Albert Petrak writes:

> I'd be pleased to have comments and suggestions on the information
> about Artrio-Angelus, and indeed on the notion of transfer of
> expression codes in general.

I once owned some Angelus rolls, which I enjoyed playing on my Duo-Art
using manual expression control, before selling or trading them.  When
I studied White's little book (Vestal reprint) long ago, "Piano Playing
Mechanisms", I learned some interesting things about the Angelus
system:

1. Like the Duo-Art, it uses Theme and Accompaniment, with "snakebite"
Themodist holes to switch either or both keyboard halves to the Theme
suction.

2. Like Duo-Art, the expression coding is purely "digital" levels, no
"analog integrators" like the Welte or Ampico.

3. Unlike the Duo-Art, the Accompaniment regulator is in series tandem
with (downstream of) the Theme regulator.  Thus, Power 3 on the Accomp.
means "3/8 of whatever the Theme is doing."

4. There are 5 holes for 32 levels of Theme, twice the Duo-Art's
resolution.  The Accomp. has only 3 holes for 8 levels, but since these
are relative to the Theme level, that's plenty.

5. The Angelus regulators operate by translating the roll perforations
to establish a reference vacuum level, which then controls the large
regulator pneumatic.  Similar to an Ampico B regulator, but using a
conventional pneumatic inside the reference chamber, not a membrane.
Very ingenious and quite simple.

6. Unlike the Duo-Art, the Angelus requires a vacuum reservoir with the
pump, since the Angelus regulators don't store energy like the D-A's.

Most of the above I deduced from diagrams in the book.  I'd appreciate
corrections from those who've actually rebuilt an Angelus.  It seems
to me to be a superior system, though how it worked out in practice
I don't know.

Mike Knudsen