Connecting a UTC A11 for a passive DI

[rstefan]

Hello,

I'm designing a simple passive DI using a UTC A11 transformer. I'm having trouble understanding this sheet I found online regarding the transformer's terminal arrangement:
http://www.clarisonus.com/Archives/Trans/UTC_conn.pdf

I want the primary side to have an impedance of 200 ohms, which means I would have to use terminals 2 and 4 as my positive and negative output terminals of my DI (to go from hi-Z to lo-Z). But then it says something about "join 3-C.T." which I'm kind of confused about since terminal 3 IS the center tap for the primary coil. Are they telling me to connect terminal 3 to terminal 2 or 4? Or are they asking me to connect terminal 3 with terminal 7, the center tap of the secondary coil?

Let me know if anyone has any ideas

 

[PRR]

Welcome.

The CT is there if you need it. You do NOT want it (in 99.44% of studio/stage work). Hard-balancing is occasionally useful when working under a transmitter, or for running Phantoms (signaling, power, or extra voice pairs).

 

[Bill Wilson]

The primary connections in PRR's post are correct. You do not need to use pi3 which is a center tap.
This is used as the output to the input of the microphone pre amp.

What is labeled secondary is actually the hi impedance input of the di box & should be connected as follows: hi Z input to pin 7 of the transformer & ground is connected to pin 10. This is the basic DI box connection.

One added feature: connect the ground lead coming from pin 10 of the transformer to the arm of a single pole single throw switch, the same lead is connected to the sleeve of the input jack. One end of the switch is connected to the case vof your DI box; the other end of the switch is left with no connection. Thjs is known as a ground lift switch.  Its function follows: the normal position is to have the ground return from the hi impedance input jack connected to the case of the box. If you are experiencing hum from the instrument going thru the box throw the switch the other way, disconnecting the instrument ground from the case of the box; this should eliminate the hum. If it does not then either the sheiding of the cable connecting the instrument to the box is insufficient or the problem lies with the pick up itself.