BeePre Input Transformer Modification

01 Sep

BeePre Input Transformer Modification

2014/09/01 by Joshua Harris

First, buy the necessary supplies:

2 x CMLI-15/15B (CMLI-15/15B2 will also work) transformers, ordered from www.cinemag.biz. Be sure to order as a single 3/8″ stud

From www.mouser.com:     
2 x 22KΩ 1/4W resistors (Mouser 660-MF1/4DC2202F)
2 x Neutrik female XLR jacks (Mouser 568-NC3FD-L-1)
1 x 5-lug terminal strip (Mouser 158-1005)

01-hardware

Remove the plastic hole covers. Trim the wires off the RCA Jacks closest to the transformer holes. Mount the XLR jacks with the existing hardware and add a 5-lug terminal strip to the back hole of the front XLR jack. The terminals are numbered from front-to-back.

02-xrfrm_mnt

Mount the transformers using the hardware supplied with the transformer — insert the post from the top side of the chassis and secure below with the lockwasher and nut. Do not fully tighten the transformers.

03_red-brown

Attach and solder the red wires to pin 2 of the closest XLR jack.

Attach and solder the brown wires to pin 3 of the closest XLR jack.

04_black_white

Attach and solder the black and white wires to the ground tab of the closest XLR jack.

05_green_brownCAT5

Attach the green solid wire to 1U, the green striped wire to 2U, the brown solid wire to 4U and the brown stripe wire to 5U. Do not solder any of these terinals

06_22Ks

Attach a 22KΩ 1/4W resistor between 1U and 2U. Do not solder.

Attach a 22KΩ 1/4W resistor between 4U and 5U. Do not solder.

07_yellow_orange

Attach and solder the orange wires to 1U and 4U. Attach and solder the yellow wires to 2U and 5U.

Return the BeePre to your system and power the system on. Switch the selector to the position for the balanced input and listen for hum. Rotate the transformers to minimize hum.

Enjoy your balanced input!

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