new Formant book arrived

[Bjorn Julin]

>From: jhaible at t-online.de (jh.)
>Got the new Formant book today.
>
>First impression brings up a couple of questions:
>
>TL081's as noninverting buffers after 3080's in VCF.
>Should lock up due to phase reversal when heavily overdriven,
>shouldn't it ?

Not neccerily! I belive it just gets full and newer reverse,

>Heated transistor array for the VCOs. Adjustment by measuring
>the voltage drop over a be junction and emitter resistor. They say
>the voltage depends on the manufacturer of the chip - I'd
>expect it to be different for each chip, not just for each manufactuer.

I say:
It depends on the E resistor used in combination with VBE voltage
"and" Iref . It can be batch as well as individual and manufacturer 
dependent. I asume that they take the ref V from the emitter side.
What is the configuration of the heater? One array per VCO?
Standard Moog?

>Moog ladder with with single opamp buffer stage ... debatable.

I have done the same and its possible to get OK performance,
one needs to use AC coupling to the differential buffer stage.

By the way, does formant do one OPamp diff stage or dual OP
in buff config (out to minus)???? I was talking about one OP diff.

I have experienced DC lock in certain DC stages in a Moog ladder!

>But what's really bad about the Moog VCF article is the theory:
>They show an unbuffered symmetrical RC filter and say the
>transistors take the place of the resistors - way over-simplified.

yes , booo to the article writer!

>A lot of low current BiFet opamps (TL061) are used, mainly for the
>output stages. Why use the low current version here, but TL081's
>in the VCF's internal stages ?

? gofy designers?

>The nice old OTA-based 4pole VCF is gone. The tiny jacks remain.
>
>Still a lot of words about the quality a VCA should have - and still
>3080's used.

Hohahaa , NE5517!! Hepp hepp! :-)

English translation available?

BJ
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