3.5mm jack plugs and 7:1 audio

[I think I'm answering most of my questions as I work through the description, but would still like to check my understanding.]

I'm trying to put together a home audio system based around a Home Theatre PC (HTPC).

I'm only planning to use 5:1 (well, 5:0 because the speaker system doesn't have a sub) and I'm looking at the diagram for the sound card.

This has wiring options for various configurations from 2:1 to 7:1.

Now as far as I know 3.5mm jack plugs have a minimum of 2 connectors - signal and ground for mono. If you go to stereo you get 3 connectors for left signal, right signal, and ground.

If you go to a connection with a microphone you get yet another connector.

[Looking at Google these are being referred to as conductors.]

With this sound card (Soundblaster Audigy 5/RX) there are three line out sockets to serve all the speaker channels (8 channels for 7:1).

For example Line Out 3 can support centre, sub, and side left.

So, the thing that is causing me mental indigestion; where you can support up to 3 channels I presume you need a four conductor plug. However what plug do you use if you are on 5:1 and want only centre?

Is there some scheme for connecting 3.5mm sockets together where one end supports more connections than the other?

For a similar example, on the smaller 2.5mm mobile phone sockets you can use stereo headphones (3 conductor) or headphones and a microphone (4 conductor). How do you cope with both plugs?

Anyway.

For my set up the audio output from the card is plugging into the rear of an old AV amplifier which has phono connectors. I am assuming that for the front speakers I need a 3.5mm stereo jack plug to two phono plugs. I can see these on t'Internet easily.

For the other connectors, I assume I need a 4 conductor 3.5mm jack to 3 separate phonos (for example side left, centre, sub). All the ones I am seeing are marked "left, right, video". That is, old style pre SCART audio/ video cables. Are these O.K. for my set up or is there a magic search phrase I haven't yet located?

Cheers

Dave R

Reply to
David
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should be just fine

Reply to
The Natural Philosopher

Wikipedia calls them conductors but I call them poles.

There are some conventions about how the poles are used which gets followed for compatibility (eg headphone sockets and heaphone plugs). However Creative doesn't follow this "headphone" convention.

Creative sends the signals for the 2 front channels through one 3 pole jack.

It sends the signals for the 2 rear channels through a second 3 pole jack.

Finally it sends the signals for the centre front channel and also the special effects channel (which you don't want) through a third

3 pole jack.

These are ordinary 3 pole stereo jacks. You might have some of these leads just lying around.

See page 22 here:

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4 pole jacks would work but are unnecessary.

If that old AV amp of yours supports optical then it makes everything simpler and is also more reliable.

Personally I really like the special effects channel and wouldn't be without it.

Reply to
pamela

Is that the channel with the cunning stunts on it?>

Reply to
The Natural Philosopher

Americans call the poles tip ring and sleeve. They even still call the conductors in a telephone wire pair T&R because that's where they were connected in a manual telephone exchange.

Reply to
Graham.

Is that a policeman's truncheon or are you ... etc ?

Reply to
pamela

The standard GPO plug - in the days of manual exchanges etc where you saw the operator plug up a call - and also used for broadcast jackfields, was called TRS. I assumed this was a UK device - although it might have originated in the US.

Reply to
Dave Plowman (News)

Indeed the only issues I've found with sound cards on board or otherwise has been weird shushing noises when discs are accessed or lots of memory shoving about goes on. Iyt seems this is either due to the interference radiating to the audio or its on the power lines on theh PC, so I do sometimes wonder why somebody does not address this problem. Even a usb box seems to get it on the playback sockets. Brian

Reply to
Brian Gaff

Think it depends on the quality of the sound card. I bought one used at a BBC auction - ex Bush house - that has balanced inputs and outputs, as well as unbalanced. That is as quiet as you'd wish. But IIRC, cost about

300 quid new.

Had a similar problem with an expensive Samsung TV. As is common these days, no analogue output specifically for connection to an external amp, so used the headphone socket. That had low level noise on it too. So had to get a toslink to phono adaptor which is clean.

Reply to
Dave Plowman (News)

The link you provide is the one I was using to conclude that "4 pole" jacks were required - that is, tip, two rings and a sleeve.

Look, for example, at Page 15 which shows a jack plug foe Line Out 3 and 3 RCA plugs to go into the AV equipment.

From this example, line out 3 carries sub/centre/side L which (as far as I can see) requires 3 poles, one for each channel, plus a common ground/ earth making 4 poles in all.

So I would expect a 3.5mm four pole jack and 3 RCA plugs; one for each signal channel and with ground/earth shared between the 3 * RCA.

Four poles to three RCA is a common very old video standard - left audio, right audio, composite video. These cables are dirt cheap. My main concern is if the electrical characteristics of the yellow 75 ohm video cable (yellow) are significantly different from the two audio cables (red and white).

Cheers

Dave r

Reply to
David

Just to add the following link:

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which contains a nice colour picture of the cable I require.

I have raised a support query to ask where I can buy one since they don't seem to be for sale in the store.

We shall see.

The feeling I am getting is that analogue is so last century and everything is digital now.

However I am trying to avoid using the on-board DAC for the AV amp because I am planning to connect the optical digital connection to the stereo amp to use the on board DAC there for playing music.

Cheers

Dave R

Reply to
David

Almost certainly not.

Indeed at that length I would doubt that any special effort to make the

75 ohm one '75 ohm' would be undertaken.

reflections would be so short in time as to be unnoticeable.

Reply to
The Natural Philosopher

Eh? A cable which can handle a high video bandwidth isn't going to have any problems with audio. And unbalanced audio is generally low impedance out, high in. So the typical cable impedance is neither here nor there.

Reply to
Dave Plowman (News)

Thanks.

Possibly go for about 1 metre in length to allow some flexibility in pulling out shelves to get at the back of the kit.

Is any significant shielding required?

Or will the "cheap as chips" cables be fine?

Lot of A/C power and other signal cables down the back of the stack.

Cheers

Dave R

Reply to
David

Phono cables are generally co-ax anyway.

Always best practice to keep signal and power cables separated. If they must cross, do so at right angles.

Reply to
Dave Plowman (News)

I've always used short thin audio phono leads for component interconnects from DVD players with no adverse affects.

Reply to
Graham.

Yes that's a 4 pole jack. It means there are three signal paths (plus the earth) and I imagine that is for either 2.1 or three front speakers. That isn't going to give you the 5.0 sound you want.

Does your AV amp expect jack or RCA phono plugs?

Reply to
pamela

formatting link

In that diagram I see 8 RCA phone plugs and that means 8 separate signal paths. Perhaps that diagram is for 7.1 speakers.

However you want a diagram for 5.1. (5.0 and disregard the .1 signal).

Reply to
pamela

I used to neatly coil my main power leads and then secure the coils with a cable tie. Would 5 or 6 turns be enough to cause interference?

Just to be safe, I'm now not so neat when coiling main cable.

Reply to
pamela

The electrons will get dizzy if you do that.

You could do half coiled one way then half the other :-)

Reply to
Clive George

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