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

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.

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.

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