A-MSystems 1700 User manual

INSTRUCTION MANUAL
FOR
HIGH-GAIN DIFFERENTIAL
AMPLIFIER MODEL 1700
Serial #__________
Date____________
A-M Systems, Inc.
PO Box 850
Carlsborg, WA 98324
U.S.A.
360-683-8300 ♦800-426-1306 FAX:
360-683-3525
http://www.a-msystems.com
Version 11.0
March 2020

Contents
General Description........................................................................................................... 1
Operating Instructions....................................................................................................... 4
Theory of Operation........................................................................................................... 6
Specifications .................................................................................................................... 8
Warranty and Service ....................................................................................................... 10
Each Differential AC Amplifier is delivered complete with:
Four 3’ Cables
Rack Mount Hardware
NOTE
This instrument is not intended for clinical measurements using human
subjects. A-M Systems does not assume responsibility for injury or
damage due to the misuse of this instrument.

A-M Systems
131 Business Park Loop, P.O. Box 850 Carlsborg, WA 98324
1
Telephone: [phone] * 360-683-8300 * FAX: [phone]
E-mail: [email protected] * Website: http://www.a-msystems.com
General Description
Instrument Features
The Four-Channel Differential AC Amplifier Model 1700 is designed to amplify cellular
neurophysiological signals in applications requiring high gain, high input impedance,
low noise, high common-mode rejection, and powerline interference rejection. Typical
applications include: extracellular nerve recordings using suction or hook electrodes;
electromyographic (EMG) recordings from muscle using wire or needle electrodes;
EEG, ERG and EKG recordings. The instrument is not intended for clinical or
operating room measurements using humans.
The instrument consists of a high input impedance, low-noise differential input stage,
followed by high-frequency, low-frequency, and notch filters. The gain settings are
x100, x1000 or x10 000. It is also possible to connect a stimulator to each amplifier
channel and stimulate through the recording electrodes. The Model 1700 contains
four identical and independent amplifier channels in a single instrument, useful for
making extracellular recordings from several sources being monitored simultaneously.

A-M Systems 131 Business Park Loop, P.O. Box 850 Carlsborg, WA 98324
2
Telephone: 800
-
426
-
1306 * 360
-
683
-
8300 * FAX: 360
-
683
-
3525
E-mail: [e-mail] * Website: http://www.a-msystems.com
Controls and Connectors
INPUT: This 5-pin connector attaches the electrode cable
to the amplifier channel. The pin and electrode cable
wire designations can be found in the “Operating
Instructions” section in this manual.
STIMULUS: This 5-pin connector allows for external
signals to be applied to the electrode.
MODE (STIM-REC): This switch sets the channel to
Stimulus Mode or Record Mode. In Stimulus Mode,
the INPUT connector is connected to the signal from the STIMULUS connector and the
OUTPUT connector is disabled. In Record Mode, the INPUT connector is connected to
the amplification circuits and the signal is available at the OUTPUT connector.
GAIN: This rotary switch sets the amplifier gain to x100, x1000, or x10 000.
LOW CUT-OFF: This rotary switch selects the cut-off frequency of the Low Frequency
Filter for the amplifier channel. Signals below the cut-off frequency are reduced by a
factor of 100 (40 dB) per decade decrease in the input signal frequency. The Low
Frequency Filter may be used to reduce slow DC level variations in the signal being
recorded (See Bode plot page 3).
HIGH CUT-OFF: This rotary switch selects the cut-off frequency of the High Frequency
Filter for the amplifier channel. Signals above the cut-off frequency are reduced by a
factor of 100 (40dB) per decade increase in the input signal frequency.
NOTCH (IN-OUT): This switch allows the Notch Filter to be included (IN) in or excluded
(OUT) from the signal processing circuitry on a per channel basis. When radiation from
the power lines is present, it is picked up by recording electrodes creating unwanted
interference in the recording signal. This interference can be reduced through proper
grounding and shielding techniques. Occasionally it is impossible to reduce this
interference sufficiently to record relatively noise-free signals. The Notch Filter can
sufficiently reduce the interference. However, this filter causes some distortion in
signals below 100 Hz.
OUTPUT: This BNC connector provides the output signal from the amplifier channel.
POWER: This switch turns on power to all four amplifier channels.
GND: This connector is attached to the circuit ground for all four amplifier channels. To
obtain low-noise recordings, this terminal may be used to make a ground connection
to the recording medium.

A-M Systems 131 Business Park Loop, P.O. Box 850 Carlsborg, WA 98324
3
Telephone: 800
-
426
-
1306 *
360
-
683
-
8300 * FAX: 360
-
683
-
3525
E-mail: [e-mail] * Website: http://www.a-msystems.com

A-M Systems 131 Business Park Loop, P.O. Box 850 Carlsborg, WA 98324
4
Telephone: 800
-
426
-
1306 * 360
-
683
-
8300 * FAX: 360
-
683
-
3525
E-mail: [e-mail] * Website: http://www.a-msystems.com
Operating Instructions
General Notes
Any amplifier channel not currently in use should have its MODE switch in the STIM
position to protect the amplifier inputs. This grounds the inputs to the differential
amplifier circuitry.
Set the GAIN, LOW CUT-OFF filter, HIGH CUT-OFF filter, and NOTCH filter according to the
frequency content of the signal to be recorded.
While recording from biological preparations take care to keep all instrument cables as
far away as possible from the recording situation. This will assist in maintaining proper
grounding and shielding to insure a minimum of electrical interference.
Input cables are available to connect the amplifier to extracellular electrodes and/or
stimulators. These cables will attach to either the INPUT or the STIMULUS connector.
Additional cables can be ordered (catalog #692000, #701700). One end of each cable
is left open to allow for maximum flexibility. The pin assignments for the connectors
and the cables are as follows:
Pin Wire INPUT STIMULUS
A Black Signal + +
B White Signal - -
H Shield Driven Shield* Ground
D not used not used
E not used not used
NOTE: Pin H can be configured to be as a ground, rather than a driven shield. A
driven shield is used with the INPUT connector to minimize the effect of capacitance on
the cable, thus increasing common mode rejection. The shield is driven by a low
impedance source with a differential signal voltage from the amplifier. This driven
shield (the silver braid) should not be connected to ground, as this will cause
noise in the input signal. Instructions on how to convert pin H to a ground or shield
are detailed on the next page. Each channel can be configured independently.
The STIMULUS connector shield is connected to the system ground internally. Therefore,
any ground-referenced or isolated stimulator can be used with the STIMULUS connector.

A-M Systems 131 Business Park Loop, P.O. Box 850 Carlsborg, WA 98324
5
Telephone: 800
-
426
-
1306 * 360
-
683
-
8300 * FAX: 360
-
683
-
3525
E-mail: [e-mail] * Website: http://www.a-msystems.com
Configuring Pin H to be Shield or Ground
1) Determine if the channel is already configured as a ground or a driven shield. Using
a multimeter, set the meter to check for resistance. Measure between pin H and the front
panel ground connector. If the resistance is under 10 ohms, that channel’s pin H is set to
ground.
2) To convert the channel so that the braid is a ground, rather than a shield, remove
the cover, and look for two large capacitors on rear of the channel board. Near the
capacitors is a black jumper (J100). The jumper spans 2 of 3 pins on the connector on the
board. If the jumper is near the side marked GND, it is set to ground. If it is over to the
other side, it is a shield.

A-M Systems 131 Business Park Loop, P.O. Box 850 Carlsborg, WA 98324
6
Telephone: 800
-
426
-
1306 * 360
-
683
-
8300 * FAX: 360
-
683
-
3525
E-mail: [e-mail] * Website: http://www.a-msystems.com
Theory of Operation
Stimulus Mode
In Stimulus Mode, the INPUT connector is connected internally to the STIMULUS connector
to apply the stimulation signal to the electrode. All amplification circuits are grounded in
this mode, and the OUTPUT connector is disabled.
Record Mode
In Record Mode, the signal from the INPUT connector is coupled directly to the inputs of
a high impedance, low noise differential amplifier stage consisting of two operational
amplifiers with x10 gain. Direct coupling reduces the errors typically associated with
capacity input coupling. The operational amplifiers are in non-inverting mode and their
gain-setting networks connect through a common resistor to preserve high common-
mode rejection.
The common-mode voltage of the input signal at the inverting inputs of the operational
amplifiers is measured, and is used to drive the electrode cable shield. This improves
the common-mode rejection performance of the input amplifier stage. For this reason,
the driven shield should not be grounded.
The output signals are then connected to a second differential operational amplifier
circuit with a gain of x10. At this point, the differential electrode signal has been
amplified by x100 and converted to a single-ended signal with respect to ground. An
internal CMR potentiometer is trimmed at the factory to maximize the common-mode
rejection.
The signal passes through a double-pole low-pass filter, which attenuates frequencies
above the HIGH CUT-OFF switch setting. This stage provides no signal amplification.
If selected, the signal next passes through the Notch Filter. The Notch Filter is tuned
to the power line frequency and consists of a twin-T network in a feedback loop with an
operational amplifier. This stage does not amplify the signal.
The signal then passes through a double-pole high-pass filter, which attenuates
frequencies below the LOW CUT-OFF switch setting. Also included in this stage is
the final amplifier which provides x1, x10 or x100 gain to produce an output signal
according to the total gain specified by the GAIN switch.