B.M.C. Pure Dac Gebruikershandleiding - Pagina 11

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Balanced Headphone Drive

What is Balanced Drive?

In all stereo headphones there is a driver for each ear which is directly wired to the headphone plug. A

headphone is a passive device, so an amplifier must supply the electrical energy to make it work.

Most amplifiers have a single active output delivering the music signal related to a static ground. The

ground is shared for both channels, for the power supply and the other components using electricity inside

the device driving the headphones. So the ground is effectively contaminated with noise not belonging to

the music signal.

In case of a balanced amplifier beside the active signal per channel, there is another active but mirrored (or

inverted) signal. Whenever the "normal" signal output is positive the inverted output is negative and vice

versa. The summary of the inverted and the non-inverted signal is always 0.

The headphone driver now gets connected between the non-inverted and the inverted signal.

Ü Both signals carry music only, so the ground contamination becomes irrelevant.

Ü The headphone "sees" double the signal voltage change within the same time, which means double

signal speed.

Ü One-sided (even) distortions are effectively cancelled by the nature of the circuit's architecture.

Ü Power supply noise contaminating both balanced channels in the same way, cancels itself.

Headphone Wiring Requirements

Any headphone with 4 separate wires (2 x left, 2 x right) can be configured for balanced drive. One simple

indicator is a cable which splits in the middle and connects to each ear individually. In this case just the

connector has to be changed from a 3-pole ¼" stereo plug to a 4-pin XLR plug (for pinning: see front panel

description).

Headphone manufacturers are increasingly becoming aware of the benefits of balanced drive and the

availability of ready solutions is growing continuously. Several specialized headphone shops offer service

for replacing the headphone wiring with balanced wiring of higher cable quality.

Adaptors

An adaptor cable might be useful for using the same headphone balanced with the PureDAC and e.g.

unbalanced with a mobile device. Please be aware of the following points:

Ü There is no such thing like a working adaptor from ¼" stereo plug to a 4-pin XLR plug. Such adaptor will

definitely damage the headphone amplifier!

Ü An Adaptor from 4-pin XLR plug to ¼" stereo plug or 3.5mm stereo plug is very easy to make. Please ask

your dealer.