A 3-D Helmholtz frame is used instead of the old cubic frame; the new frame sizes are about 6x6 feet. To reduce the phase difference and increase the precision of the measurement, the frame is made by three single turn Helmholtz coils.

An additional power amplifier is needed because of the new large frame. We have to provide more power to the Helmholtz frame to maintain a certain magnetic strength in the center of the 3-D frame. The original drive signals become the input signals of the new power amplifier. It is very hard to find a suitable

power amplifier, because the signal frequencies (80, 96, 120kHz) are out of any regular range. Finally, the Bryston's 6B SST model was selected. Although the input signals drives the amplifier to work far from its normal working frequency range(0-20kHz), it still can provide us undistorted powerful signals.

A new matching box is needed. The output signals of the power amplifier cannot be directly added to the the Helmholtz frame coils. The idea of a matching box is so wonderful, because it saves lots of power. The new matching box is constructed by a LC oscillating circuit, but it is different from the original parallel structure. The energy is alternatively stored between the Helmholtz coils and a special group of capacitors, so the input power just supplies the leaked energy and a very small consumed energy. Finally, the current in the Helmholtz coils is about 20~30 A, but the system provides about 50 Watts.

The system control, electronic projector control, data analysis and graphical display are under construction and programming.