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I have a mac mini with 3.5mm audio out which I want to connect to an amplifier which is in another room, 20 metres away - the speakers are cabled back into the classroom. As well as a typical 3.5mm jack, it is also optical out which supports a "toslink mini-plug adapter", whatever that is. Given the distance, would I be better looking for a optical cable, an rca cable splitter from the classroom, 3.5mm cable which uses a splitter at the amplifier or something else? I am playing video, so audio latency is also an issue.

Amplifier connections

  • Deleted my answer as it isn't relevant at 20 meters instead of feet and would potentially have latency issues. I also updated the question to include the fact it needs to be a low latency solution. – AJ Henderson Jun 04 '13 at 12:48

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Your consumer grade optical link (the mentioned TosLink is Toshiba's name for a consumer standard) has a technical limit of 10 meters. It has been reported as being useable at up to 30 meters, but quality may suffer.

For best quality, what you probably want to do is go to a balanced format for the run. I don't know what you have available at the amplifier, but if it has the ability to take XLR (a circle with 3 holes in it) inputs, you could use a device called a direct box to switch the unbalanced output of the computer in to a balanced XLR cable which could safely make the 20 meter run.

If not, you might be able to make the run using a shielded 1/4 inch or even 1/8 inch cable since it is a somewhat powered signal, but it's going to depend a lot on the level of shielding and the amount of electrical interference in the area.

It might also be possible to use a direct box on one end and then use a balanced to unbalanced adapter on the other end, but I'm not sure what the performance implications of this would be as I've never personally tried it. I'm not even sure it would work correctly without a powered device on one end.

AJ Henderson
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  • Thanks for the very informative answer. The amp does have xlr so this looks like your solution might work great. Would this be what I am looking for? http://www.amazon.co.uk/Behringer-DI20-Ultra-DI-Channel-Splitter/dp/B000CCSWQA/ref=sr_1_2?ie=UTF8&qid=1370352330&sr=8-2&keywords=direct+box –  Jun 04 '13 at 13:26
  • @Mark - you could use something like that, though the active design means you need to either be able to supply phantom power from the amplifier rack or will need batteries. Phantom power is sometimes marked as a "+48v" button. If it doesn't have phantom power, you can use a passive DI like this. Keep in mind that XLR cables are also mono, so if you want to preserve stereo, you need to split the audio and go through two channels. – AJ Henderson Jun 04 '13 at 13:32
  • Passive sounds great as the amp doesn't seem to have phantom power. I've added an image of the amplifier, more info is found here: http://www.dasaudio.com/wp-content/uploads/documentos/documentos_d/manuales/ps/um_ps_01.pdf –  Jun 04 '13 at 13:40
  • @mark - is there any other signal processing in the rack? It's possible they are going directly in to the amplifier, but it is typical to have some signal processing prior to the amplifier in many setups. If you are able to take a picture of the entire rack it might help more unless the amp is the only thing there. – AJ Henderson Jun 04 '13 at 13:46
  • I only have the amplifier. Is that a bad thing? –  Jun 04 '13 at 13:53
  • @mark - not necessarily, but it lacks certain elements that are generally helpful for increasing quality and protecting equipment. Typically a 31 band EQ is used to fine tune the output to the room and it's also fairly typical in stand alone setups to put a limiter or compressor in line to protect the amp from clipping and overloads, but neither is absolutely critical. There are also some other signal processing devices that can sometimes be put in a rack to deal with particular situations. – AJ Henderson Jun 04 '13 at 14:43
  • Thanks for the advice. I think I'm going to go with a passive DI. If you have any advice on one which isn't too expensive I'd appreciate it. These are only for classrooms so nothing complicated really. –  Jun 05 '13 at 08:57
  • @mark - the one I linked is the cheapest one I have direct experience with though you can probably look at reviews to find one that would meet your needs. You might also be able to find an Active DI that can be plugged in that might be cheaper. – AJ Henderson Jun 05 '13 at 13:22