J99 Input Transformer question

[davidmen]

Hi Tim, since the op amps (the 990 and the sc99) are low impedance inputs, the lundahl 1538xl seems to be some medium to high impedance input tx, compared with the JT -16; Are the 1538xl raising the noise floor a little bit since the 1:5 ratio? Don't get me wrong, the 1538xl it's one of the best input tx, my concern is about the noise floor. Thanks.

[tpryan]

The 1538XL can be connected 1:5 or 2:5. Normal operation on the J99 is 2:5, not much different than the 2:4 of the JT-16. Jumpering for 1:5 gives another 6dB of gain for very low-z sources, something you can't do with the JT-16. Also, J99 input impedance is a slightly old-fashioned 1200 ohms, which gives somewhat better immunity to real world high impedance noise sources.