The "Make Before Break" connection for audio interconnects (MBB configuration)

A common problem we encounter in audio has to do with audio interconnections. The standardized connectors are the well known RCA coaxial ones. These connectors suffer from an important property. When a connection is first made, the positive pole is connected first, and then the negative one afterwards. At the time interval where the positive male pole touches the positive pole of the female plug and when the negative is not yet connected (when you first insert your plug), hum is introduced from the lack of signal ground, which passes all the way through the amplifier, amplified and then ends to the speakers. This hum is so loud, that in extreme cases it can cause damage to your speakers, not to mention your ears, if the amplifier volume control is accidentally set to maximum.

Unfortunately, the audio industry uses RCA connectors for many decades and includes them as standards in every audio equipment you buy. But there is a better connector to use for audio interconnections, the BNC. The BNC is a 50 ohm connector used on radio frequencies and old computer networks and it's construction does not allow the positive pole to be connected first when the plug is inserted. In any case, first the GND (shield) is connected and then the positive pole. This does not introduce the hum of RCA connectors.

The BNC has also another important advantage. It has two little pins externally on the shield, which are used to lock the male connector to the female one and thus to ensure the connection will never be accidentally broken. Its internal positive conductor construction is also less immune to contact failures, even in the worst quality BNC connectors. Besides, standard quality BNC connectors are as cheap as RCA ones. Even if the BNC is used as an option to the LSC configuration, the shield of the connector still provides mechanical stability and keeps the cable firm on the audio equipment.

You can use BNC connectors for your speaker cables too. In fact this has the advantage that you do not touch the internals of the connector or the cable poles with your hand and this ensures that no dust from your fingers will be introduced to the internals of the connector. The BNC ensures also that no dust from the air will intrude the internals of the connector, as the central conductor is well hidden into the connector body and the external body touches the matching connector both from the inside and the outside. There is only a drawback in using BNC for your speaker cables. The BNC was a thin central conductor and cannot handle large currents, so you can only use them in low power amplifiers, I do not know exactly what is the maximum power it can handle but it seems to me like it is the same power you can use an RG223 coaxial for, as they have about the same internal conductor thickness. Anyway the BNC power handling specs are 80 Watts at 1GHz, so for audio I would expect at least something similar, which is ok for most room listeners.  For greater powers there are other RF connectors that you could use and it is only a matter of taste and properties of each connector to experiment with.

With the advance of audio technology and the hunger for more high end equipment, companies have produced very high quality RCA connectors sold at extreme costs and they seem to ignore the fact that there may be better connectors for audio. Because BNC are not used by companies for audio, even the highest quality (non magnetic military silver plated etc.) cost less than the highest quality RCA.

 


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