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Old 5th November 2015
Gear Maniac
I am putting the finishing touches on the front panel graphics, then production starts. Front panels are already made, they just need graphics.

Regarding the selection of transformers for the Radial version of the Jensen Twin Servo, here is my speculation regarding the input transformer that they are using (total speculation, don't bet the farm on it, YMMV, Peter Janis can certainly correct me):

I happened to be looking at the Hairball Audio site last weekend and noticed that they have a mic preamp kit that has a Jensen "JT-16-PCJR" mic-input transformer as an option. That was the first reference I have seen to the JT-16-PCJR. There is no sign of it on the Jensen site. "PC" likely means it has p.c. pins, not wires. That is the Jensen naming convention. Hairball documentation for the kit shows that there is a place on the circuit board for a pc-mount transformer. "JR" likely means it is a "junior" (smaller) version of the original JT-16-A and JT-16-B. The JT-16-B is what I use in all of my mic preamps, including the original Jensen Twin Servo.

Based on the component outline on the Hairball circuit board, the "JR" version appears to have the same square package as the Jensen JT-115K-EPC (p.c. mount version of the JT-115K-E), which would mean that it uses a smaller bobbin size and smaller lamination size than the JT-16-A and JT-16-B. As a result, the "JR" version would have a lower "maximum input level" compared to the full-size JT-16-A and JT-16-B. Without a data sheet it is hard to say how much lower the maximum input level is, but likely at least a few decibels.

Unless ionian can remember what the transformers looked like on the Radial prototype at AES, and/or Peter Janis jumps in to confirm, my theory will be that it is the JT-16-PCJR that Radial is using in their Jensen Twin Servo 500.

As mentioned earlier, I am using the JT-16-B and the JT-11-DM in my Jensen Twin Servo 500. No problem for me fitting them into the design with room for a shield assembly around the circuit board.

Thank you.

John Hardy
The John Hardy Co.
The John Hardy Co. Home

Last edited by John Hardy; 6th November 2015 at 12:19 AM.. Reason: Spelling corrections. Apologies to Peter!