"A superb low noise preamplifier"

The heart of the 2400A system is its versatile preamplifier section made up of high gain, low noise neutralized preamplifier, active filters, and an audio amplifier. The neutralized input capacitance allows fast rise time signals to be viewed with high microelectrode resistance's. 

Since extracellular and micro-iontophoretic recording can involve microelectrode resistance's into the tens of megohms, current noise (in addition to voltage noise) becomes an important consideration. The 2400A system preamplifier was designed to be used with both high and low impedance electrodes. In all situations it will provide noise levels close to the Johnson noise theoretical minimum (produced by the microelectrode resistance). 

The voltage gain of the preamplifier section is very high (switch selection of: 50, 100, 200, 500, 1000, 2000, 5000, or 10,000). No other additional amplification should ever be needed between the microelectrode and the recording instrumentation. 

A CALIBRATE switch allows a precise signal to be passed form the preamplifier to calibrate recording or viewing instrumentation 

A full complement of active filters means that frequency response can be tailored to provide maximum signal to noise ratio. The seven frequencies for both the high and low frequency cutoff filters were chose to provide for a complete range of recording bandwidths. Selection is made by convenient, fast action, push button switches. 

By switching on the twin-tee active LINE NOTCH FILTER, interference problems caused by 60 (or 50) hertz power lines are eliminated. 

The internal audio power amplifier fulfills the requirement for audio monitoring of the preamplifier output. The audio level is determined by the MONITOR control and a separate 8 ohm speaker (available as an option) plugs into the instrument back panel to provide sound where you want it. 

CELL STAIN

Your microelectrode recording site can be marked for easy visual identification by using either the STAIN switch or the controlled but smaller currents from the CURRENT PUMP. 

The STAIN generator provides a high level resistive limited current with polarity selections for use with both metal and glass electrodes. The 2400A also provides for any future stain requirements vow may have by giving you direct access to the electrode via the EXTERNAL BNC connector. 

An ultra low noise experimental setup the absence of capacitive loading effects are made possible by the use of a probe headstage containing the first preamplifier gain block and also all circuitry needed for the other microelectrode termination's. 

Capacitive neutralization is at your fingertips with a high resolution neutralization control located on the probe. This feature gives you the capability to fine tune signal rise times when your miroelectrode resistance's are greater than a few megohms. 

A low noise shielded probe cable is so flexible that the lightweight probe head stage will always stay where you want it. 

HEADSTAGE ELECTRODE CONTROL SWITCH

The ELECTRODE control switches provide a unique combination of microelectrode termination's. A push of the button changes the 2400A system from(1) a high current stain generator for marking recording site to a, (2) controlled positive or negative ideal current source up to 1000nA to (3) a low noise neutralized preamplifier and an audio monitor, or (4) gives you a direct connection to your microelectrode for any future need that you may encounter. All this without ever touching the probe or the microelectrode. 

CURRENT PUMP

The CURRENT PUMP provides a precisely regulated Current from 0 to plus or minus 1000 nA for injection of dyes or drugs from the microelectrode by iontophoresis. The currents can be injected through the probe into the microelectrode by pushing the ELECTRODE switch to the CURRENT PUMP position. If the need should arise for the CURRENT PUMP to be terminated in an electrode other than the recording electrode, its output current is always available at the AUX PUMP OUT BNC connector. With the PUMP LEVEL switch set to the INTERNAL position, the current magnitude is set by the ten-turn digital readout dial. the polarity is set by the PUMP POLARITY switch. The OFF position of this switch programs the ideal current generator to zero nA output, this is a quick means of going form the dialed CURRENT PUMP level to zero nA. 

Supplying an external bipolar analog signal into the EXT REF BNC jack with the PUMP LEVEL switch set to EXTERNAL allows the ideal current source to be programmed externally by the magnitude and polarity of the reference signal. (Interfaces directly with the D/A converter on any computer. 

PREAMPLIFIER

• IMPEADANCE (Z) TEST: 100mV/megohm 
• NEUTRALIZATION: 15 turn control located on probe. Range is 0 to 100 pF. 
• INPUT IMPEDANCE: Greater than 10,000 Megohms 
• INPUT CONNECTOR: Min. co-ax 
• OUTPUT: 10 ohms, 20 volt peak to peak, BNC connector 
• GAIN: 50, 100, 200 500, 1K, 2K, 5K, 10K 
• OVERLOAD RECOVERY: Recovery is very fast, usually one-half to a few milliseconds except for just after Stain, recovery is then 20 to 40 seconds. 
• NOISE: Due to Amplifier and Source Resistance (takes into account current and voltage noise), RMS and Peak to Peak (P-P) 

Bandwidth	Source Resistance
	100 Kohm	1 Megohm	10 Megohm
1 Hz to 1 K Hz	1.6 uV RMS	4.5 uV RMS	16 uV RMS
	8 uV P-P	22 uV P-P	80 uV P-P
1 Hz to 10 KHz	4.5 uV RMS	12 uV RMS	40 uV RMS
	22 uV P-P	60 uV P-P	200 uV P-P

• CALIBRATE GENERATOR: 100 mV @ 1%, Peak to Peak Square Wave, 150 Hz 
• LINE NOTCH FILTER: Standard 60 Hz, (optional 50 Hz.) The Rejection ratio is 200 to 1 or 46 dB. 
• HIGH FREQUENCY FILTER: Activate 20dB/decade, pushbutton switch selection 3 dB points are; 100, 300, 1000, 3K, 1OK, 30K, and 100KHz. 
• LOW FREQUENCY FILTER: Active 20 dB/decade, Push button switch selection 3 dB points are; 0.3, 1.0, 3.0, 10, 30, 100, and 300 Hz 
• AUDIO MONITOR: An internal audio power amplifier monitors the Preamplifier Output. Sound level is controlled by the Monitor control. Output is through two Binding Posts located on rear panel, An 8 ohm speaker is recommended. 

CURRENT PUMP

• PUMP LEVEL:EXTERNAL: An analog voltage between minus 10 to plus 10 volts into the rear panel BNC jack generates a current between minus 1000 nA, to plus 1000 nA. INTERNAL: The INTERNAL position enables the 20 turn digital dial current setting. The dial is read out in nA, and has a range of 0 to 1000 nA. Polarity is determined by the PUMP POLARITY Switch. 
• STAIN: A POSITIVE (for metal electrodes) Or NEGATIVE (for Glass electrodes) voltage of 15 volts limited by 10,000 ohms is fed into the electrode. 
• ELECTRODE (PROBE MODE): A four station push button switch selects the mode of operation by connecting the probe input connector to the four functions via a reed relay located in the probe. The Four functions are: 
• CURRENT PUMP: The CURRENT PUMP section of the instrument is connected through the probe to the electrode. The CURRENT PUMP is always available through the AUX PUMP OUT BNC jack. 
• PREAMPLIFIER: The probe and audio monitor amplifier are connected to the electrode. 
• EXTERNAL: The electrode is connected to the EXTERNAL BNC jack. This position gives direct access to the electrode for passage of any voltage or current 
• STAIN: The high level STAIN current is fed to the microelectrode 

• POWER: 115v AC, 60 Hz, 6 Watts (optional 230v AC, 50 Hz, 4 Watts) 
• DIMENSIONS: MAINFRAME: 43.2 cm W (17") X 34.3 cm D (23 1/2") X 14 cm H (5 1/4 ") (for Rack mounting, handle and brackets make width 48.3 cm (19") and removal of feet make height 13.3 cm (5 1/4 ") PROBE: 5.7 cm (2 1/4 ") X 3.2 cm (1 1/4") X 2.5 cm (1") less mounting plate. Detachable rod is 0.63 cm dia. (1/4 ") X 7.6 cm long (3"). Probe to Mainframe cable is 7 conductor, low noise shielded, 3 meters long (10'). WEIGHT. 5 Kgr. (11 pounds)