HOME ENTERTAINMENT 95

 BootLog.co.uk

HomeSoftwareArchiveTop TipsGlossaryOther Stuff

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

 

---end---

Ó R. Maybury 1995 2410

 

[Home][Software][Archive][Top Tips][Glossary][Other Stuff]


Copyright (c) 2005 Rick Maybury Ltd.

admin@rickmaybury.com