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Microphone Input Transformers


JT-13K7-ATB Picture Jensen is Offering a New 3/8" Threaded Bushing Mount
for the following Microphone Input Transformer Models:
JT-16-A, JT-13K6-C, JT-13K7-A, JT-115K-E and JT-115K-E60

Simply add "TB" to the standard part number:
Example: JT-13K7-A becomes JT-13K7-ATB
There is a $2.50 charge for this option in small quantities
(call for quantitiy pricing)


Microphone preamp designs incorporating Jensen Input Transformers offer several
advantages over the more commonly used, inexpensive "transformerless" designs:
1) Superior Common Mode Interference Rejection
2) Superior Radio Frequency Interference Rejection
3) Ideal impedance matching of source to amplifier
4) Elimination of input coupling capacitor distortion


Jensen manufactures Microphone Input Transformers in many step-up ratios in order to
provide the best possible noise performance with any type of active amplifier device.


Microphone Input Transformer Selector Guide

All have a 30dB Magnetic Shield can and a single Faraday Shield (except * which have two shields)
Mechanical Drawing for Right Angle Mtg. Brkt. - Keystone #620
Mechanical Drawing for VR-3 and VR-4 Mtg. Clamp

Model # Price Impedance Ratio Turns Ratio Max 20Hz Input THD 20Hz THD 1kHz 20Hz - 20kHz re:1kHz -3dB BW
JT-MB-CA* $ 150:150 1:1 +2dBu 0.045% 0.001% -0.10dB -0.04dB 180kHz
JT-MB-CPCA* $ 150:150 1:1 +2dBu 0.038% 0.001% -0.10dB -0.04dB 170kHz
JT-16-A $ 150:600 1:2 +10dBu 0.025% 0.001% -0.06dB -0.00dB 220kHz
JT-11K8-APC $ 150:1.8k 1:3.5 -2dBu 0.070% 0.002% -0.17dB -0.06dB 80kHz
JT-13K6-C $ 150:3.5k 1:4.8 -2dBu 0.070% 0.002% -0.30dB -0.01dB 125kHz
JT-13K7-A $ 150:3.8k 1:5 +7dBu 0.030% 0.001% -0.08dB -0.08dB 120kHz
JT-110K-HPC $ 150:10k 1:8 -2dBu 0.045% 0.001% -0.19dB -0.08dB 100kHz
JT-115K-EPC $ 150:15k 1:10 -2.5dBu 0.065% 0.001% -0.26dB -0.13dB 90kHz
JT-115K-E $ 150:15k 1:10 -2.5dBu 0.065% 0.001% -0.26dB -0.13dB 90kHz
JT-115K-E60
(2 Shield Cans)
$ 150:15k 1:10 -2.5dBu 0.065% 0.001% -0.26dB -0.13dB 90kHz

TRANSFORMER SELECTION

To determine the proper ratio transformer for your application, you will need to know the Voltage Noise and Current Noise of the active amplifier device to which the secondary of the transformer will be connected. If you divide the Voltage Noise by the Current Noise of the device you will get a value in Ohms. This value is the Optimum Source Impedance for best noise performance using that particular amplifier device. Select the transformer whose secondary impedance most closely matches the calculated value.

Example: An AD797 has an input Noise Voltage of 1.2nV per root Hertz Max. @ 1kHz and an input Current Noise of 2.0pA per root Hertz. This gives an Optimum Source Impedance of 600 Ohms. The proper choice of transformers for this device would be either the JT-16-A or the JT-16-B.

Special Note for Vacuum Tube Applications

If the above calculation is performed for Vacuum Tubes, the value obtained will normally be much higher than the secondary impedance of even our JT-115K-E transformer. We do not manufacture Microphone Input Transformers with ratios higher than 1:10 due to the limited bandwidth that is possible in designs of this type. The JT-115K-E will work very well in most Vacuum Tube applications.



Jensen Transformers, Inc., 9304 Deering Ave. Chatsworth, CA 91311
Voice: (818) 374-5857 Fax: (818) 374-5856
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