Balanced Drive And Single-Ended Drive - M2TECH MARLEY User Manual

M2Tech
marley
DUAL-DRIVE CLASS-A HEADPHONES AMPLIFIER
REVISION P .A – OCTOBER 2013 www.m2tech.biz
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7. Balanced Drive and Single-ended Drive

Most headphones are fitted with a 3-pole cable (and related connector), one of which
is used for common return, one for left channel send and the third one for right
channel send.
On the other hand, some headphones are provided with a 4-pole cable and
connector: two poles for left channel drive and two poles for right channel drive.
Headphones of first type can only be driver in single-ended mode, whereas the
amplifier driver one of the wires running to each speaker and the other wires are
connected to the amplifier's ground.
Headphones of second type can be driver in balanced mode, in which two amplifiers
drive one wire of each speaker.
The first setup is cheap as it only requires one stereo amplifier, but implies limits to
the sound quality, as the two channels signals may partly mix due to the non-zero
impedance of the common return wire. This leads to reduced channel separation and
a slight dynamic loss.
These problems may be reduced by separating the returns to round, thus improving
the sound quality.
A further improvement is obtained by "lifting" from amplifier's round the return wire of
each speaker: this can be accomplished, as mentioned earlier in this manual, by
using a bridge amplifier (that is, an amplifier provided with two output stages
operating in push-pull). In this setup, called "balanced" the two speakers cannot
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