4.3.V25 Balanced Wiring
Multi-Board Audio Data Link
The V25 is designed to allow multiple V25 boards to be daisy-chained together for multi-channel audio. The top most board in a daisy-chained multi-board scenario is designated the master and other downstream boards are slaves.
As the names suggest, the master V25 board is in charge and receives control inputs, drives the visual display, and passes commands over to first slave board in the daisy-chain. The first slave board then passes commands on to the next slave board.
The master and slave boards are powered individually from a single common power supply and communicate with each other via a simple 2 wire serial data (UART) link.
Any V25 board can be the master. No special jumpers or settings are required.
Dual Board Balanced Audio
Balanced stereo audio requires two V25 boards with the data link connected between them and the audio inputs and outputs wired as described herein.
Master To Slave Control Connection
The master/slave designation is determined by how the communications link is connected between the 2 boards. The 2-wire serial data link on the master board is always connected to pins TX1/RX1 and the serial data link at the downstream slave board is always connected to TX2/RX2. This is shown in the diagram below.
If there are multiple downstream slave boards the same TX1/RX1 to TX2/RX2 connection pattern repeats between each paird of slave boards. In this fashion each downstream slave board is subservient to its upstream neighbor.
External Control of Master
Users can opt to control the master V25 via any external control device equipped with a UART port by connecting the external control’s TX/RX signals to the master’s RX2/TX2 pins respectively.
Users should refer to the V25 UART Commands section found elsewhere in the online production documentation for more details on the UART commands and protocol.
Balanced Wiring | 3 Pin XLR
Balanced XLR wiring is unavoidably more complex than single-ended RCA.
First, you are dealing with three (3) terminations per channel; two signals (pin 2 and pin 3) plus one shield/ground (pin 1). Next, you have both male (output) and female (input) type connectors each of which reverse the position of pins 1 and 2 with respect to the other while pin 3 remains thankfully unchanged. Last, but not least, some diagrams show the pins in a front view while another may use a rear view.
For purposes of your sanity and this guide, assume all XLR connectors herein are rear view only.
Connecting balanced audio signals and ground to the V25 can be challenging for the simple reason that it’s a bit complex and thus it’s easy to make a mistake.
The correct way to wire balanced audio to the V25 is shown below in two different diagrams. The first is a more abstract schematic representation while the second looks closer to actual wiring to the boards. In either diagram we only terminating a single input and a single output to the left and right channels.
Before diving in with wiring your V25 boards, we strongly recommend you study these diagrams until you understand the wiring scheme represented here. The wiring scheme is summarized in the following bullet points:
- Master board handles the A/+ phase of both the right and left channels
- Slave board handles the B/- phase of both the right and left channels
- All grounds (including the pin 1’s) get wired to a single common “star ground” point somewhere within the enclosure
The wiring diagram shown below is consistent with the schematic shown above and is provided to show where the wires need to be connected on the actual V25 boards. Note that this is only for a single input so the input is connected to the solder pads labeled RI1 and LI1 on each board. For additional inputs you would terminate the wires to solder pads RI2 and LI2 etc.
Alternatively you could also make the same terminations via the J5 pin header or some combination of the J5 header and the solder pads.
Lastly, 2 solder pads are provided on the V25 board for both the output (RO and LO) and the signal ground (RG and LG). This is simply for convenience.