Duo 773 Electrometer

Two-channel low-noise amplifier for intracellular microelectrode registration. Features capacitance compensation, signal filtering, current injection, overvoltage alarm, bridge balance, etc.

Overview
Specifications
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A Two-Channel Intracellular Amplifier for Comparative and Multiple Research

Two channels for intracellular or differential ISE
DC current generator integrated with external control input
Built-in low pass filter
Circuitry using a bridge to balance the electrode voltage
"Tickler" circuit
Each channel has built-in test ports.
Output offset controls and dual capacitance compensations
Includes two probe headstages, typically one high- and one low-impedance headstage.

Benefits

Single-ended, dual-channel recording
Differential recording
Electrode voltage drop is eliminated via a bridge circuit.
Either channel could be given a low pass filter.
The intracellular ISE can be employed with very high impedance channels.

Applications

Utilizing sharp micropipettes for intracellular electrophysiology
Intracellular recording in brain slices
Brain and spinal cord in vivo intracellular recording

The Duo773 includes built-in active filtering and distinct negative capacity controls that enable exact balancing of time constants for artifact-free differential measurement for intracellular dual or differential research. includes two probe headstages, 1015 and 1011 probes, for signal monitoring from KCl-filled electrodes as well as ion-specific microelectrodes.

Headstage for Proper Placement

Two tiny active probes with gold plating and epoxy seals can be placed right at the measuring location. The probes accept plug-in microelectrode holders with Ag/AgCl electrochemical half-cells. By covering the microelectrode holder at the probe's end with the driven guard shield that is included, stray capacitance can be decreased.

Compensation for Capacity

Both Channel A and Channel B have electrode shunt compensation capacities of up to 50 pF and 10 pF, respectively.

Circuit Tickler for Penetrating Cells

Cell penetration is aided by a tickler circuit. The oscillations' frequency and amplitude can be adjusted to account for variations in cell size or membrane thickness. The momentary switch, a foot switch, or the application of a signal to the remote tickler input can all be used to regulate the length of the tickle.

Active Filters

A -40 dB/decade active filter's low pass settings let you adjust the cutoff frequency from 1 to 30 kHz. Filtering can be applied to either probe outputs or bridge outputs.

Injection of Current

By sending a command signal to the stimulus input connection, Channel B can inject current through the microelectrode. The probe will produce a constant current copy of the input signal as its output. There are two available current delivery ranges: 50 nA and 500 nA, or an external source. This source can be utilized as a holding current for microiontophoresis as well as a means of supplying hyperpolarizing currents to stabilize the potential of the cell membrane.

Bridge Balance

Subtracts the extra electrode voltage caused by the recording micropipette's current delivery. Two ranges can be used to balance electrode resistances up to 1000 MΩ. The front panel output connectors x10 or x50 provide access to the balanced signal.

Independent Outputs

Each probe's output on the Duo773 is independent of gain filtering and balancing. The Duo773 also features a 10x and 50x output for simple interaction with the majority of data collecting programs.

Typical Setup

HEADSTAGE (PROBE)	712P (red, port B)	715P (blue, port A)
ACTIVE PROBE INPUT IMPEDANCE	>10¹¹ Ω	10¹⁵ Ω
GAIN	x1, x10	x1
OUTPUT RESISTANCE	100 Ω	100 Ω
OUTPUT VOLTAGE RANGE	±10 V	±10 V
MAXIMUM INPUT VOLTAGE	±15 V	±15 V
PROBE LEAKAGE CURRENT	5 X 10^-12 A	10^-14 A
DC POSITION ADJUST RANGE	± 300 mV	± 300 mV
ELECTRODE RESISTANCE TEST CURRENT	1 nA	1 pA, 1 nA selectable
INPUT CAPACITY COMPENSATION	+10 to -50 pF	0 to -10 pF
NOISE Input shorted 712P 20 MΩ carbon resistor	<50 µV p-p 10 kHz bandwidth <200 µV p-p 10 kHz bandwidth	<50 µV p-p 10 kHz bandwidth <200 µV p-p 10 kHz bandwidth
RISE TIME 10-90% direct input small signal 10-90% through 20 MΩ (-C "on")	1 µs, typical 25 µs, typical
CURRENT INJECTION (712P only)** Internal DC Current Externally commanded Current 712P (red, port B) External current command factor Current monitor Compliance Bridge balance Bridge amplifier gain	± 50 nA low range, ± 500 nA high range ± 500 nA low range, ±5 µA high range 20 mV/nA low range, 2 mV/nA high range 100mV/nA low range, 10mV/nA high range 3V low range, 10V high range 0-100 MΩ, 0-1000 MΩ x 10, x 50	n/a
LOW PASS FILTER	40 dB/decade, continuously variable 1-30 kHz
Fuse (Older models)	120 V: 0.5 A, fast, 0.25x1.25” USA 230 V: 0.25 A, fast, 0.25x1.25” USA
Fuse (2019 models)	120 V: 0.5 A, fast, 5 x 20 mm metric 230 V: 0.25 A, fast, 5 x 20 mm metric
METER SECTION Display Ranges Accuracy and resolution	3.5-digit LED 200 mV, 2000 mV, 20 V, 200 nA, 2000 nA 1 digit
DIMENSIONS: Instrument Probe	17 x 5.25 x 10 in. (43 x 13 x 25 cm) Diameter: 12 mm Length: 34mm
POWER	95-135 V or 220-240 V, 50/60 Hz
SHIPPING WEIGHT	15 lb. (7 kg)

* Despite the fact that injected currents are "constant," the system compliance of 10 V will always set a limit on the maximum current in a given circumstance.

** The 712P headstage can be used on either channel A or channel B, but when used on channel A, Current Injection requirements do not apply. On the B channel, the 715P headstage cannot be utilized.

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