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BearBoy

Switch for Coaxial Digital Cables

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Trying to solve something of a cabling conundrum and wondered if anyone here might be able to offer any advice.

Is there any reason a switch like this: https://www.amazon.co.uk/HQ-3-Way-Stereo-Input-Control/dp/B000I8OOS8/ref=sr_1_1?s=electronics&ie=UTF8&qid=1476379763&sr=1-1&keywords=rca+switch+box

couldn't be used with coaxial digital cables?

i.e. I would like to connect multiple sources to a single coaxial digital input on a MiniDisc deck and switch between them.

Obviously this switch is stereo but if I just used the red connections would it be likely to work?

I have seen plenty of optical switches but cannot find anything for coaxial.

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21 hours ago, BearBoy said:

If I see correctly, this unit is switching analogue stereo audio signals on RCA connectors. While the physical connector is the same (except for "colour code") as the one used for SPDIF, there is a significant difference in bandwidth: the digital signal is in the MHz range, while the audio is in the 20+ kHz range.

Having said that, if the inside is just a pure selector switch without any sophisticated electronics, it might still work, though at those high frequencies proper noise filtering is another issue.

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11 hours ago, PhilippeC said:

Coaxial has a stereo signal, if you plug on a RCA, I suppose it will become mono

Not the SPDIF digital signal, that can be stereo or even multichannel on one single line.

 

For coaxial and RCA:

"Coaxial" is a generic term, describing cables with circular cross section, a core wire in the center, a shielding net around, and an electrical isolation between. "RCA" is a connector (for coaxial wire), not only for analogue audio, but also for for other signals, like SPDIF, composit video, component video, or even for loudspeakers' outputs, etc. There are other type of coaxial connectors too, like "BNC" for example.

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11 hours ago, BearBoy said:

I have seen plenty of optical switches but cannot find anything for coaxial.

There are many of them, though mostly combined with optical TOSLINK, like this one for example.

It is not very difficult to build one either. If you want something that is not passing the few MHz digital signal through the (somewhat unreliable) mechanical contact of a switch, you can use a couple of simple, standard CMOS IC-s.

 

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Thanks for the replies and the link.

Unfortunately the switch in that link, like many of the others ones I've found, doesn't have a coaxial digital output, just optical and analogue.

I've found this one on eBay that looks perfect but is significantly more expensive (it costs more than I've spent on most of my MD kit): http://www.ebay.co.uk/itm/TOSLink-Coaxial-Digital-Auto-Switcher-Switch-SPDIF-Audio-Authority-1177A-1-GSP-/361415723423?hash=item54260e499f:g:8V0AAOSwAYtWK6w6

I've also found this one, which would probably suffice but only has two inputs (and I would ideally like three): http://www.ebay.co.uk/itm/Coaxial-Coax-SPDIF-Bi-Directional-Switch-Box-Converter-Selector-2-to-1-or-1-to-2-/371627677571?hash=item5686bc5783:g:cWMAAOSwdV1XN3Gj

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4 hours ago, NGY said:

It is not very difficult to build one either. If you want something that is not passing the few MHz digital signal through the (somewhat unreliable) mechanical contact of a switch, you can use a couple of simple, standard CMOS IC-s.

I think you might be significantly over estimating my electronics skills ;)

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1 hour ago, BearBoy said:

Unfortunately the switch in that link, like many of the others ones I've found, doesn't have a coaxial digital output, just optical and analogue.

That's right, I overlooked that part.

(SPDIF optical to coax conversion is very, very simple though, and requires a couple of passive components only - I mean, if you do it before the TOSLINK transmitter. In other words, a unit with optical out can be modded for having a coax output. Same circuitry exists in many Sony decks.)

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6 hours ago, BearBoy said:

I've also found this one, which would probably suffice but only has two inputs (and I would ideally like three): http://www.ebay.co.uk/itm/Coaxial-Coax-SPDIF-Bi-Directional-Switch-Box-Converter-Selector-2-to-1-or-1-to-2-/371627677571?hash=item5686bc5783:g:cWMAAOSwdV1XN3Gj

I know it may sound weird, but you can cascade two of these into a third one, and you can control four inputs. But that would probably worsen your cable problems.

 

 

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59 minutes ago, BearBoy said:

I think you might be significantly over estimating my electronics skills ;)

I am sorry for that.

How quick would you need such a switch? As I mentioned in another topic, I am in the progress of making a selector switch - originally intended for optical only (and made from recycled Sony md deck parts), but no big deal to add coax too. When I am done, and if it is something I can replicate from ~15 bucks worth of parts, I can build a second one.

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19 minutes ago, NGY said:

I know it may sound weird, but you can cascade two of these into a third one, and you can control four inputs. But that probably worsen your cable problems.

I had considered that but, as you say, it wouldn't really help with my overall aim of a simple/neat cabling set up. The switches also require power (they seem to be USB powered) so I think I'd end with a right mess of cables :)

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32 minutes ago, NGY said:

I am sorry for that.

How quick would you need such a switch? As I mentioned in another topic, I am in the progress of making a selector switch originally intended for optical only (and made from recycled Sony md deck parts) -, but no big deal to add coax too. When I am done, and if it is something I can replicate from ~15 bucks worth of parts, I can build a second one.

Absolutely no need to apologise. I am endlessly impressed with the technical skills of some of the people on here.

Thank you for your very kind offer. I have been having another think about how all my various devices can be connected and I think I can get away with a 2 way switch for now (as long as I don't buy any more decks.....)

If that changes though I would certainly be interested in a switch with more inputs/outputs so might get back to you on that. Thanks again.

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My relatively limited experience with coax (most of my digital cabling is TOSlink) is that it's noise prone. Also, unlike TOSlink, when you connect two devices with a coax cable, there is at least the **possibility** of a signal ground loop which may interfere with the high frequency data being transmitted,

The only relevant case (for me) was right when I started in this digital sound game, I purchased from an astute individual in Europe (no it was many years ago and it most definitely wasn't NGY) a magic connector/converter that did clever things with the output from a cd drive, back before the software companies figured out how to rip without even using the digital output. Its biggest fault was that if the connectors were even slightly loose you got annoying glitches and bursts in the sound. I always assumed it was due to the less-than-perfect nature of the cabling (gold connectors would be ideal but I simply couldn't afford them then).

Introducing a mechanical A-B switch of some kind is subject to this kind of possibility INTERNALLY. That's what I would worry about.

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Well, I ordered the two input switcher I linked to above (but from Amazon rather than eBay) and it arrived today. Seems to work fine so far. 

Also, in case anyone was interested, it works without the power connected, although the input select light doesn't work. Should cut down on the wires...

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On 2016. október 15. at 9:49 PM, BearBoy said:

it works without the power connected, although the input select light doesn't work.

I would love to see, what's inside. No intention to disappoint you, but if it is a bidirectional device that works without power, then I suspect it is just a mechanical switch. Maybe a few resistors to keep the box at 75 Ohm, and a couple of capacitors for basic noise filtering, probably a high-pass filter, if the designer paid attention to such details.

Would you mind risking your warranty by removing the sticker, to peep inside? I mean, if it is not a big trouble (de/recabling again). My own circuitry schematic for a 3-to-1 selector is just waiting for some spare time to make the PCB and solder a prototype. Would be interesting to see others' s solutions.

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I opened it up and took a photo for you. As far as I can see there are no electrical components on the underside of the circuit board so I'm guessing that it is nothing more than a mechanical switch with LEDs to indicate which path is selected.

 

Digital Switch - Copy.JPG

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Thanks for taking the trouble.

In the lights of this, my version looks a bit overcomplicated :-) . I will digitalize the schematics and post it here in an enjoyable format, for those with some electronics vein who want to build their own. But prior to that I want to do the test ride, to prove the concept.

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No problem. I am sure the switch you are working on will be a much more refined design. If it doesn't look too tricky I might try making one myself so I could have three inputs.

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