Version 2

(current version)

The electromagnets:
Magnetic Sensor Systems (solenoidcity.com)
E-77-82 Tubular Electromagnet
AWG 28 (5.3 ohms), infinite duty cycle
-Permanent magnets:
The Magnet Source
Ceramic Magnet Blocks
Part #07001

Rack and suspension system:
The rack is a 48″ long 2″ x 0.5″ T-slotted Extrusion (10 series, part # 2012) from 80/20 Inc.
A new suspension system was designed by the Instrumentation Lab at Miami University, allowing for much easier installation and adjustment. Specifically, this new system allows the size of the gap between electromagnet and piano strings to be adjusted much more rapidly and with greater precision. The suspension system consists of two brackets, one above the other, held in place by two metal sliders and springs. The electromagnet is suspended from the top bracket, and the bottom bracket is fixed to the rack. A knob connected to a threaded bolt controls the distance between the two brackets.
Some nice images can be found on the Instrumentation Lab’s page here.

Amplifier system:
The use of slightly larger electromagnets in Version 2 necessitated a more powerful amplification system. The new amp board was designed by Andrew McPherson, initially for his own similar system (see the Links section), and graciously shared for use in the EMPP. Many details about this system can be found in the following paper:
A. McPherson. Techniques and circuits for electromagnetic instrument actuation. Proc. New Interfaces for Musical Expression, Ann Arbor, MI, USA, 2012
PDF: http://www.eecs.umich.edu/nime2012/Proceedings/papers/117_Final_Manuscript.pdf
Design materials: http://c4dm.eecs.qmul.ac.uk/rdr/handle/123456789/25

The power source and casing for the new amplifier board were also designed by the Instrumentation Lab.

Audio interface:
The Echo Audio Audiofire 12 seems to be the only interface on the market with 12 analog outputs, perfect for this system!