	Favorite designs

Foregoing the hotter flames, what are some of our favorite
designs here for the various analog modules.  I know this
is an incredibly general (and perhaps dangerous) question.
But I'm currently at square one and I'm trying to plot
out a course of action.  Modularity and flexibility are
definite criteria.  So is frugality.  My plan is to procede
incrementally, maybe starting with a single VCO and adding
pieces as I go (sound familiar to anybody).

I have been encouraged by some to leave the CEM chips to
those that really need them.  That sounds reasonable to me;
so what are some discrete designs?  Gimme shematics! 8^)

This is indeed a general question.  But since there is no
FAQ file per se, it certainly is, if rudimentary, on topic
(or nothing is).

One more, slightly more specific, question: what is the
difference between hard and soft syncing (surely a FAQ
candidate)?

thanks, you guys are so cordial to beginners like myself,
steve