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<DIV><FONT size=2 face="Trebuchet MS">
<DIV><FONT size=2 face="Trebuchet MS">Hi Michael. </FONT></DIV>
<DIV><FONT size=2 face="Trebuchet MS">As far as I know the scheme is complete
and correct.<BR></FONT></DIV>
<DIV><FONT size=2 face="Trebuchet MS"></FONT> </DIV>
<DIV><FONT size=2 face="Trebuchet MS">The DC coupling was a deliberate design
decision. According Rossum in the EVOLUTION's brochure "I Envisioned to
DC-coupled design with a cutoff frequency range well beyond 10 octaves, as well
as variations of the height Eliminating of the resonant peak oscillation
amplitude or frequency with voltage control".<BR></DIV></FONT>
<DIV><FONT size=2 face="Trebuchet MS">The nominal level of 20mVpp pursues a much
lower distortion than usual in moog ladder filters. Again Rossum says "The 1100
used a Moog ladder as ITS core element, but I wanted to isolate the audio innate
characteristics of the ladder filter from colorations resulting those from
the input level-shifters and output amplifier used in the Moog
904A".<BR></FONT></DIV>
<DIV><FONT size=2 face="Trebuchet MS"></FONT> </DIV>
<DIV><FONT size=2 face="Trebuchet MS">Regarding the 1100 output stage, Dave says
"I then a designed a completely new output stage for the ladder; esta circuit
has never (to my knowledge) Been used outside my designs The entire signal path
was DC coupled and the resonant feedback. path phase compensated. The 1100 was
my favorite sounding filter (I liked it more than the SSM2040 I later invented,
and kept the 1100 as E-mu's modular lowpass in preference to a cheaper 2040
design). The operational range of the cutoff frequency was from 0.1Hz to 25kHz
acerca, with Q's stable throughout. "</FONT></DIV>
<DIV><FONT size=2 face="Trebuchet MS"></FONT> </DIV>
<DIV>You say <EM>"The filtering action is based on the emitter resistance which
is set by DC bias"</EM> Partially agree. The filtering action takes place by
varying the current through the PN junction, not the voltage on it.</DIV>
<DIV> </DIV>
<DIV><FONT size=2 face="Trebuchet MS">Pure technical curiosity, but I find
fascinating some aspects of this circuit...</FONT></DIV>
<DIV><FONT size=2 face="Trebuchet MS"></FONT> </DIV>
<DIV><FONT size=2 face="Trebuchet MS">Cheers, </FONT></DIV>
<DIV><FONT size=2 face="Trebuchet MS">Juan Bermúdez Costa</FONT></DIV>
<DIV><FONT size=2
face="Trebuchet MS">Barcelona</FONT></DIV></FONT></DIV><br /> <table style="border-top: 1px solid #D3D4DE;">
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