I-AMP GPT 60-IV User Manual page 14

These output current levels are independent of the induction loop load impedance. The maximum
output level is internally limited to 4.5 AMPS Peak. This internal limiting is essential on a current
amplifier (or more correctly a transconductance amplifier giving a certain current output for a given
voltage input), such as the GPT 60-IV, preventing the highly dynamic input signal voltage levels from
exceeding the output current rating of the amplifier. This form of protection is not generally required
on more conventional voltage power amplifiers since limited power supply voltages prevent
overdrive (producing clipping distortion).
Note that the gain of the GPT 60-IV is set to provide full output of 4.5 AMPS Peak for a nominal
input of +4dBu (Balanced) (1.23 V RMS or 1.74V 0-pk or 3.47V pk-pk) when the input gain is set to
0dB. Full output is obtained with an input signal of -2dBu when input gain control is set to +6dB.
Note also that full output current is not required for all loop configurations. See, "Setting the Loop
Output Current" located on page 10. Saturation distortion in hearing aid pick-up coils and larger
external loop magnetic leakage can occur if magnetic field strengths greater than the Australian
Standard are generated.
6. Power On Switch: Turns mains power on to the GPT 60-IV
7. Mains Input Power:
cable (supplied). This connector also houses the main input power fuse. This fuse is a standard
M205 type, rated at 1 Amp.
8. Loop Output: The induction loop is connected to this 2-pin screw terminal connector. Note that the
loop output must be left floating with no output signal connecting to ground potential. Note also
that an induction loop load must be connected to the output of the GPT 60-IV for normal operation.
The output connections for the induction loop are:
Pin Number
The loop requires no minimum DC resistance and a maximum DC resistance of 1.8 Ohms to
enable full current output without overheating or high frequency clipping distortion.
The output terminals may be shorted at any time for testing purposes, even when the amplifier is
switched on.
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Mains input power is 240 VAC @ 50Hz via a standard IEC mains
Function
1 (+) Current Output
2 (-) Current Output
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