Audio switching box...

[kaeyas]

Hi,

I have a very limited knowledge of electronics, I'm more of a software and computers person. However, I have recently decided to try and undertake a personal project, but I'm trying to acquire help with it.

At the moment i watch dvd's through my PC and have a surround sound system that connects to it through a sound card that has two 3.5mm stereo outputs (one for FRONT and one for REAR). There are four speakers, two front and two rear, and a subwoofer (if that helps).

Soon I will hopefully be acquiring a new external dvd player that will connect to my tv so i can watch them on that. The player will have four audio outputs, L&R front and L&R rear. These outputs are standard Phono outputs, and therefore cannot use the speaker system I already have.

So here's the project I would like to undertake, I would like to have a box that has two types of input. One set of inputs (four phono sockets) which the dvd player can connect to, and another set of inputs (two 3.5mm stereo sockets) which the PC can connect to. Then I would like one set of outputs (two 3.5mm stereo sockets) to connect the speaker system to. A visual display on the front, perhaps digital could be good to show that there is actually an input source and which one it is, but LED's can also be sufficient.

I have the visual design that i can create in my head, but as for the electronics, itz been 6years since I did gcse electronics at school, so I'm a little rusty. If anyone who reads this can help with circuit diagrams and layouts, or point me in the right direction of what to use or where to get information, It would be very appreciated.

Thank you!

 

[ab0tj]

You could always run the audio of the DVD player to the Line In on the computer.

 

[Nigel Goodwin]

I'm rather confused about your DVD player, it sounds very strange having 4 phono outputs? - they usually have 6 phonos, for Dolby 5.1, left, right, centre, rear left, rear right, and sub-woofer.

What you need is an AV 5.1 amplifier, if your DVD hasn't got the six outputs required, you would need one with an in-built Dolby 5.1 decoder, and connect your DVD via an optical or coaxial digital lead.

You will also need some proper speakers, computer ones are rubbish, any halfway decent amplifier will blow them to pieces - their power specifications are an incredible work of fiction!. I've recently seen PC speakers advertised as '1000W', then in little writing '20W RMS'. These would be exceptionally high power ones, most only use 2W or 3W drivers.

 

[kaeyas]

The dvd player has just four phono outputs for audio, but six in total if you include the two video outputs. There is also an s-video output, a coaxial output and an optical output.

Hope that clears things up.

 

[grrr_arrghh]

if you will only ever want to listen to one source (DVD or computer) at a time, it can simply be done using a multi-way switch (to change which input you are listening to. The display could be in the form of two LED level meters such **broken link removed**

on a phono, jacket is ground, pin is signal. Red is right, white is left.

on a 3.5mm stereo socket, tip is left, the bit in the middle is right, the long bit by the plastic housing is ground.

to connect two phonos to a 3.5mm socket, connect the left and right signals on the phono to the left and right on the 3.5mm, and connect the grounds together (in this instance all of these would probably be via a switch)

However, if you want to listen to both your DVD and computer at the same time, then listen to nigel, as you will need some kind of amlyfier/mixer. (also, his point about computer speaker quality is worth thinking carefully about)

errmm, TWO video outputs? (usually phonos come in threes - left audio, right audio and video - white, red and yellow). Are you sure that your player doesn't just have two sets of outputs, each with stereo sound, not surround?

also, maybe you could connect the optical output to an optical input on you computer? only that it would be difficult to connect 4 point surround to standard line in on a computer (line in is usually just stereo), but it can be done (i'll explain more if you need me to)

(in summary) If you do only want to listen to one thing at a time, then make a simple switch as described in the first paragraph - it will be much cheaper than an amplyfier.

Just some ideas.

Tim

 

[Nigel Goodwin]

The dvd player has just four phono outputs for audio, but six in total if you include the two video outputs. There is also an s-video output, a coaxial output and an optical output.

Hope that clears things up.

Not really, I don't see what the four outputs could be for?. DVD's are generally recorded using Dolby 5.1, so a surround sound DVD player needs six audio outputs - as already mentioned by grrr_arrghh, what colour are the sockets? - and also what are they labelled?.

It sounds like you would be better off with an external Dolby 5.1 amplifier/decoder, and connect from the optical or coaxial ouputs.

 

[kaeyas]

Thanks for the advice guys, I might have to call upon my dad who's an ex-electronics expert, to help me construct it. The idea is only to listen to one thing at a time, so either the dvd player or the PC.

Itz a weird dvd player (it is made by alba), but itz 2nd hand and im thinking of getting a different one, which has the full 5.1 outputs. Would it be possible to have a digital coaxial input from the dvd player, and then an analogue converter that can output to the speakers. I know pc speakers are considered poor, but these ones are designed for both pc and home cineama.

If you're interested I've currently got a Logitech Z-560 THX Enhanced speaker system. There is a massive subwoofer which really kicks out some proper bass, and then four satellites of modest size. It connects to the output source via two 3.5mm plugs, one for front and one for rear.

 

[Nigel Goodwin]

Itz a weird dvd player (it is made by alba), but itz 2nd hand and im thinking of getting a different one, which has the full 5.1 outputs. Would it be possible to have a digital coaxial input from the dvd player, and then an analogue converter that can output to the speakers. I know pc speakers are considered poor, but these ones are designed for both pc and home cineama.

According to the spec at Logitech there's no mention of them being designed for other than computers - where are the amplifiers mounted?, inside the sub-woofer?.

A Dolby 5.1 AV amplifier should take the digital output from the DVD player and convert it into outputs for six speakers - also providing all the adjustments required, including individual levels for each speaker and delay timing to compensate for the listeners distance from the speakers.

If you have direct connections to each speaker (without any amplifiers in circuit) you could probably connect your existing speakers (plus an extra one) to such an AV amplifier. You could also probably connect your computer to the input of the amplifier as well.

If you're interested I've currently got a Logitech Z-560 THX Enhanced speaker system. There is a massive subwoofer which really kicks out some proper bass, and then four satellites of modest size. It connects to the output source via two 3.5mm plugs, one for front and one for rear.

I've had a look at the spec on them, they don't seem bad as computer speakers go, but you have the problem of no centre speaker - generally considered more important than the rears for Dolby 5.1. This is probably because they appear to be designed for computer use for THX, which is an older surround system.

 

[kaeyas]

Ok then, well it sounds like a direct connection would be best. I can play around with displays and indicators in the design.
Thanks 4 ur help guys, I shall let u know how it goes. If you have any more ideas then please let me know.

 

[grrr_arrghh]

just spotted this:

**broken link removed**

dunno if it would be any use, but its quite cheap.

Tim

 

[kaeyas]

Thanks, it looks rather good. I'll have a more in-depth look at it.