Automatic Musical Company
Expression Controls

(Photograph courtesy of Terry Barnes)

Soft pedal (hammer rail) control valve box in Automatic Musical Company's Mandolin Piano #27096. This small control unit is inconspicuously fastened to the inner right side of the piano case and is located between the case and the piano action with little room to spare. It is held in place by the single L-shaped bracket visible at the front of the unit. All tubing is missing in this photograph, but the hole in the top of the unit for the rubber tubing connection to the soft pedal pneumatic is visible.

(Photograph courtesy of Terry Barnes)

Bottom end view of the soft pedal control unit in Automatic Mandolin Piano #27096. This view shows three of the tubing connections. The large hole (with a remnant of old broken off rubber tubing still in place) connects to a vacuum source. The smaller bottom hole (near the edge) connects to tracker bar hole #1 (soft pedal on). The other tubing connection on the little wood block that juts out from the side goes to tracker bar hole #2 (soft pedal quick release).

(Photograph courtesy of Terry Barnes)

Side view of the soft pedal control box in Automatic Mandolin Piano #27096, and showing the atmospheric vent port for the soft pedal quick release. The little block of wood at picture bottom is the connection for tracker bar hole #2 (soft pedal quick release).

(Drawing courtesy of Terry Barnes; Text labels by Terry Hathaway)

This drawing, courtesy of Terry Barnes, is a side cutaway view of the soft pedal control unit. The vacuum supply is connected at left, reducing the air pressure in the left side valve chamber. When tracker bar hole #1 is uncovered by the music roll the pouch in the left side valve chamber inflates, thereby opening the pallet valve. This admits vacuum to the right side valve chamber, which is also connected to the hammer rail lift pneumatic .If the perforation for tracker bar hole #1 is extended the soft pedal remains full soft, but whenever the perforation passes over the tracker bar the left side soft pedal valve closes, allowing a gradual release by means of a screw adjustable bleed situated in the rubber tubing between the control box and the soft pedal pneumatic. However, once tracker bar hole #1 is closed and if tracker bar hole #2 is opened, there still being residual vacuum in the right side valve chamber, the pouch for the quick release valve will inflate and open the pallet valve so as to quickly vent the chamber to atmospheric pressure, causing the soft pedal pneumatic to quick release.

(Photograph courtesy of Terry Barnes)

The three distinct layers making up the soft pedal control box in Automatic Mandolin Piano #27096. At the left is the bottom or pouch board. In the center of each elliptical shaped inflatable pouch is a piece of wood with rounded edges and with a small wooden dowel glued in its center. The dowel is what pushes up on and opens the pallet valve situated immediately above it. In the center is a bottom view of the board that holds the pallet valves, with the side shown being the one that mates with the pouch board. At right is a bottom view of the thin wood top cover for the center of the sandwich, the valve board.

(Photograph courtesy of Terry Barnes)

The pouch and valve board sections of the soft pedal control box in Automatic Mandolin Piano #27096. At left is the pouch board as described in the above pane, but here the individual bleeds are clearly visible, they appearing as small holes below the pouch and slightly to the left of the wood pressure pads in the center of each pouch. At picture right is a top view of the valve board, fitted with two pallet valves. Each valve is faced with leather, which extends beyond the backside of the valve where it is both glued and tacked in place to form a very flexible hinge. The center tack also holds a spring that rides in the groove cut down the back center of the valve block, and that keeps the valve firmly closed unless the spring tension is overridden by the inflated pouch underlying the hinged pallet valve.

(Photograph courtesy of Terry Barnes)

Adjustable in-line soft pedal bleed block in Automatic Mandolin Piano #27096. The bleed block is inserted into the rubber tubing connection from the soft pedal control box and the soft pedal (hammer rail) lift pneumatic. By means of the adjustable screw the amount of air bleeding back into the system can be precisely controlled, so that when the soft pedal valve closes (and the quick release function is not used) the hammer lift pneumatic can gradually fill with air and release, thereby providing a moderate crescendo effect.

(Photograph courtesy of Terry Barnes)

Sustaining pedal control box and combined actuating pneumatic in Automatic Mandolin Piano #27096. The "rocking arm" on the top of the pneumatic is for finely adjusting the travel of the pneumatic to the soft pedal lift rod that is connected to the actual foot operated soft pedal at the front bottom of the piano. The large brass nipple sticking up on the right side of the unit goes to a vacuum supply. The small nipple sticking out of the end (with a rubber tube attached) goes to the tracker bar.

(Photograph courtesy of Terry Barnes)

Rear side of the sustaining pedal control box and combined actuating pneumatic in Automatic Mandolin Piano #27096. The atmospheric vent port visible in the upper side is for the internal sustaining pedal valve.

(Photograph courtesy of Terry Barnes)

View of the internal sustaining pedal rocking-lever type valve mechanism in Automatic Mandolin Piano #27096. This valve system is reminiscent of smaller but nearly identically designed  unit valves found in some Automatic Musical Company stacks. At far left is a red fiber disk with a tiny bleed hole. A little to the right is the circular pouch with a wood pressure pad that is glued to a riser forming one end of a rocking lever that pivots on a center bushing. At right is the valve itself, which normally rests in the closed position (this picture shows the valve upside down). When a vacuum is applied to the chamber it also tends to pull the valve closed. The button valve itself is enclosed in an extruded metal pan, which (with the valve inside) is carefully aligned and tacked in place, and then sealed around its base and the two tack holes.