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Current Sensitive Preamplifier

10-9A/V MAX DC-200KHZ



 The model 181 is a current-to-voltage preamplifier of low noise and low input impedance designed to amplify the extremely low low currents encountered in such areas as photometry and semiconductor research. In photometric applications the low input noise allows the use of photo detectors with dark currents as low as 10-14 A/root Hz, while the wide frequency range permits high modulation frequencies to avoid 1/F noise and power-line pick-up.

The unit has a high dynamic range, allowing small AC currents to be amplified without overload in the presence of quiescent (DC) detector currents up to ten times the current to voltage converter setting. In semiconductor applications its low input impedance permits the actual bias voltage applied to the device under test to be measured without having to correct for the effects of back bias.

Six switch-selectable gain settings from 10-4 A/V to 10-9 A/V are available and the instrument has a useable frequency range from DC to 200 kHz. A signal monitor connector is provided on the rear panel and there is an overload indicator light on the front panel.

Bias Control
A bias control (accessible through an opening in the bottom of the unit) allows the application of a detector bias voltage at the input connector in the range 0 V to -5 V, with a nominal source impedance of 10-5/S, where S is the selected sensitivity. For example, if the sensitivity is set to 10-7 A/V then the source impedance will be 10-5/10-7, or 100 W. In some cases it may prove convenient to use this bias control to cancel the effect of DC bias accompanying the input signal.

DC Zero Control
A second control, also accessible through an opening in the bottom of the unit, allows the internal electronics to be DC zeroed.

The unit can be powered from an external low voltage, a lock-in amplifier via a suitable power cable, or the models PS0055 or PS0056 remote line power supply modules.

Frequency Response (typical):  181fres.gif (13894 bytes)
Input Impedance (typical) :  181inpz.gif (11212 bytes)

Noise Current (typical) :  181inoi.gif (12029 bytes)

Peak Input Current (typical)

Gain A/V Frequency response DC to Maximum (peak) Input Current
10-4 200 kHz 1 mA
10-5  200 kHz 100 A
10-6 100 kHz 10 A
10-7 50 kHz 1 A
10-8  10 kHz 100 nA
10-9  1 kHz 10 nA


Gain  10-4 A/V to 10-9 A/V in six ranges.
Overload Indicator  Indicates that instantaneous (DC plus peak AC) current has exceeded amplifier capability
Monitor 600 W rear-panel BNC connector permits monitoring of the input signal
Output Attenuator Provides optional 1:10 attenuation of output voltage
Signal Output Level 6.5 V rms maximum
Signal Output Impedance 1 kW nominal
Power Requirements 15 V or 24 V at 30 mA
Dimensions 4.5" wide x 6.6" long x 2.7" high (114 mm wide x 168 mm long x 69 mm high)

Shipping Weight

2.2lbs (1 kg)

Equipment Notes:

Unit is in excellent physical and electrical condition.


This item is sold with a 3 Day Satisfaction Guarantee.  So bid with confidence.
As our many customers will attest, we will do our very best to resolve any customer problems. But our official policy is:

This item comes with a 3 day right of return policy.
All returns must be made within 3 days of receipt.
All warranties are void if the calibration / warranty seals are broken.
Equipment must be shipped correctly and returned with all accessories.
Customer is responsible for all shipping charges on returns.
Foreign Buyers please be aware: We offer no warranty or returns on items shipped outside the USA

Payment, Shipping & Bidding:

Buyer will pay $25.00 packing and shipping in the continental United States. Payments accepted are Paypal, cashiers checks and money orders only.  No international buyers unless Paypal verified.  Please feel free to contact us if you need other arrangements.

We will make every effort to ship within 24 hours of receipt of payment. We ship with FedEx & UPS only. We will be glad to ship with other carriers using the purchasers shipping account. Please contact us to make any special shipping arrangements. For shipping rate research, our shipping address is Boulder, CO USA ---- Zip Code is 80305.

Many of our auctions have a set packaging and shipping fee.  This set fee makes the transaction easier and allows the purchaser to send payment at once without having to wait for a shipping total.  This is our best guess on an unpackaged item.  Please consider the total with shipping when you are bidding.

Foreign buyers: Unless special provisions have been made, you are responsible for making your own shipping arrangements and all costs related to customs, duties & special packaging requirements. Please do not ask us to quote you international shipping rates. Use the address information above to research you own shipping rates. You can email sales@ascentconcepts (no spam) .com to get the packaging fee, package weight and size for your research. Items sold outside the USA are sold as is.

Bidders - with no feedback or less then 80% positive feedback must contact us through the eBay email system before placing a bid. We will reply through the same system, documenting that you have been approved to bid. If you do not follow these procedures, your bid will be cancelled.  All other bidders, bid with confidence.


About Us:

Ascent Concepts and Technologies is a Research & Development Lab. As a service to the companies and institutions we work with, we broker their excess equipment & act as application specialists on their new equipment needs. We are now offering quality used equipment to the public with the same level of professionalism and service.

Please feel free to email at thomasknox@ascentconcepts (no spam) .com or call Thomas @ 1-303-554-0307 with any Technical questions. Please feel free to email at waltwhite@ascentconcepts (no spam) .com or call Walt @ 1-720-276-8288 with any Shipping or Logistical questions. We make every effort to evaluate and guarantee our equipment. Although we do not provide NIST traceable calibration, we do have extensive in house calibration equipment and make every effort to test and verify performance on equipment we sell. However we do not warranty any items shipped outside the USA.


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The equipment shown is a representation only.  We often have multiple units in stock so please email us with your needs.  We have a large inventory and can usually find any test and measurement item in a short time frame.------Inquires