M2TECH Marley - Manual (Page 29)

marley
DUAL-DRIVE CLASS-A HEADPHONE AMPLIFIER / PREAMP
REVISION 1.0 – NOVEMBER 2013
Copyright © 2013, M2Tech Srl
29
M2Tech
www.m2tech.biz
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.
Optionally, 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 the first type can only be driven in single-ended mode, whereas the
amplifier drives one of the wires running to each speaker and the other wires are
connected to the amplifier’s ground.
Headphones of the second type can be driven in balanced mode, in which two
amplifiers drive one wire of each headphone speaker.
The first setup is a low cost manufacturing option as it only requires one stereo
amplifier. If this low cost manufacturing option is used, this severely limits 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 ground, thus improving
the sound quality.
An additional improvement is obtained by “lifting” from the amplifier’s ground 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