In the March/April '96 Amica Bulletin, an article appeared
purporting to compare the Ampico B with previous versions. Some
interesting observations were reported in this article which take
exception to some of the very things mentioned in its developers'
diary, its head of the Ampico Roll Arranging department of the day,
bench measurements that anyone can make, and any good high school
physics teacher.

   I thought it was strange that Amica's technical committee didn't
catch at least a few of these errors, but perhaps, upon learning of
them, they will consider rereading the article and perhaps correcting
it for archival value, at least.

   Authors writing about these instruments have (in my opinion) a
responsibility to everyone to check their facts, and frankly, that is
exactly what the technical committee should have done and didn't do,
apparently because they didn't know enough themselves to object. It's
understandable that sometimes an article slips through with a few
mistakes, and since nobody is perfect, we all understand that. If the
author finds it, it is his obligation to correct himself in a future
issue. If he doesn't wish to do so, it then should become the editor's
obligation to correct the mistake. But in this particular article, we
have so many glaring errors that it might be wondered if the author
really understands the Ampico expression system at all.

   In the next several issues of AMD, I will try to post one or two of
the exceptions taken with the article, and also invite comments. After
all, we are all human and prone to making mistakes, so we all know how
it feels. Some of the errors I see are in the lack of thoroughness of
the statement, which, in my opinion, makes it just as wrong as if it
were technically incorrect, because it insinuates a wrong conclusion.

   You may not see it that way, or you may see what he is getting at,
and that's what makes for good dialog-- as long as we can keep it
technical and objective. I refuse to get down in the dirt for a fun
subject like this. So let's keep it light, if you don't mind, and not
take it too seriously. Here goes:

1. (In attempting to discredit the Ampico model B, fo which he said in
   a former article, "The Model B skips notes", Jeffrey Morgan totally
   discredits his own understanding of the reproducer in this one
   statement) See  p 71, Para 3. "Furthermore, the Model B crescendo
   system does not initiate corrective action for stack transients as
   do most earlier Ampico crescendo systems."

ANS: That couldn't be more wrong! If he doesn't understand the basics
of ALL Ampicos, and the reason that the number of notes played are
never compensated for on the roll (as in Duo-Art coding) then Jeffrey
hasn't done enough homework to be writing articles.

   The regulating pouch (or curtain) is a lightweight airtight
pneumatic cloth which is placed between the "control" vacuum and each
half of the stack. On the stack side of the curtain are two devices,
the stack and the supply, which are separated by a grille (grid) having
a blank space (no holes) in-between.  Normally, without any control
vacuum under the curtain, the supply would suck the curtain tight
against its grid (a perforated piece of celluloid) and that half of the
stack would then be cut off. But there is always a fixed "bias" vacuum
called "first intensity"  which keeps just enough curtain peeled back
to play any or all notes called for at that intensity.

   No matter what the demand or "stack transient" due to the number of
notes being played, the curtain allows just enough flow to balance the
control vacuum under it exactly without momentum or overshoot.

   Let's suppose the stack is almost starved (except for the fixed leak
which provides a tiny flow of air at all times) and one note is played
down. That one note creates a tiny extra demand-- a very small
percentage of the capacity of the supply, but is nevertheless sensed by
the pouch because of a bit of air tension as the note valve begins to
actuate. Air "blows" the regulator down just a very tiny bit-- IN
PROPORTION TO the demand, and instantly the supply is uncovered to
exactly the same degree because of a constant "weight" on the curtain
by the control vacuum which has been set to a certain amount
previously. Where will the curtain balance at now? It will try to come
to rest at a place in which it can exactly balance the pressure below
with the pressure above.

   Does it make any difference now when two huge chords are suddenly
played down at the 1st intensity? None whatever. The device simply
balances by peeling itself away from the supply to the degree that the
pressure above the curtain equals the pressure below. And the nice part
about this is that there is no built-in error, like having a separate
disk regulator valve in line but separate from the control device that
is itself also affected by the stack flow but is not compensated for
that.

   Now by adding other inputs under the regulating pouch, one is able
to change the balance point instantly, according to the roll coding,
and have a dynamic performance which is faster than the requirements of
the music.

   The model B "makes its living" compensating almost perfectly for
every change in stack pressure, including changes that no other piano
can even begin to sense. It is the perfect regulator if there ever was
one. So while stack transients (quick changes in pressure due to played
notes) is still a problem for every other reproducer ever built, the
Model B can totally ignore them because it is actually faster than the
valves themselves.

   It is incomprehensible that Jeffrey Morgan presumes to teach others
that a proportional curtain (or "C" pouch as he calls it) doesn't
compensate, and doubly incomprehensible that no one caught this
absolutely obvious mistake, since it blows half of his article right
out of the water along with it. The next installment will start sinking
the other half of his "Observations" into obscurity. You will
understand why I say that this article is raving and unsound.


2. p 70, para 2; "Ampico's highly stabilized expression system combined
   with its spring loaded stack equalizer pneumatics make the task of
   keeping up with normal stack operating demands (especially at soft
   playing levels) much less dependent upon expression coding."

ANS: The spring loaded equalizers ( I call winkers) task is not to
provide help in keeping up with stack demands. In fact, they actually
add a little bit to the demand requirements. They act as eveners or
capacitors which are there as a compromise between a little bit less
expression capability at low expression levels, and the remote
possibility of the regulator valve to overshoot, shutting off vacuum
from the stack for a split second. As it turns out, they were really
not needed, but historically, we should rebuild and replace them
exactly as they were made.

   The worry that the regulator valve could clamp the stack supply for
a split second and miss a note or two caused Ampico to provide these
equalizers that store a little energy in their springs and release it
when the tension gets too low, creating just enough vacuum at the stack
nipple to oppose the valve closing all the way. They are a "fix" for a
possible problem with the regulator valve _at the expense of demand
requirements_!

   I have also played some sensitive Ampico rolls both with and without
the equalizers and prefer it without. Some say they don't hear any
difference at all (which doesn't surprise anyone, either ).

   The objection I have to the statement is very simply this: Stack
demands, caused by notes, chords, and expression from the roll, are
compensated in the model A strictly and entirely by feedback from the
regulator output to the three intensity pneumatics. Read the
Inspector's Manual. Equalizers do not even figure into this, but rather
increase, overall, stack demand slightly by storing a part of the
energy in their springs, the rest being normal leakage which any
pneumatic will have a bit of.

   The next exception is a humorous one:

3. p 70, para 3. "Moreover, the rather cumbersome mechanical linkage
   shown in this extremely ingenious design may well have impeded its
   agility (...fig 8)."

ANS: He speaks of this device prior to this quote as having never seen
production.  My question is, "What is 'an extremely ingenious,
cumbersome design'?-- That was never used in a piano?" Perhaps I was
humming the wrong mantra when I read that one, but I don't think
anything would have helped much. We used to call them Rube Goldbergs,
Jeffrey. Something overly complicated and slow for what it had to do.
Ingenuity to me represents the simplest solution to a problem, not the
most expensive, difficult, cumbersome, and almost impossible to adjust
solution to the problem.

4. p 70, para 1. "During those periods when the crescendo driver is not
   engaged by an external signal (he is referring to the Ampico
   Crescendo mechanism, but uses his own terms), the action of the
   pallet applies inverted feedback from the stack to driver control,
   thereby continuously tailoring the strength of the spring pneumatic
   to the action of the main regulator valve."

ANS: Does anybody understand that? Why not just say that during periods
of crescendo activity the Crescendos maintain equilibrium with their
spring tension at the first intensity level by bumping a pallet valve.
Does anybody notice something else here as well? Jeffrey says that this
"inverted feedback" comes from the stack to the Crescendo. Could anyone
simply look at a schematic and inform me via e-mail what he is talking
about?

   The set point, which Ampico calls the "First Intensity," isn't
really inverted feedback in one sense anyway when you look at the
entire system, although I will accept it on the grounds that it
reverses itself. Feedback, though, is a controlling sample (of  output)
which usually is returned from the output of a system, back to the
input, or at least across two stages or more elements of a system. It
is bad terminology here. It would be better called a set point
controller.

   The supply to the Crescendos comes directly from the pump. There are
three other tubes. One is its output to the spring pneumatic, and the
other two control slow and fast crescendo/decrescendo and go the the
trackerbar. So with that in mind, how does Jeffrey justify saying that
any inverted feedback comes to it from the stack? Just curious, since
it must be totally isolated from the stack in order to do its job and
oppose the three intensity pneumatics whose supply happens to be the
stack vacuum.

Craig B.