Frequently Asked Questions

Settings and Adjustments

A: The DC offset can be adjusted using a rotary pot on the main board. Please contact technical support for a work instruction and please have the model number also.
A: The DC blocking can be set by creating what is essentially an RC high pass filter in the preamplifier stages. Please contact technical support for more detailed information and a work instruction.
A: Look on the back panel, for a rectangular black sticker. It should have a four-digit model number followed by an eight digit serial number.
A: The amplifier is separated from the equipment ground on the amplifier case. The case is supplied with a equipment ground, which is connected to the amplifier only through the 2.7-ohm resistor on the rear. Connection should be made either with isolated equipment (which have proper safety and equipment grounds), or extra care should be taken to ensure that all equipment grounds on all devices are at the same ground potential. Small differences may lead to undesirable currents, manifesting by heating or blowing the 2.7-ohm resistor.
A: The amplifier is essentially floating with respect to the enclosure. The amplifier and enclosure are tied together only at the point where the 2.7-ohm resistor connects. This stabilizes the amplifier and protects the connected equipment. It is strongly advised that the amplifier never be operated without this resistor being in place and in good working order.
A: The gain of the amplifier can be adjusted either in a fine adjustment of a few per cent, or the overall gain can be adjusted small to large values. For the 7224 the gain can also be fixed (bypassing the rotary control on the front). Please contact tech support for a work instruction.
A: There is a 3-pin (0.1” spacing) header at junction J5. A small thin solderless PCB protoboard can be soldered to the pins used for the custom compensation and resistors and capacitors can be repeatedly connected and detached from the PCB protoboard. An example is manufactured by BPS model BR1.
A: The amplifier employees a two-rail system with a bilevel switch that transitions from the lower rail voltage to the higher rail voltage as input and gain dictate (in the auto position). By locking the amplifier low, the amplifier is restricted from using the higher rail voltage (and limited to a lower voltage output), which increases efficiency and permits higher current. The high position eliminates the need to transition from the lower rail, improving signal tracking especially at higher output voltages and high frequencies.
A: In certain special circumstances it may be possible to replace the resistor with a jumper. Please contact technical support to discuss this if you believe it is necessary.
A: The amplifier is designed to operate within ±10% of nominal AC power voltage. All amplifiers should be provided with an equipment ground as part of the AC power supply.
A: Check the selector switch on the input card on the back of the amplifier. Normally it should be chosen to reflect the type of input used, but in some cases it may be necessary to use the differential switch setting when using the BNC connector in order to provide a ground lift.

Multiamp Operation

A: The inverting setting should be used only for series differential configurations. In this case only the follower amp should be set to invert.
A: When operating in a series configuration, all amplifiers require an optical isolation card (or “OPTOC”). Series and parallel configurations also require specialized communication cables (which are different for series and parallel), and other accessories. See section 1 of the Multiamp Configuration Guide.
A: In general each amplifier in a gang of series or parallel amplifiers each need their own settings. Consult the Multiamp Configuration Guide, or feel free to contact tech support.
A: When operating in series, single ended configuration it is very important that only the master amp have the 2.7-ohm resistor. The single ended series follower amplifiers should have the resistors removed and the connection between the common and chassis ground left open. For series differential and parallel configurations, the 2.7-ohm resistor should be in place for all amplifiers.
A: The 7224 series amplifiers should be operated in multi amp configurations in Controlled Voltage mode only. The 7548 and 7796 can be operated in parallel in controlled current, with only the master amplifier requiring compensation.

Faults and Warnings

A: The input commanded an output that the amplifier could not track. The output signal is generally seen as clipping. Normally the amp can be reset. However the amp can be set to go into standby upon overload. Note that the error signal is extremely sensitive (detecting errors as small as 0.05%) and the overload light may illuminate even when a satisfactory output is obtained.