Having built and/or restored several mechanical musical instruments and pianos, I decided to build a mechanically played harpsichord from scratch. The harpsichord should be able to be played manually and also be able to play under computer control using a MIDI interface. This animation shows how the back of the key can be activated by a solenoid from below while still allowing the harpsichord to be played manually. Finally, the harpsichord should be able to remember the data downloaded from the computer and play music without being connected to the computer.
The starting point was the instruction book from a 1968 vintage Zuckerman Z-box harpsichord. These instruction books are still available from the Zuckerman Company in Stonington, Connecticut. I was also able to find some of the mechanical parts of a harpsichord on Ebay. Starting from a finished kit is also possible.
As I say, I started with the Zuckerman instructions, but proceeded to change them significantly. The first problem was the shape. All straight lines! I mean really - what kind of harpsichord has all straight lines? My first decision was to have a curved side. I began by cutting a base out of ½ inch birch plywood. The sides were made of ¾ inch birch plywood. The curved side was made up of three layers of 1/4 inch birch plywood that was kerfed as shown here. Kerfing is a woodworking technique whereby wood is made more flexible by a series of partial saw cuts. The following photo shows the three sheets of ¼ inch plywood of the curved side clamped up and being glued together. Also being clamped are two sheets of ¼ inch by 1-½ inch plywood which form a liner which helps support the soundboard and rests on the vertical side braces.
I began the keyboard construction with the keys and frame obtained from EBAY, however you might use a salvaged piano keyboard. The first step was to weight the keyboard so that the keys would return to the unpressed condition after pressing. Lead weights were used as shown in the following picture. A fishing store is a good source of lead weights. The keyboard building continued with the placing of felt and paper spacers on the keyboard pivot points as shown in the following picture. Part of the wood with the red felt in the picture would be later removed to allow the electromechanical actuators to depress the key by lifting the back of the key.
The soundboard was obtained from Zuckerman but could have been built from a large sheet of 1/8 inch spruce. Ribs were glued to the underside of the soundboard as shown here.
Once the bridge was shaped, it was attached to the soundboard using screws from the underside and ¾ inch wooden buttons as shown in the next photo. Notches were cut in the sides so that the ribs would not touch the sides. The next step was to fit up the soundboard and to fit up the pinblock, a massive 1-3/4 inch x 5-7/8 inch x 33-13/16 inch chunk of hard maple. EBAY is a good source of specialized hardwoods. The nut is shown on the pinblock. The next photo shows the jack rail with the pinblock removed.
The next photo shows the jackrail in place and the pinblock ready to be screwed and glued into the inner case. The soundboard has been removed to show the holes cut in the bottom of the frame, mainly to save weight. The completed jacks are assembled from a number of parts using these tools. Fifty-seven jacks. (notes) were completed for the final harpsitron.
The next photo shows from left to right: the pinblock glued and screwed in (wooden plugs cover the screw heads), the nut glued on the pinblock, the jackrail with some jacks, the soundboard and the bridge glued in and the hitchrail. The next photo shows the jack stop and the keyblocks which are made of mahogany.
The stringing begins with the bass strings. Each string requires a hitch pin at the far end of the photo , a bridge pin on the bridge and a nut pin on the nut and a tuning pin. The strings are placed according to my full size drawing.
The outer case is added by gluing and nailing to inner case. The outer case is ½ plywood capped with ¼ inch thick mahogany strips. The curved portion of the outer case is made up of two ¼ inch pieces of kerfed plywood. The nameboard and lockboard were cut from a ½ inch piece of mahogany. The next photo shows the curved side being clamped into position while the glue dries.
The lute stop lever is fabricated from a square brass rod with a hitchpin in the end. The lute stop lever imparts a sideways motion to the lute stop (mahogany in the picture) which will contain felt cushions which will touch the strings imparting a lute sound to the harpsichord.
With the veneer saw and mahogany veneer , the veneering of the outer case began. A maple inlay with some Carpathian elm burl was added for interest on the sides.
After the outer case was veneered the focus turned to the support stand. The stand serves two functions: 1. It supports the harpsichord. 2. It hides all the electronics which are below the harpsichord. Without the stand the harpsichord is just a regular harpsichord, with the stand it is an automatic, self-playing harpsichord. We begin the stand by obtaining ball and claw mahogany desk legs from Adams Wood Products. Some cleanup carving was done on each leg and mortises were cut for the sides of the tendons.
I will now discuss the electronics used in the project. The first item are the coils. Each coil consists of 200 feet of #30 magnet wire as shown in the following photo. The coils were wound using a coilwinder built from an electric screwdriver motor, electric footswitch and a variable DC power supply as shown below. Once the fifty coils were wound, it was time to construct the Actuator assembly as shown here. Two twenty-five parallel cables were used to connect the actuator assembly to the control boards. The completed actuator assembly is shown mounted on the stand with the harpsichord removed.
Two actuator drive boards were assembled. I designed these boards myself and each board has a microprocessor on it. One microprocessor is the master and decodes the MIDI serial stream from the MIDI source and stores the data on the onboard memory. It also drives the twenty-five solenoids controlled by this board. The LED bar has an LED for each note that lights when the note is played. The second board looks very similar but there is no onboard memory. It only decodes the MIDI data passed from the first board to drive the other 25 notes.
The next photo shows all the electronics in the harpsichord stand with the harpsichord removed. The solenoids activate the keys by pressing up on the back of the keys through a cutout in the bottom of the harpsichord case. A truly massive 7.2 amp, 24 volt DC linear power supply is used to drive the solenoids. This is the same view as the previous photo, but from the underside and the harpsichord has been placed on the stand. The keyboard in the background is the MIDI keyboard that I used for testing the HARPSITRON. This photo shows the harpsichord lifted slightly off the stand. You can see the actuator bar below and the bottom of the keys (red felt) above.
Once the electronics were checked out, it was time to do the finishing. Stain was applied to the veneered outer case. The music desk was mounted. Eventually the finishing was finished. The top was cut from ½ inch birch plywood, veneered with mahogany and finished. Hide glue was used in the veneering process. Of course the last step in any project is putting your name on it. Whew!!!
This page was developed for the hobbyest interested in building mechanical musical instruments. This site contains a general step-by-step instructions for building an electro-mechanical harpsichord and are meant as a starting point for the experimenter. Yes, of course there was a HARPSITRON I. Some specialized parts such as the microprocessor 'brain' and circuit boards are available for $20 and $60 USA at the email address below. The harpsitron is a MIDI acoustic instrument that requires modest electronics and woodworking skills.