IHF-1 INTERFACE AMPLIFIER
15 AC Input
17 +20V I/O
18 -20V I/O
Input connections. The IHF-1 interface amplifier has differential inputs for each channel. Balanced signals should be connected between the + and - inputs for each channel. Unbalanced inputs should be connected with the center or hot connection to the + amplifier input (1,8), and the shield connected to the - terminal (2,9). If there is no DC path between the chassis of the device to be interfaced and the IHF-1, a jumper may be necessary between the - amplifier input and the input common terminal (3,10). If there is a DC path already, performance may be enhanced by not jumpering the - input to common, as a ground loop condition may occasionally result.
Input impedance has been set at 24 kW for bridging or high-impedance inputs; if a loading input is required, pads are provided on the IHF-1 board to add a loading resistor at the positions marked R1 and R16.
Output connections. The IHF-1 amplifier uses a precision cross-coupled differential output circuit. To drive a balanced device, just connect the + (5,12) and - (6,13) outputs of the IHF-1 to the + and - inputs of the device to be driven. A shield may optionally be connected to the IHF-1 common terminal. If driving an unbalanced device, connect the + output of the IHF-1 to the device input, and the - output of the IHF-1 to the device ground. If you need to reverse phase, reverse the IHF-1 connections. But the IHF-1 output pins must not be left floating or output level instability may result (just as would be necessary with a transformer-balanced output stage).
Power supply connections. The IHF-1 amplifier is designed to connect to a variety of power supply types that may be encountered. If the amplifier is being located inside a piece of consumer equipment, it is highly likely that +/- power supply voltages are available there as well. Since the IHF-1 contains its own onboard filtering and regulating circuits, connection may be as simple measuring the voltage present at the output of the equipment’s rectifier bridge, and connecting there. The only caution is that input voltages should be at least +/- 20 volts (so that the onboard +/- 18-volt regulators can work; they must drop at least 2 volts to provide regulation), but no more than +/- 35 volts (the maximum rating of the voltage regulators). When connecting to a split supply, use the +20V I/O, -20V I/O, and power supply COMmon terminals. Alternatively, if an AC supply voltage of 15 VAC to 25 VAC is available, this may be used to power the IHF-1. Connect the power supply leads to AC IN and power suppy COMmon terminals.
If the amplifier is being mounted externally, it may be desirable to provide an external power supply. Dav Tronics provides, as an option, a CSA/UL approved AC adapter that is rated 16 VAC out at 300 mA. This can power up to six IHF-1 assemblies. Or you can provide your own AC or bipolar power supply. It’s flexible!
Gain setting. Each amplifier has a four-position gain-setting strap. This strap determines the maximum gain of the amplifier, which is nominally 0 dB, 6 dB, 20 dB or 40 dB. The trimmer potentiometers determine the exact gain setting. Turning the trimmer maximum clockwise will result in the nominal maximum gain for the strap position. Gain can be reduced from this amount by turning the trimmer counterclockwise.