I am an accountant not an electrical engineer so please don’t laugh at my questions.
I have an in-dash radio/cd player made by Blaupunkt (BMW CD43).
I want to convert the 4 pair of speaker-level outputs to a balanced line for transmission to a Zed Audio ESX 120.4 amplifier.
I do not have the schematic for the input stage(s) of the ESX unit.
If I understand correctly, a balanced connection uses three wires. One wire is chassis ground and the other two wires are for the signal with the signal equal in amplitude in each of these two wires, but opposite in phase. What is balanced is the impedance on the two signal wires in this configuration.
I want to connect a BMW CD43 head unit that has bridge tied load audio output. The outputs come from two ST Microelectronics TDA7376B audio amplifier IC's. They are rated to put out a maximum of 40W per channel.
The datasheet is here, if you are interested:
http://www.st.com/stonline/products/...7/tda7376b.pdf
The outputs carry a common-mode voltage of ~0.5*V supply, and the - output terminal is inverted relative to the + terminal. It is not a true balanced setup because there is no dedicated neutral line that they are referenced against. The offset between the BTL outputs is ~100mV (spec sheet says it can be up to 125mV). 125mV into a 4-Ohm load is ~16mW (0.016W).
To use these outputs in a balanced line, I intend to add dedicated neutral wires in the interconnect cables.
On the destination end the Zed Audio ESX 120.4 is designed to accept balanced input(s). It uses two 6-Pin Mini DIN female connectors (which, according to the manual, each carry both pairs of a stereo channel). This would be Front Left +, Front Left -, Ground, Front Right +, Front Right -, Ground. So the dedicated neutral wire is predetermined by the schematic on the amplifier end.
I think my questions a
1. Where should the two dedicated neutral lines terminate on the BMW CD43 head unit end? Those are to be radio chassis grounds?
2. How can I ensure the balance of the impedance in each signal pair?
If I have posted this to the wrong forum will the moderator please move?