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[jhaible]

		>sorry, but this is completely wrong.
		>And how does it work ?

The transistors are connected as diodes. So, unlike
the Moog ladder, you don't have buffer stages between 
the individual RC filter stages. Each stage is loaded
by the following stage. So in the  interesting region above
the cutoff frequency it has a slope of (approximately) 
18dB/Oct. The wording "18dB" appears  in the  service 
manual of the EMS VCS3 / Synthi A (which also uses a 
4-pole diode ladder filter) and it describes the typical 
behaviour of this kind of filter fairly well. It's quite
different from a Moog filter not only in topology, but also
in sound. That's all there is about it.

At least from the technical point of view. 
But then there were the journalists, and the competition of 303
clones. With wannabe experts sharing their "wisdom" about
the original being a "24dB filter", or even a "3-pole filter",
each and everyone could market their garden variety VCF as
"close to the original", and take advantage of all the confusion.
With those companies who actually built true clones (like MAM
and a few others) being cheated.
 
> (You have this from the infamous "Doepfer interview" in KEYs, 
> don't you ?) 
> Yes ! 
> 
The story behind this "Doepfer interview" is remarkable.

(1) There was some talk in one form or the other (we can not know)
between Doepfer and a KEYS journalist.

(2) KEYS prints an "interview" with Doepfer. Doepfer is quoted
with the statement that the 303 filter is just a Moog filter with 
unselected transistors. To back this up, they print parts of both
schematics. If you look at these schematics, you can clearly
see the main difference: transistors connected as diodes. Only
a small minority will notice. The masses read the subtitle "No
Difference" and will make their decision what 303 clone to buy.

(3) I'm calling Doepfer as soon as I read this article, and big surprise:
He says there was no interview at all, KEYs have just put some
bits of general talk together and present it as "interview". Big
surprise #2: Doepfer does not know that there is a difference
between the filters at all. He has examined, and simulated, the Moog
cascade, but not the Diode ladder. He does not claim to be the
"expert" KEYs has made of him.

(3) I'm writing a reader's letter to KEYs (not a friendly one, admitted).
They should at least correct this misinformation in one of the next
issues. No response nor reaction at all.

(4) Meanwhile other people must have complained, too. There
finally *was* a correction of - and apolgy for - this misinformation.
It did not appear in KEYs, however. It was printed in the AME
Journal, a small member's publication of the Arbeitskreis
Musikelektronik, so 500 people could read it. There was some
lame excuse why it was not corrected in KEYs, too.

(5) You guessed it: Doepfer's 404 was one of the "clones" that
had a standard 24dB filter. Why should he want to correct
a misinformation, when it helps selling his instruments ?

Most probably I put more into this story than there really is.
My friends who put a real 303 filter into their product 
have probably sold more 303 clones than anybody else, 
(and I surely do *not* speak for them here).

What I cannot stand is the attitude of this magazine that
pretents to be "the experts" (for analogue, and for each
and everything), hardly has printed an article on analogue
topics without severe technical errors thru all the years
(How many people have "learned" how Soft Sync 
"really works" from KEYs ?), and who has not the guts to
admit and correct errors that it has spread to the public.

JH.

(I promise this will be the last of angry posts to the list
for a long time (;->).)