Regenerative Suction Regulator
& Hupfeld Animatic Clavitist Rolls
by Richard Stibbons (MMD 01.01.12-14)

A regenerative controller is one which over-compensates, either by design or accidentally.  Richard describes a regenerative suction regulator which evidently increases the suction in the action stack as more notes are played.  This behavior is in stark contrast with the Duo-Art stack regulator which supplies less suction as more notes are struck together in a chord.  -- Robbie

From: (Richard Stibbons)
Date: Mon, 8 Jan 2001 17:06:38 -0000

Subject: Regenerative Suction Regulator

Dear MMD,  I once owned a coin operated Hupfeld cafe piano which had
an intriguing label on the pump.  It read: "The pump must make 70
revolutions per minute.  More revolutions will cause disturbing noises
and less revolutions will impair the expressions"

The latter comment was interesting because the piano was no more than
an electrically pumped 88-note player with a simple stack regulator and
a pair of theme valves.  The reference to "the expressions", therefore
seemed a little optimistic.  When it was given to me in 1960, the
instrument was untouched internally, the motor having burned out in
the early 1930s.

All it needed was a new motor and for the heavy hoses to be replaced,
whereupon it sprang to life, playing well and, to my astonishment,
producing quite considerable expression.  Doubting my ears, I put a
gauge on and the vacuum was indeed varying between about 8 and 24
inches water column.  This turned out to be due to deliberate
over-compensation in the stack regulator, achieved by using a weak

The effect is familiar with wind motor governors which, if the spring
is too weak, actually slow down as you pump harder.  Applied to the
stack regulator the effect causes the piano to play louder as the
demand increases.  Therefore, crashing chords really do crash and
single notes play softly.  This is entirely appropriate for the "Bier
Keller" style of music this piano was designed to play.

I still have a roll which came with it which I recently scanned
and then wrote a simple expression program to emulate the effect.
(Hupfeld.mid attached).

To most ears, 1920s German pop was not great music but the result is
interesting, especially when viewed in Cakewalk or a similar program
which shows the note velocities.  It was obviously arranged with the
deliberate intention of creating 'the expressions'.  There is no soft
pedal, all the expression comes from the 'velocity versus demand'
effect described, enhanced only by the theme perforations.

The technique is very clever by virtue of its simplicity,
characteristically Teutonic, but it could easily be missed in
restoration.  I've always wondered if it is widely known about
and used in other instruments ?

Richard Stibbons
Cromer, England


From: (Richard Stibbons)
Date: Tue, 9 Jan 2001 09:49:07 -0000

Subject: Hupfeld Animatic Clavitist Rolls

Hi Robbie,  The piano in question came into this country in the early
1920s.  Unfortunately, this was a time when all things German were
somewhat unwelcome here.  As a result, Keith Prowse who marketed it,
went to some lengths to conceal it's country of origin.  It was badged
"Keith Prowse, London" and it was only the "LH" logo cast into the
frame which revealed it's true identity to the initiated.

The piano was an Animatic Clavitist identical to that shown lower
left on page 434 of the Bowers' Encyclopedia, "Animatic Clavitist with
orchestra cabinet."  It was capable of driving a bandbox, having a
multi port connector block near the wind motor, but this optional extra
had never been purchased.  There was a switch in the spool box which
turned the band box on and off.  It would probably have had about 12
small pipes and bass and snare drums.

I have two rolls which belonged to it, both with three tunes.  They
are very high quality and clearly German made.  The MIDI file I sent
you doesn't have the band tracks although it does have a mandolin
track.  It has no markings of any kind at either end.  The other roll
carries a Keith Prowse typewritten label.  The label is now illegible
but the middle tune is "Red Red Robin".

The rolls are very interesting because they use both square and round
perforations.  They were either made on a very sophisticated perforator
or were the result of a 'double pass' process.  I presume this technique
was another way of achieving a degree of expression. I don't know how
much is known of this process.  I can make a pictorial scan of a
section if you're interested.

The second roll has band box perforation tracks but, as far as I can
tell, no expression although there is a soft pedal track.  I can scan
it for you if you wish but I haven't written a program for reproducing
the band parts and it's hardly worth doing so for just one roll.  I
sent you the simple roll because it was a less confusing demonstration
of the point I was making.  As I said, I have long wondered if this
clever technique for generating expression is known about amongst the
modern fraternity.

There are three tunes on the roll I sent.  The first one is damaged
but the tune is "I Wonder where my Baby is Tonight".  Like you, I
recognized "Always" but not the third tune.

This was an extremely rugged and well-made instrument, and one of the
best things about it was that it lived from new in the front parlor of
a child-free private house.  There's a poignant story behind the fact
that by 1960, it was still "as new".  It was unmarked and untouched
inside and out and still had the original beaded lampshades.  Even the
open mercury dashpot switches were filled and working!  Like much of
my collection, it had to go when I moved house and I passed it on to
a small museum in Southern England.

Best wishes

Richard Stibbons


From: (Richard Stibbons)
Date: Thu, 11 Jan 2001 10:25:05 -0000

Subject: Regenerative Suction Regulator

The interesting correspondence from Tom Jansen [010112 MMD] tends to
confirm my theory that modern experts have lost sight of this clever
yet simple technique.  It is, after all, merely a matter of adjustment
of the regulator spring and few restorers or technicians would leave it
unusually weak unless they were aware of this idea.  I trust you will
agree this effect is not a figment of my imagination.  I was quite
surprised at the expression which appeared when I wrote this
experimental software.  The program is very primitive yet, musically,
the results are a big improvement.

I am in no doubt that Hupfeld used this technique in a deliberate and
controlled manner but have always wondered if other manufacturers
around the world also knew of it.  I have processed scans of some of
the more boisterous QRS rolls using the same algorithm and they
certainly produce expression which is, in most cases, an improvement
on the "constant volume" sound.  Is it possible that US manufacturers
might have used the same trick ?

The discussion about the Animatic Clavitist is another issue.  I was
never certain what was inside the "orchestra" box and a xylophone does
make sense.  The scale is well documented and I attach a scan of what
is probably an "S" roll.  My piano had the ingenious mandolin system
mentioned and also used pneumatic logic gates characteristic of
Hupfeld.  For example, the "motor off" track cut the motor but, when
opened in combination with the "soft pedal" a special latch operated
which initiated reroll.

One aspect which neither of your experts mentions is the use of square
and round punches on the same roll.  This would have been a major
manufacturing complication and there must have been a good reason for
doing it but I wonder what it was ?  I attach a pictorial scan of a
small section.  These rolls are fully of mysteries.  The use of the
themes is surprising in the musical sense.  In addition, many of the
"snakebites" are out of position.

Having examined the rolls more closely, I'm beginning to revise my
opinions about the quality.  Physically they are superb but there are
several bouts of "lumpiness" in the tempo and this, together with the
misplaced themes, makes me suspect that these rolls are copies which
might be several generations old.

I attach (1) a pictorial scan of part of one of the rolls; (2) a MIDI
file of one tune; all tracks are intact, only the webbing has been
removed; (3) a MIDI file as above but processed with my algorithm
which increases volume in accordance with an estimation of the vacuum
demand at any instant.  The control tracks have been removed.

Best wishes

Richard Stibbons

stibbons_Hupfeld.mid (39 kb) -- transcription of music roll note channels, processed with algorithm which increases volume in accordance with an estimation of the vacuum demand at any instant.

stibbons_AnimaticSunproc.mid (25 kb) -- transcription of music roll, including control tracks

stibbons_AnimaticSproc.mid (21 kb) -- transcription of music roll note channels, processed with algorithm which increases volume in accordance with an estimation of the vacuum demand at any instant.

stibbons_AnimaticS.jpg (328 kb) -- image of music roll presumed to be Animatic -S-

stibbons_AnimaticS.gif (24 kb) -- image file converted to GIF

15 January 2001