• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required as is 20 years of participation in forums (not all true). There are daily reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

Silly question, how to merge two coaxial inputs (assuming that one arbitrarly one shall be inactive) ?

Yasser 06

Member
Joined
Dec 4, 2020
Messages
68
Likes
9
Well a coax just carries a digital signal, so i believe that you just get two cables, so indeed its just like a rca but the cable is usually shielded.

So assuming that one have 2 coax inputs that are not active at the same time and only one coax input one may try to use the following elementary solution :
https://www.amazon.com/Monoprice-Digital-Coaxial-Splitter-Adapter/dp/B003L1AGVS#customerReviews
That one if more a splitter, so imagine it with male replacing female and vice-versa (or add 2 male -> female and one female -> male adaptors).

One could as well cut the coax connector merge the 4 wires two by two and insert them into a coax connector.

It should work as long as only one input is active, but if by mistake both are active this could lead to troubles since the amperage at the DAC input will then be twice what it should be , and even when one unit is active and the other plugged but inactive we shall get a potential difference at the output of the inactive unit, i wonder if this could damage it.

Someone post a merger/switch but it cost like 150 dollars if you add the coax option and it is overkill since you get then a switch operating 4 spif and 3 coax with 1 optical out and 1 coax out.

So any cheap and elementary slution is welcome.
 

DVDdoug

Addicted to Fun and Learning
Joined
May 27, 2021
Messages
867
Likes
1,038
That one if more a splitter, so imagine it with male replacing female and vice-versa (or add 2 male -> female and one female -> male adaptors).
The "good news" is you can find these things in almost any configuration or you can get adapters or cables with a male or female on both ends to "assemble" anything you want.


The bad news is you're not supposed to connect two (or more) outputs together. The output generally has a lower impedance and connecting one output to the other can kill (or greatly reduce) the signal. With regular audio signals we normally use a mixer (even if only one input is active at a time).

It generally is OK to use these things as "splitters" and connect two inputs together, although it could be a problem with these higher frequency 75-Ohm connections.

since the amperage at the DAC input will then be twice what it should be , and even when one unit is active and the other plugged but inactive we shall get a potential difference at the output of the inactive unit, i wonder if this could damage it.
Much-much more than twice but it's unlikely that you'll physically/permanently damage anything.
 
OP
Y

Yasser 06

Member
Joined
Dec 4, 2020
Messages
68
Likes
9
The "good news" is you can find these things in almost any configuration or you can get adapters or cables with a male or female on both ends to "assemble" anything you want.


The bad news is you're not supposed to connect two (or more) outputs together. The output generally has a lower impedance and connecting one output to the other can kill (or greatly reduce) the signal. With regular audio signals we normally use a mixer (even if only one input is active at a time).

It generally is OK to use these things as "splitters" and connect two inputs together, although it could be a problem with these higher frequency 75-Ohm connections.

Much-much more than twice but it's unlikely that you'll physically/permanently damage anything.


Do you know any passive mixer ? ie a Y like in the connector i posted but with a moving part that will connect the bottom bar of the Y exclusively to one of the top bars.
 

solderdude

Grand Contributor
Joined
Jul 21, 2018
Messages
11,410
Likes
25,310
Location
The Neitherlands
It's just a switch.
You can just as easily use a switch for RCA composite video.
Chances are any audio switch will also work well.
 
OP
Y

Yasser 06

Member
Joined
Dec 4, 2020
Messages
68
Likes
9
It's just a switch.
You can just as easily use a switch for RCA composite video.
Chances are any audio switch will also work well.
Well it is just a pair of electric wires with shielding, like one voice of RCA. But the connector is a bit different but it seems compatible.

I wonder why they use slightly different connectors, there must be a reason.

So you are probably right a simple rac switch may work, but i will only use half of it since all the voices go through a unique digital signal.
 

solderdude

Grand Contributor
Joined
Jul 21, 2018
Messages
11,410
Likes
25,310
Location
The Neitherlands
RCA for video and audio are the same AFAIK.
For video they just use the color yellow.
 

charleski

Addicted to Fun and Learning
Joined
Dec 15, 2019
Messages
640
Likes
1,230
Location
Manchester UK
The output generally has a lower impedance and connecting one output to the other can kill (or greatly reduce) the signal.
S/PDIF over coax cable uses a matched transmission line. The output impedance is 75ohm, the cable impedance is 75ohm, and the receiver impedance is 75ohm (IEC60958-3 2003 pgs 16-18). So the problem with just wiring two receivers together is that the transmitter sees an effective receiver impedance of half the standard, and you'll get signal reflections from the impedance mismatch. You could probably do it if you incorporated a couple of small coupling transformers to keep the impedance constant.
 

maverickronin

Major Contributor
Forum Donor
Joined
Jul 19, 2018
Messages
2,249
Likes
2,839
Location
Midwest, USA
Despite the fact that the specification calls for 75 ohm cable and termination, coax S/PDIF is very tolerant of all kinds of differences.

A simple "old fashioned" L/R/Composite video switcher should work just fine. I use one to switch several coax S/PDIF inputs into my RME ADI-2 DAC.
 
OP
Y

Yasser 06

Member
Joined
Dec 4, 2020
Messages
68
Likes
9
Despite the fact that the specification calls for 75 ohm cable and termination, coax S/PDIF is very tolerant of all kinds of differences.

A simple "old fashioned" L/R/Composite video switcher should work just fine. I use one to switch several coax S/PDIF inputs into my RME ADI-2 DAC.
great news.

Btw i don t get it, 30 year ago when i sutdied basic phyics (i went to math after) impedance and resitance was approximately linear in the length.
So if my switch is very short it should have low impedance and resistance -- simply by continuity and linearity --
so in a way if you have a 95% good connection and 5% of the cable with the wrong impedance it shoudl not matter too much.

So i don t understand why people give absolute value for cables, it it for the full cable ?
 

maverickronin

Major Contributor
Forum Donor
Joined
Jul 19, 2018
Messages
2,249
Likes
2,839
Location
Midwest, USA
Btw i don t get it, 30 year ago when i sutdied basic phyics (i went to math after) impedance and resitance was approximately linear in the length.
So if my switch is very short it should have low impedance and resistance -- simply by continuity and linearity --
so in a way if you have a 95% good connection and 5% of the cable with the wrong impedance it shoudl not matter too much.

So i don t understand why people give absolute value for cables, it it for the full cable ?

I'm hardly an expert in this either, but when talking about cable it is referring to characteristic impedance and transmission line theory. (Simple. Complicated.)
 
OP
Y

Yasser 06

Member
Joined
Dec 4, 2020
Messages
68
Likes
9
OP
Y

Yasser 06

Member
Joined
Dec 4, 2020
Messages
68
Likes
9
It should.
I have some RCA cables , from china they are independant (most are glued together) and well made (i paid may be 10euros for a pair and an EU audiophile shop would probably charge 50 euros fort that), i just replaced my coax cable by one of them and it is just the same. No quality loss at all which was to be expected.
 
Top Bottom