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FEATURE
ABSOLUTE BEGINNERS GUIDE TO HOME CINEMA
HEAD
How to connect up a home cinema system
INTRO
It all looks so simple in the showroom, lots of shiny boxes,
all working seamlessly together. In the real world few home cinema systems are
ever planned, they evolve, as components are added or replaced, with little or
no thought to the problems of connectivity.
The connectors and cables used in an AV system can be just
as important as the components themselves. Using wrong the leads can adversely
affect both picture and sound quality, it could even mean you miss out
completely on stereo sound and surround-sound effects. We take a close look at
the various types of AV connectors, and how they’re used
COPY
1. TV to VCR
If your TV and video recorder both have SCART AV connectors
you should use them. It will give an immediate improvement in picture and sound
quality, compared with an aerial lead connection, as the signals have to pass
through fewer stages of processing. Audio information from the VCR, sent via
the aerial lead to the TV is in mono, so a SCART connection is essential in
order to get stereo sound from a hi-fi VCR. If the VCR has only one SCART
connector and it is being used to connect the machine to a satellite receiver,
say, then it is possible to use the video recorder’s stereo line audio output
sockets to connect it to the TV, using a SCART-to-phono lead. The TV will have
to rely on the aerial connection for the picture signal, and quality will
suffer slightly as a consequence. The TV will also have to be configured for an
external audio input. The aerial lead to the TV must still go via the VCR
otherwise it will not be able to record off-air broadcasts.
2. TV/VCR/Hi-fi Stereo Amp
If you have a stereo hi-fi VCR but only a mono TV, or an
older/ flaky stereo set, you can route the sound from the VCR through your
hi-fi system. You will also be able to hear TV programmes (live and recorded)
in stereo, assuming the VCR is a NICAM model. Ideally the VCR and TV should be
connected together using a SCART-to-SCART lead (type C or U), to carry the
vision signal; alternatively an aerial lead connection will suffice, though
picture quality will not be as good. The VCR and hi-fi will need to be fairly
close together, and the speakers placed a foot or so either side of the TV
screen. The next step is to connect the stereo audio output from the hi-fi VCR
(usually a pair of phono sockets) to the auxiliary input on the hi-fi
amplifier, using a stereo phono-to-phono lead. Some later models of hi-fi have
an auxiliary input labelled VCR or video. The auxiliary (or VCR) input should
be selected on the hi-fi, whilst the sound on the TV should be muted or turned
right down, so that it cannot be heard.
3. TV/VCR/Stereo Amp/DPL Processor
One of the quickest and simplest ways to upgrade to
multi-channel cinema surround-sound is to add a Dolby Pro-Logic (DPL) processor
to an AV system. Stand-alone processors contain the DPL decoder and two,
sometimes three audio amplifiers. These drive the two rear-effects speakers and
the centre-front dialogue speaker. The front right and left channels are
provided by the hi-fi. Some processors have multiple AV inputs, so they can be
used to switch between a number of source components, including a satellite
tuner, laserdisc or CD-i player. In order to extract the Dolby Surround
information the processor has to connect between the sound source (VCR etc.)
and the main hi-fi amplifier. This will require two stereo phono-to-phono
leads. The first one links the stereo line output from the VCR (or any other
source components) with the processor’s audio input. The second lead is used to connect the processor’s
front channel stereo line-output with the hi-fi amplifier’s auxiliary or VCR
input. The front stereo speakers can be left in place, either side of the TV
screen. The two rear-channel speakers are located behind, or to the side of the
listening position, whilst the centre-front dialogue speaker should be on top
of the TV, or as close to the screen as is practical.
4. TV/VCR/Integrated Amplifier
Integrated AV amplifiers, with built-in Dolby Pro-Logic
decoders, are normally very easy to install and set-up. Most of them have
several audio source inputs, so they can be used as switching centres for a
number of AV components, including one or more
VCRs, a satellite receiver and laserdisc player. The line audio output
from each source component connects to the amplifier’s line inputs by a stereo
phono-to-phono lead. AV amplifiers normally have five speaker outputs, two for
the main front stereo channels, two go to the rear effects speakers; the fifth
goes to the centre-front dialogue channel speaker, placed close to the TV
screen. In most cases the TV and VCR will be connected together using a
SCART-to-SCART lead, the TV sound is switched off or muted. Some AV amplifiers
have connections for video information as well. In most cases the video signal
simply passes in and out of the amplifier, without being affected in any way. A
handful of AV amps incorporate a video switcher, with additional outputs, so
the signal can be fed to a second TV, or a second VCR. A couple of models
superimpose on-screen graphics onto the video signal, showing mode or status
information.
5. Integrated Amplifier to five speakers (inc. active sub)
A growing number of AV amplifiers (with on-board DPL
decoders) have a separate sub-woofer output, carrying low-frequency or bass
sounds, that may not be fully resolved using ordinary hi-fi speakers. The
sub-woofer output is a line-level signal, which is too weak to drive a
loudspeaker directly, so it has be amplified in order to be heard. A separate
amplifier could be used, though the simplest approach is to use an ‘active’ sub
woofer, which has the amplifier built in to the cabinet. Sub woofers can usually be placed anywhere
in the listening area (low frequency bass sounds are not very directional), but
it will need to be placed within reach of a mains outlet. The connection
between the amplifier and ‘sub’ is usually a single phono-to-phono-lead. The
rest of the connections, between the AV amplifier, VCR and other source
components, and the TV are identical to those for a system with an integrated
AV amplifier.
6. Stereo amp & DPL decoder to five speakers
Virtually all stand-alone DPL processors have three
amplified outputs. Two of them are for the rear channel speakers (situated
behind the listening position), these carry the surround sound information and
special effects. The third output goes to a speaker placed on or close to the
TV, for the centre-front dialogue channel. Few DPL processors come with
speakers or cables but the requirements are normally quite modest as the power
levels are usually quite low, moreover the frequency bandwidth of the effects
and dialogue channel are fairly narrow. The main consideration with the speaker
cables is that they should be long enough. Reckon on between five to ten metres
for each speaker, depending on the size of the room, as the cables will have to
be routed out of the way, under rigs or carpets, or behind skirting boards and
furniture. In most cases it is not necessary to use expensive high performance
cable in this application. The VCR and TV should still be linked together by a
SCART-to-SCART lead, for the best picture; the sound on the TV should be turned
down. Some older DPL processors do not have an amplified centre-channel output,
in which case it may be possible to use the TV’s speaker by connecting the
processor to the TV’s audio input (assuming it has one).
7. DPL Amplifier to TV, VCR & Satellite receiver (or
LaserDisc CD-i etc.)
Connecting a satellite receiver to a system isn’t usually a
problem, provided it is a reasonably recent mid-market model, with two or three
SCART AV sockets. The SCART connection from the VCR to the TV is routed to one
of the SCARTs on the back of the satellite receiver, this will enable the VCR
to record satellite TV programmes in stereo. The aerial connection between the
TV and VCR remains in place, so the VCR can record terrestrial TV programmes as
well. A second SCART lead connects the satellite receiver’s AV output to the
TV, on some models it may be necessary to leave the satellite receiver switched
on when replaying tapes on the VCR. The stereo line audio outputs from the
satellite receiver and VCR both connect to the AV amplifier’s audio inputs by
stereo phono-to-phono leads. If the STV receiver doesn’t have enough SCART
sockets the picture signal will have to be carried to the TV by
‘daisy-chaining’ the aerial lead. Unless the TV or VCR have two or more SCART
sockets any additional components will involve making some kind of compromise
over picture or sound quality, or both. Alternatively the AV outputs can be
routed to the TV by a SCART switch or splitter box
8. Speakers -- passive sub wired in with rears
Passive or unamplified sub-woofers are designed to handle
the low-frequency notes that would otherwise be directed to the front speakers,
and almost certainly lost due to the poor bass characteristics of most
mid-range and purpose-designed AV speakers. A passive sub-woofer connects
between the AV amplifier and the front right and left channel speakers. Inside
the sub-woofer there is a crossover or filter network, that separates out the
bass frequencies, before what remains of the signal is passed on to the front channel speakers. The
interconnection are very simple: the right and left channel speaker outputs
from the main amplifier go to a set of ‘input’ terminals on the sub-woofer; a
second set of ‘output’ terminals connect the sub-woofer to the front speakers.
It is important that the sub-woofer and front channel speakers are matched
otherwise the sub may not perform correctly. Unlike an active sub-woofer,
passive ‘subs’ may need careful placement, especially if there is any higher
frequency leakage, which may confuse the surround-sound effect. It is usually
worth using a decent-quality heavy-duty cable for the front channel speakers
and sub.
BOXOUT 1
Speaker Wiring
There are at least four different cable connection systems
used on amplifiers and loudspeakers. Specialised plugs and sockets, (normally
2-pin DIN or jack-type connectors) are favoured by manufacturers of low-end
mini and midi systems as they’re virtually idiot-proof. Simple spring
terminals, that clamp the bare ends of the speaker cables are widely used on
mid-range amplifiers and speakers. More expensive and higher performance
components use binding posts or screw terminals, that tightly grips the bare
cable, which passes through a hole in the centre of the post. Alternatively,
cables can be terminated with ‘banana’ plugs, which fit into 4mm sockets in the
pillars of most binding posts
BOXOUT 2
Speaker polarity
Loudspeakers are polarity-sensitive, which basically means
they must be connected the right way round. If they’re not it can result in
peculiar phasing effects, caused by the cone in one speaker travelling in the
opposite direction to the one in the other speaker. All speaker leads and
terminals are clearly marked or colour-coded, so that there’s no possibility of
getting the wires mixed up. In other words the lead connected to the black or
negative terminal on the amplifier must go to the correspondingly marked
terminal on the speaker, and so on. It’s also worth mentioning that some
high-end speaker cables are ‘directional’, and only one (marked) end should
connected to the amplifier.
BOXOUT 3
DPL Channel Balance
All Dolby Pro Logic decoders, whether they’re stand-alone
components, or built inside amplifiers, or televisions etc., must have some
kind of channel balance facility. In most instances it consists of a sequenced
white or pink noise generator that feeds a whooshing sound to each channel in
turn. The objective is to adjust the amplifier’s volume and balance controls,
so that the channels sound equally loud from the main seating position. When
playing Dolby encoded material the rear effects channel will actually sound
quieter than the front channels, this is quite deliberate, and prevents the
rear channel from dominating and distracting the viewer’s attention from the
screen.
BOXOUT 4
The Right Lead
The coaxial aerial leads used to connect video recorders to
televisions are a throwback to the days when TVs didn’t have AV sockets.
Off-tape picture and sound information from the VCR is re-processed and piped
into the aerial feed, so that the TV treats it like an extra TV station. VCRs
do not have the facility to encode stereo audio, so even if the TV is a stereo
model, the sound coming out of the TV speakers will be mono.
Nowadays most AV products (TVs VCRs, satellite receivers,
laserdisc players etc.) have SCART AV connectors. The 21-pin plug and socket
system carries a variety of audio, video and control signals. There are several
configurations but the commonest are type-C or ‘9-pin’ leads, which have all
the audio and video pins wired together, and type-U or universal leads, that
have all 21 pins connected. The latter should be used for hook-ups between
Super VHS video recorders and S-Video compatible TVs.
Phono (aka RCA and ‘Cinch’) connectors are mainly used for
carrying audio and composite video information between items of AV equipment.
Composite video signals contain a mixture of complex signals, which can
interact with each other, resulting in pattering and cross-colour effects.
High-performance video systems use S-Video connections, where the brightness
(luminance or Y component) and colour information (chrominance or C component)
signals are carried separately using 4-pin min DIN or specially configured
SCART connectors.
BOXOUT 5
Five Cable & Lead Top Tips
* Get the right lead for the job, don’t try and make do with
adaptors or converters, they’re a frequent cause of failure
* Cheap leads and connectors are a waste of money, they’re
less reliable and may add extra noise to the video and audio signals
* The converse is also true, super-expensive speaker cables
are really only of benefit on high-end audio systems; AV equipment and software
tends to be far less critical
* Always treat plugs and sockets with care, excess pressure,
or repeated plugging and unplugging leads to intermittancy and faults
* Gold-plated connectors give a better electrical contract
and will not corrode; they’re worth paying a little extra for if your equipment
is used in a humid atmosphere
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R. Maybury 1995 2410
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