Balanced power audio amplification system

A configuration of audio system components, utilizing standard amplifier components, wherein the audio system remains balanced through the speaker input terminals. For each channel of the system, a preamplifier produces a balanced output signal. Two power amplifiers or similar devices are conventionally configured to accept positive and negative input signals. The negative signal output of the preamplifier is connected to the positive input terminal of one of the power amplifiers, and the positive output signal of the preamplifier is connected to the positive input terminal of the other power amplifier. The negative and ground input terminals of both power amplifiers are connected to system ground. The connections between the preamplifiers and the amplifiers may be effected by a unique cable designed for this purpose. The positive output terminal of one of the power amplifier is connected to positive input terminal of the speaker, while the positive-output terminal of the other power amplifier is connected to the negative input terminal of the speaker. The negative output terminals of each power amplifier "floats", unconnected externally to the speakers.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to audio signal transmission and 
amplification systems, specifically to an improved configuration of an 
output channel in an audio signal amplification system which increases the 
power delivered to the speaker and reduces audible noise. 
2. Description of Relevant Art 
In audio signal transmission and amplification systems it is generally 
desirable to increase the power of the audio signal that is delivered to 
the speaker while simultaneously increasing the signal to noise ratio. 
Noise and signal distortion can be introduced by a variety of sources 
including the system ground and environmental factors. 
Sophisticated audio systems often use components that produce a so-called 
"balanced" signal to increase power while at the same time reducing or 
eliminating noise and distortion. In balanced systems, the original audio 
signal is used to create two signals which are substantially identical to 
the original audio signal but which are 180.degree. out-of-phase with each 
other. The phases may be used together to produce an amplified signal that 
is a function of the difference in the amplitude of the two phases. The 
amplified signal is thus effectively independent of the system ground and 
any noise or distortions introduced by the system ground: the quality of 
the amplified signal depends only on the relationship of the out-of-phase 
signals to each other. Therefore, noise is reduced or eliminated in a 
balanced system since only the signal components that are opposite each 
other in the two signals are fully amplified. Common-mode signals, which 
may be caused by environmental factors, appear equally and with the same 
polarity on both out-of-phase signals, and are eliminated completely in an 
ideal balanced system because such common-mode signals have no effect on 
the difference in amplitude between the out-of-phase signals. Furthermore, 
if noise or distortion appears on only one of the out-of-phase signals, 
the magnitude of the noise or distortion is reduced, as it is not fully 
reflected in the difference between the signals. Thus the use of balanced 
signals results in an increase in the signal-to-noise ratio. 
Audio signal transmission systems have usually been "balanced" through the 
power amplifier, such that the preamplifier produces the balanced signals 
which are then amplified by the power amplifiers. In standard systems the 
connections between the power amplifiers and the speaker have been not 
been balanced. The positive and negative output terminals of the power 
amplifiers are simply connected to the positive and negative input 
terminals, respectively, of the speakers. Some high-end amplifiers have 
been balanced through the speakers by using connections internal to the 
amplifiers; however, these amplifiers are expensive, and are non-standard 
components. 
One method that has been used in some systems to increase power at the 
speaker using standard components is known as "bridging". In bridging, 
same polarity output terminals of two power amplifiers are connected to 
each other, and the terminals of one such power amplifier is connected to 
the positive and negative input terminals of the speaker, which 
effectively results in the output signals of the two power amplifiers to 
be additively applied to the speaker. While this method does increase the 
power delivered to the speaker, it does not eliminate noise, and the input 
signal to the speakers is dependent upon system ground. 
SUMMARY OF THE INVENTION 
In view of the foregoing, the principal objects of the present invention 
are 
(a) a new configuration of audio system components, utilizing standard 
amplifier components and unique audio cables, such that the audio system 
remains balanced through the speaker input terminals, thus reducing noise 
and increasing the power delivered to the speakers; and 
(b) a connection apparatus for effecting such configuration. 
According to the present invention, for each channel of the system, a 
preamplifier or similar device produces a balanced output signal at the 
preamplifier output terminals. Each channel requires two power amplifiers 
or similar devices, which are conventionally configured at their inputs to 
accept positive and negative input signals and system ground. The 
preamplifier and the power amplifiers are configured to cause the negative 
signal output of the preamplifier to be connected to the positive input 
terminal of one of the power amplifiers, and the positive output signal of 
the preamplifier to be connected to the positive input terminal of the 
other power amplifier. The negative and ground input terminals of both 
power amplifiers are connected to system ground. 
This connection may be achieved using a unique connection cable having 
input connectors suitable for connection to the preamplifier output 
connectors and two sets of output connectors each of which is suitable for 
connection to the input connectors of a power amplifier, and which effects 
the appropriate connections, as described above, between the terminals 
positive, negative and ground terminals, which are housed in the 
connectors. 
The output connectors of the each of the power amplifiers may also be 
conventionally configured, comprising positive and negative output 
terminals, and may be housed in conventional connectors. The speaker input 
terminals may be conventionally configured, with positive and negative 
input terminals, and also may be housed in conventional connectors. The 
positive output terminal of one of the power amplifier is connected to 
positive input terminal of the speaker, while the positive input terminal 
of the other power amplifier is connected to the negative input terminal 
of the speaker. The negative output terminals of each power amplifier 
"floats", unconnected externally to the speakers. The connections 
described may also be effected by a cable designed for this purpose. 
As a result of this configuration, a balanced signal is delivered to the 
speaker inputs, significantly increasing the power delivered to the 
speaker, using conventional amplifier components and reducing system 
noise.

DETAILED DESCRIPTION OF THE DRAWINGS 
FIG. 1 shows the configuration of one channel of the system according to 
the present invention. Preamplifier 101 is suitable for producing a 
balanced output signal of substantially identical signals which are 
180.degree. out of phase, at its positive and negative output terminals 
102, 103. It should be noted that the preamplifier is acting as a source 
of a balanced output signal, and any source of balanced output signals may 
be used in its place. The positive output terminal 102 of the preamplifier 
101 is connected to the positive input terminal 111 of amplifier 110. The 
negative output terminal 103 of preamplifier 101 is connected to the 
positive input terminal 121 of amplifier 120. The ground output terminal 
104 of the preamplifier 101 is connected to the negative input terminals 
112, 122 and the ground input terminals 113, 123 of the amplifiers 110, 
120. The connection may be effected by a specialized cable (not shown), as 
described in the text associated with FIGS. 2 and 3. It should be noted 
that although it is advantageous to effect the connection of the negative 
input terminals 112, 122 and ground input terminals 113, 123 to system 
ground by way of a specialized cable so that conventional amplifiers may 
be used, it would also be possible to make such connections within the 
amplifiers themselves. 
Each amplifier is suitable for producing an output signal from the signal 
applied at the amplifier input terminals. The amplifiers may be the left 
and right channels conventional stereo amplifiers, two mono amplifiers or 
any similar audio system components. Each amplifier 110, 120 includes 
positive and negative output terminals 116, 126, 117, 127. According to 
the present invention, the positive output terminal 116 of amplifier 110 
is connected to the positive input terminal 131 of speaker 130, and the 
positive output terminal 126 of amplifier 120 is connected to the negative 
input terminal 132 of speaker 130. The connections between the amplifiers 
and the speakers may be effected by a second cable (not shown), as 
described in FIGS. 2 and 4. 
With the connections described, and a balanced signal produced by the 
preamplifier 101, each amplifier 110, 120 will generate a signal based 
upon one component of a balanced signal and system ground; thus, the 
signals at the positive output terminals 116, 126 of the amplifiers 110, 
120 will form a balanced signal, and the advantages of a balanced signal 
are carried through to the speaker 130 output. 
FIG. 2 shows a two-channel configuration of an audio system in accordance 
with the present invention. The following description is of either channel 
of the audio system. The positive, negative and ground output terminals 
(not shown) of the preamplifier (or similar device) 101 are incorporated 
in an output connector (or connectors) 140. It should be noted that the 
connectors conventionally incorporate positive, negative and ground 
terminals. Persons of ordinary skill in the art will recognize that 
connectors generally may be designed in a variety of ways and may include 
one or more of the terminals that effect the electrical connections. 
A specialized first cable 160 effects the connection between the 
preamplifier 101 and the amplifiers (or similar devices) 110, 120. The 
cable has an input connector 150 at one end of the cable and two output 
connectors 165, 166 at the opposite end of the cable 160. The input 
connector 150 is suitable for connecting with the output connector 140. 
The conductors (not shown) comprising the cable 160 may be of any 
configuration suitable for audio cables including twisted pair, untwisted, 
multistrand wires or coaxial cable. The cable divides at a point 213, near 
the output connectors 165, 166 such that one output connector 166 may be 
connected to the input connector 168 of the amplifier 110, and the second 
output connector 165 may be connected to the input connector 167 of the 
amplifier 120. 
The two output connectors 165, 166 may be of any design suitable for 
connecting to the input connectors 167, 168 of the amplifiers 110, 120. As 
further shown in more detail in FIG. 3, the internal conductors of the 
cable are also divided at point 213 and are configured to implement the 
connections between the preamplifier 101 and the amplifiers 110, 120 shown 
in FIG. 1. 
Each of the amplifiers 110, 120 has an output connector 170, 172 associated 
with the positive output terminal and an output connector 175, 176 
associated with the negative output terminal all of which may be of any 
suitable design. A second cable 180, includes two input connectors 171, 
173 suitable for connecting with the output connectors 170, 172 of the 
amplifiers associated with each amplifier's positive terminals. The cable 
180 is divided such that its input connectors 171, 173 may connect to the 
output connectors 170, 172 of the amplifiers 110, 120. The conductors (not 
shown) comprising the cable 180 may be of any configuration suitable for 
audio cables including twisted pair, untwisted, multistrand wires or 
coaxial cable, and, as shown in more detail in FIG. 4, are configured in 
association with the input connectors 171, 173 and output connectors 190, 
192 to effect the connections shown in FIG. 1 between the amplifiers 110, 
120 and the speaker 130. The output connectors 190, 192 are designed to 
connect to the input connectors 191, 193 of speaker 130. 
FIG. 3 shows a schematic representation of cable 160 suitable for 
connecting the preamplifier components to the amplifiers 110, 120 in one 
channel according to the present invention. The input connector 150 (shown 
in FIG. 2) includes input terminals for positive 201, negative 202 and 
system ground 200. In certain audio applications, the equipment chassises 
are grounded separately from the circuits. In those applications, the 
input and output cable connectors would also include terminals for the 
chassis ground 230, 231, 232, in addition to those for the circuit ground 
200, 207, 209. Another common configuration ties the terminals (or their 
equivalent) for chassis ground 230, 231, 232 to the terminals for circuit 
ground 200, 220, 221, usually within the connectors, to eliminate the 
separate grounding in the system. 
Each of the input terminals is connected to an associated conductor 203, 
204, 205, 233. The conductor for chassis ground is often an external braid 
233 (shown schematically) on the cable. As stated above, the conductors 
203, 204, 205, 233 may be configured in any manner usual for audio cables, 
including twisted pair, untwisted, single or multistrand wires or coaxial 
cable. 
The conductors are grouped into a single cable package for some length of 
the cable, but the cable package is divided into two cable packages at a 
point 213 (also shown in FIG. 2), each containing at least two conductors. 
The conductor 204 associated with the positive input terminal 201, appears 
in one of the two packages and is connected to the positive terminal 207 
of the output connector 166 (shown in FIG. 2). The conductor 205 
associated with the negative input terminal appears in the other package 
and is connected to the positive terminal 209 of the second output 
connector 165 (shown in FIG. 2). 
The second conductor 203 in each of the two packages is circuit ground, and 
the conductor 203 is electrically connected to the negative output 
terminals 208, 210 and to the ground output terminals 220, 221 of each of 
the output connectors 165, 166 (shown in FIG. 2). If a separate chassis 
ground is used, the conductor associated with such chassis ground will be 
electrically connected to each of the chassis ground terminals 230, 231, 
232. Alternatively, if a single ground is used, as described above, the 
conductor for chassis ground 233 may be electrically connected to circuit 
ground, usually by tying each terminal for chassis ground 231, 232 to the 
connected terminals for circuit ground 221, 220 and negative input 208, 
210. 
In practice standard cable often includes a third conductor. Therefore, for 
manufacturing ease, each of the two packages may contain a conductor 240, 
241 that is connected to the negative input terminal 208, 210. These 
conductors 240, 241 are left unconnected near the point of division 213. 
As persons of ordinary skill in the art will appreciate, these conductors 
240, 241 may be eliminated or shortened without any effect on the cable 
function. 
FIG. 4 shows a schematic representation of a cable suitable for connecting 
the amplifier components to the speaker in one channel according to the 
present invention. The connector includes two input terminals 301, 302. As 
noted in FIG. 2, the connectors may be of a standard connector of any type 
generally used for audio cable applications and suitable for connecting to 
the positive output terminals of power amplifiers. Each of the input 
terminals is connected to an associated conductor 303, 304. The conductors 
303, 304 may be configured in any manner usual for audio cables, including 
twisted pair, untwisted, single or multistrand wires or coaxial cable. The 
two input terminals 301,302 must be configured to be able to connect to 
the positive output terminals of two amplifiers 110, 120 as described in 
connection with FIG. 2. Therefore, although the two conductors are 
preferably packaged together for most of the length of the cable 320, the 
conductors must be separable adjacent to where they are connected to the 
two input terminals 301, 302 identified as region 321, to allow for the 
connection to the amplifiers. For most applications a separation of 
approximately one foot is adequate. 
The conductor 304 associated with the first input terminal 302 of the cable 
is connected to output terminal 311 which is part of output connector 190 
(shown in FIG. 2) and is suitable for connecting to the positive input 
terminal of a speaker. The conductor 303 associated with the second input 
terminal 301 of the cable is connected to a second output terminal 309 
which is part of output connector 192 (shown in FIG. 2) and is suitable 
for connecting to the negative input of the speaker. 
The cables connecting the preamplifier and the power amplifiers and the 
power amplifiers and the speakers may incorporate noise suppression 
networks, filters or similar devices. For example, two such networks are 
described in U.S. Pat. Nos. 4,954,787 and in 5,142,252 (the "'252 
Patent"), which are incorporated by reference herein. Such networks are 
not necessary to achieve a balanced output in an audio system and the 
advantages thereof, however, if such networks are used, as would be 
evident to those of ordinary skill in the art, they should be configured 
so that the specific phase and amplitude relationship of the signals is 
maintained in the system. For example, essentially identical networks of 
the type shown in the '252 Patent can be used in each of the cables 160, 
180, and inductors can be placed in (or to affect) both the positive and 
negative conductors in each cable. Obviously, it is therefore important to 
have the values of all network components affecting one signal or channel 
to be very close to the values of the components affecting the other 
signal or channel. Thus, precision components, and/or component 
configurations in such networks are preferable. 
While preferred embodiments of the present invention are described above, 
it is contemplated that various modifications may be made thereto without 
departing from the spirit and scope of the present invention. For example, 
while the present invention is directed towards a high fidelity sound 
system, the benefits of the present invention may be realized anywhere 
high quality sound reproduction is desired, such as in a recording studio, 
a professional concert or theater sound reproduction system, or a modem 
home theater system. Accordingly, it is intended that the embodiments 
described be considered only as illustrative of the present invention and 
that the scope thereof should not be limited thereto but be determined by 
reference to the claims hereinafter provided and their equivalents.