I have finally finished the conversion of a small harpsichord to MIDI
operation.  Bob Lang previously reported on a MIDI operated harpsichord
which he has built.  I don't have anywhere near the skills of Bob in
woodworking or electronics so I used, wherever possible, ready-made
components.

The harpsichord is a small 51-note unit made in about 1960.  Instruments
built about this time are very much out of favour and can be purchased
fairly reasonably.  The MIDI control unit was purchased from John Wale
in England.  It's not expensive and it works wonderfully well.

I tested both Wurlitzer piano solenoids and Pianocorder solenoids and
I ended up using Pianomation solenoids from QRS.  The Pianomation
solenoids seemed to operate more silently than the others, so in spite
of the extra cost I decided to use them.  The other advantage is that
the Pianomation solenoids can operate at about 12 volts rather than at
about 100 volts.  It meant that I could use a standard power supply as
well as not risk electrocution.

The harpsichord is a fairly quiet beast so any thumping noise from the
solenoids could be intrusive.  I think the most difficult part of the
conversion was to design a system that would minimise the solenoid
actuation noise.

The solenoids were mounted on a wooden board located under the
harpsichord.  To reduce noise transmission each solenoid was attached
to the board with double-sided foam tape.

Perhaps the most novel feature of the conversion is the way in which
the solenoids actuate the keys.  To eliminate lost motion and to avoid
any possible noise caused by bouncing between the key tails and the
solenoids, the solenoid armatures (cores) were hung from the bottom of
the key tails using tiny O-shaped rare earth magnets.  Because the
travel of the solenoids and thus the keys is effectively self-limiting,
a key stop rail and a solenoid stop rail are not needed.  This
eliminated yet another potential source of noise.

I hope this may have been of some interest to the MMD group.  If anyone
has any MIDI files that might work well on a harpsichord, please email
them to me.

Phil Dayson