A-MSystems 3000 User manual

INSTRUCTION MANUAL
FOR
AC/DC DIFFERENTIAL AMPLIFIER
MODEL 3000
Serial #__________
Date____________
A-M Systems
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 7.0
March 2020

Contents
General Description............................................................................................................................ 1
Instrument Features........................................................................................................................... 1
Controls and Connectors ................................................................................................................... 1
Configuring the Model 3000 for use with a head stage................................................................... 5
Operating Instructions....................................................................................................................... 6
Typical Set-Up Procedure.................................................................................................................. 6
Theory of Operation........................................................................................................................... 9
Specifications..................................................................................................................................... 11
Warranty and Service ...................................................................................................................... 13
Each AC/DC Differential Amplifier is delivered complete with:
One 3 Foot Cable
Remote Power Supply
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.

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General Description
Instrument Features
The AC/DC Differential Amplifier, Model 3000 is a single-channel, differential amplifier
that can be used with or without a head stage probe. The instrument is designed for
low-noise recordings from excitable tissue. It is intended for extracellular recording
and/or stimulating in conjunction with microelectrodes. It can be used in a number of
research or teaching applications requiring extracellular neurophysiological recording
from excitable tissue, such as nerve, muscle (EMG), EEG, EKG, and ERG recordings.
The instrument is not intended for clinical measurements using humans.
The Model 3000 contains a high-gain, low-noise differential amplifier stage followed by
low frequency, high-frequency, and notch filters. Three operating modes are available
to accommodate recording, stimulating, and verification of electrode impedance.
Record Mode offers six levels of signal gain (x50, x100, x500, x1000, x5000, and
x10,000). Stimulus Mode allows the current passing through the electrode to be
measured during stimulation at six levels of gain (5V/mA, 10V/mA, 0.05V/µA, 0.1V/
µA, 0.5V/µA, 1V/µA). Impedance Mode utilizes an internally calibrated current source
to allow in situ verification of electrode impedance and adjustment of capacitance
compensation. Units that are sold with a head stage are pre-configured to work with
the headstage, and the front panel gain values include the gain of the headstage.
Controls and Connectors
Input Controls
PROBE: This 15-pin connector receives a signal either directly from the electrodes (non
head stage version) or from the Head Stage probe for further processing.
INPUT SELECT (DIFF-MONO-GND) (non headstage version only): This switch sets the
input for differential operation, monopolar operation, or grounds the inputs to the
amplifier.
INPUT LEADS (standard): Supplied with the Model 3000 is a DB-15 connector with three
leads. The black wire is the “+” electrode lead. The white wire is the “-” reference
lead. The silver wire is a driven shield, and should not be grounded! This wire
serves to minimize signal loss due to capacitance.
HEADSTAGE PROBE (optional): The Headstage Probe has three sockets for connection
to electrodes. PROBE+ is used to connect to the electrode (usually a high impedance
recording microelectrode; It is the larger 2mm jack). PROBE- is used to connect to the
indifferent lead. Either the PROBE GND connector, or the front panel GND must be

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connected for proper operation. Usually the PROBE GND connector is tied to the
indifferent lead. If you desire to have the current constrained to a known path you may
want to place the GND elsewhere. Actual GND placement depends on the application.
Mode Controls
ELECTRODE TEST: This toggle switch activates (ΩTEST) a 2 nA p-p, 100 Hz
squarewave current source used to test electrode resistance and to adjust the
capacitance compensation. The ELECT TEST switch must be set to ΩTEST and the
STIM-GATEREC switch must be set toREC for the test signal to be monitored. (Note:
Recording and reference electrodes should be in a saline solution for resistance
testing.) To accurately measure the impedance, verify at the OUTPUT connector that
the signal is a square wave of 100 Hz, adjust the CAPACITY COMPENSATION knob to
square the corners of the waveform. The amplitude of the square wave is a direct
measure of impedance in each of the six ranges (0.1Vp-p/MΩ, 0.2Vp-p/MΩ, 1Vp-
p/MΩ, 2Vp-p/MΩ, 10Vp-p/MΩ, 20Vp-p/MΩ).
STIMULUS: This isolated BNC connector enables a stimulus source to be utilized to
pass current through the electrode while the unit is in stimulate mode (STIM). The
center pin of the BNC is the + input and the outer conductor is the - stimulus input.
When the unit is in the (STIM) mode the output will be a measure of the current
passing through the electrode in six ranges (5V/mA, 10V/mA, 50mV/µA, 0.1V/µA,
0.2V/ µA, or 1V/µA).
STIM-GATE-REC: This toggle switch controls the operating mode for the Model 3000.
The switches allows the user to select Record Mode (REC) Stimulate Mode (STIM), or
Gate Mode (GATE).
Output
Output: This BNC connector provides the output signal from the amplifier.
GND: This connector on the front panel provides access to the circuit ground. Either
the PROBE GND connector or the front panel GND must be connected for proper
operation. Usually the PROBE GND connector is tied to the indifferent lead. If you
desire to have the current constrained to a known path you may want to place the
GND elsewhere. Actual GND placement depends on the application. For low-noise
recordings a ground connection should be made in the recording medium (i.e. bath
ground, animal ground, etc.).
GAIN: This rotary switch controls the level of signal gain for its channel while the
channel is in Record, Stimulate, and Impedance Mode. In Record mode (REC) the
switch allows the user to select from X50, X100, X500, X1000, X5000, or X10,000 gain. In
Stimulate mode (STIM) the gain switch selects one six ranges (5V/mA, 10V/mA, 50mV/
µA, 0.1V/µA, 0.2V/µA, or 1V/µA). In Impedance test mode (REC, ΩTEST) the gain

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switch selects one of six ranges (0.1Vp-p/MW, 0.2Vp-p/MΩ, 1Vp-p/MΩ, 2Vp-p/MΩ,
10Vp-p/MΩ, or 20Vp-p/MΩ).
Capacity Compensation
Capacity Comp: This knob is used to adjust an active feedback circuit to compensate
for up to 30 pF of electrode capacitance. The capacitance compensation can be
adjusted with the electrode in the experimental preparation using the internal
squarewave generator and an oscilloscope connected to the output BNC. This
control should be adjusted to obtain the sharpest corners possible on the square-wave
with very little overshoot. Clockwise rotation of this control increases the capacity
compensation. Warning: Turning the Capacity Compensation too high will cause the
circuit to oscillate wildly and change frequency, and may also cause the electrode to
behave in a similar manner. The extreme swings in voltage may be harmful to neural
tissue, and care should be exercised in using this control. It is a good practice to turn
the knob half way off once the impedance is measured, to minimize the chance of
overcompensation when recording.
DC Offset
DC OFFSET KNOBS: These two knobs sets the variable DC offset voltage, which is
summed with the input voltage. This feature may be used to compensate for electrode
potentials and to position the signal trace on an oscilloscope recording device. An
input offset range of 0.0 V to ±250 mV is available. The COARSE knob will cover 250
mV and the FINE knob will add up to 25 mV to the COARSE knob’s position.
DC OFFSET SWITCH (+ OFF -): This switch sets the DC offset polarity or alternately turns
the feature OFF.
OVER RANGE INDICATORS: These LED’s will illuminate when the output of the device is
beyond its limit of +10 V (top LED) or -10 V (bottom LED).
Filter
HIGH PASS: This rotary switch enables the user to select the lower boundary frequency
at which point the channel’s input signal begins to be cutoff. Signals below the cutoff
frequency will be attenuated by a factor of 100 (-40 dB) per decade decrease in the
input signal frequency. For example, if the HIGH PASS switch is set at 100 HZ, then a 10
Hz signal will be attenuated by a factor of 100 while a 1 Hz signal will be attenuated by
a factor of 10,000. The high pass frequency should be selected based on the
frequency content of the signal to be recorded. One of the uses of this filter is to
reduce slow variations or DC levels in the input signal. When the switch is in the DC
position the high pass filter is off.
NOTCH: This switch allows the Notch Filter (-50dB at 60Hz) to be included in the signal
processing path (ON) or bypassed (OFF). Warning: Although the Notch Filter provided

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can significantly reduce unwanted interference from the power source, it will cause
some distortion of the signal, especially in frequencies below 100 Hz. Therefore, the
Notch Filter should only be used if other noise reduction techniques such as proper
grounding and shielding are inadequate.
LOW PASS: This rotary switch enables the user to select the upper boundary frequency
that the input signal begins to be cutoff. Signals above the cutoff frequency will be
attenuated by a factor of 100 (-40 dB) per decade increase in the input signal
frequency. For example, if the LOW PASS switch is set at 1 kHz, then a 10 kHz signal
will be attenuated by a factor of 100 while a 100 kHz signal will be attenuated by a
factor of 10,000. One of the uses of this filter is to reduce high-frequency noise that is
above the frequency content of the signal being recorded.
Head stage indicator
HEAD STAGE: This LED indicates whether the unit is configured for use with (HEAD
STAGE lit) or without (HEAD STAGE off) a head stage (See configuring the Model 3000
for use with a head stage pg. 5).
Power Supply
POWER:This toggle switch is the main power switch, controlling the DC power input to
the main circuit of the instrument. The LED next to the toggle switch is lit when the
instrument is ON. This button does not control the power input to the remote AC
Power Supply. Once the remote AC Power Supply is plugged in there is 30 Volts DC
to the unit. If this situation is undesirable please unplug the remote AC Power Supply
when the instrument is not in use.

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Configuring the Model 3000 for use with a head stage
If your unit was sold with a head stage then the jumpers are already set to the head
stage position, however if you purchased the head stages at a different time than the
model 3000 you will need to complete the following procedure.
To set the model 3000 for use with a head stage, all jumpers must be set to the H
position (see figure 2 below). Once the jumpers are in the H position the unit can only
be used with a head stage. To return the unit for use without a head stage simple
move the jumpers to their previous position.
Calibrate the unit for headstage. Set the unit in the following positions:
HIGH PASS: DC NOTCH: OFF CAPACITY COMP: Counter Clock-wise
DC OFFSET: OFF ΩTEST: OFF MODE: REC
Ground the head stage inputs and adjust R41 for zero volts at the OUTPUT.

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Operating Instructions
Typical Set-Up Procedure
The Model 3000 comes with an input cable that connects to the DB15 input. One end of
this cable is left open to allow for maximum flexibility in connecting to extracellular
electrodes. The Model 3000 will function properly in this configuration if the head stage
(HEAD STAGE) LED is off.
The Head Stage Probe (optional) connects to the DB15 input and will function properly
if the head stage (HEAD STAGE) LED is on. The probe is used to connect the
extracellular electrodes to the amplifier. The GND connector on the front panel of the
amplifier should be used as the system ground in the particular recording medium (e.g.
bath or animal ground). Note: Either the Head Stage PROBE GND or the GND on the
front panel must be connected to provide a return current path. If neither ground is
connected the Head Stage Amplifier will saturate and no signal will be measured.
Care should be taken to keep the power cables from all instruments as far away as
possible from the recording setup. One exception is the DC power cable that supplies
power to the model 3000. This side of the cable is DC and therefore does not carry
disrupting power line frequencies. Proper grounding and shielding techniques
should be used to insure a minimum of interference.
Recording
This is a generalized procedure for setting up the AC/DC Differential Amplifier for
recording. Portions of this procedure may need to be modified for your specific
application.
1. If you are planning on using the Model 3000 with a head stage connect the Head
stage Probe cable to the PROBE connector.
2. Set the instrument controls as follows:
HIGH PASS DC
NOTCH FILTER OFF
LOW PASS 20 kHz
CAPACITY COMP. counterclockwise
DC OFFSET FINE AND COARSE knob counterclockwise
DC OFFSET (+ OFF -) OFF
GAIN knob 50
INPUT (DIFF MONO GND) GND

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MODE (STIM-GATE-REC) REC
ΩTEST OFF
3. Turn on power to the Model 3000 and allow it to warm up for 5 minutes.
4. Non Headstage option: connect measuring electrode to the black wire and a
reference electrode to the white wire of the probe cable.
Headstage option: connect measuring electrode to the +
input of the head stage and a reference electrode to the -
input of the head stage (see diagram to the right). Note: the
reference electrode can be tied to the gnd input on the head
stage. Clamp the Head stage in amicromanipulator.
5. Dip the measuring and reference electrode into a beaker of
physiological saline solution (or the solution in which the
tissue will be bathed). The solution should have the same
temperature and ionic strength as that in which
measurements will be made. Note: immerse the measuring electrode to
approximately the same depth as will be used during the measurement.
6. Connect an oscilloscope to the OUTPUT BNC, with the horizontal sweep rate set to
2ms/division. Zero the scope. Flip the input switch to DIFF.
7. Observe the offset potential between the two electrodes on the oscilloscope. Set
the DC OFFSET (+ OFF -) switch to the appropriate polarity and adjust the DC OFFSET
knob to zero the amplifier output. Note: make sure your oscilloscope is in DC
mode.
8. Turn on the ΩTEST button to inject a 100 Hz square-wave current through the
electrode.
9. Adjust the oscilloscope for a good display of the square-wave. The Oscilloscope
will display a square wave at 0.1 V peak to peak for every 1 MΩof electrode
resistance.
10. Increase the CAPACITY COMPENSATION to “square-up” the corners of the waveform.
Avoid overcompensation, which will cause ringing, excessive noise, and high
frequency oscillation.
11. Turn the CAPACITY COMPENSATION knob to approximately half way between its
present position and the off position. This will minimize the chance of
overcompensation during recording.
12. Turn off the ΩTEST switch to stop the test signal.
13. Apply the electrodes to the experimental preparations.
14. Apply the HIGH PASS, LOW PASS,and NOTCH FILTERS if necessary.
15. Increase the gain switch until the output voltage is in the range necessary for
saving data. Note: The GAIN Switch should be set so that the signal at the OUTPUT