Advice about sound cards please !

[ssbb1fire]

Hello guys, I hope I'm posting in the right place, it's the first time I write something on this forum.
I have a friend who would like to connect its UMC404HD to a pair of passive loudspeakers, wich are 2 Infinity Primus 150.
I've done some research and here's what I found :
connecting directely the passive loudspeaker to the main output (either XLR or 1/4" jacks) will work but will damage the sound card in the long run.
The solution is to use an amplifier between them.
I've chosen this one : AIYIMA A07 Amplifier Stereo Class D TPA3255 2x225W 4 Ohm - Audiophonics
Here's how I think of it :
I'll make him a cable wich goes from his jacks main outputs to the RCA of the amplifier (so I need to make 2 Jack-RCA mono cables) and I'll just make a regular loudspeaker cable from the amplifier to the loudspeakers.
What do you think ? Do you see any flaws ?
My main concern is I'm not sur about the main line output going into the RCA input of the amplifier.
Thanks in advance.

 

[MAAC0]

connecting directely the passive loudspeaker to the main output (either XLR or 1/4" jacks) will work but will damage the sound card in the long run

Why ? sound card can be shorted as op-amps have bult-in protections.
The least you can expect is low volume since it is line level.

What do you think ? Do you see any flaws ?

This is how it is supposed to work. If the outputs are balanced, use stereo jacks and leave the ring floating (inverting output).
Turn the volume down, since it will probably clip the input of the amp (Pro to consumer levels) or use some resistive attenuators.
Use the playback RCA outputs. Problem solved.

 

[linuxfan]

I agree with MAAC0 on most points, except the hack of using 2 pins of of the balanced outputs as an unbalanced signal.

The AIYIMA A07 has unbalanced inputs (actually its amp circuit is balanced, and the amp board can be adapted for balanced input - but that's another story) so give it an unbalanced signal, which the Behringer UMC404HD provides - at the RCA jacks marked "MAIN OUT L R".

 

[ssbb1fire]

Why ? sound card can be shorted as op-amps have bult-in protections.
The least you can expect is low volume since it is line level.

What I mean is that if you want a correct volume you'll ask the sound card for a power she can't produce it will damage the card even with protection, no ?
Or will it just not work ?

This is how it is supposed to work. If the outputs are balanced, use stereo jacks and leave the ring floating (inverting output).
Turn the volume down, since it will probably clip the input of the amp (Pro to consumer levels) or use some resistive attenuators.
Use the playback RCA outputs. Problem solved.

I don't want to use the RCA Playbacks beacuse it only plays what comes from the PC, wich means you can't hear your 1 to 4 inputs while playing.
I have to use the main outs, either XLRs or Jacks.
I don't know how to check if the output is balanced if it is not noted in the manual. I'll look today

Still, if I understood correctly what you said, using the jack main outputs, with cables that go from jack to rca to connect it to the amplifier will work fine, am I right ?

 

[linuxfan]

I don't want to use the RCA Playbacks beacuse it only plays what comes from the PC, wich means you can't hear your 1 to 4 inputs while playing.
I have to use the main outs, either XLRs or Jacks.

Oops sorry, when I looked at images of the rear panel of UMC404HD I thought that I saw RCA sockets for "MAIN OUT" but I now realise these are TRS sockets. Behringer has provided these as dual-purpose balanced/unbalanced outputs. Since your amplifier's inputs are unbalanced, then these are the outputs Behringer intended you to use - you need 2x 1/4" mono-to-RCA cables to connect between UMC404HD and amplifier -
https://www.amazon.com/Hosa-CPR-202-Stereo-Interconnect-Meters/dp/B000068O17
or
TISINO Dual 1/4 inch TS Male to Dual RCA Male Audio Interconnect Cable Patch Cable Cords -3.3 ft: Amazon.com.au: Home
If you are wondering how a 1/4" TS plug works when plugged into a TRS socket, it's explained here -
audio - Why does this balanced/unbalanced setup work? - Sound Design Stack Exchange

When mapping a TRS or TS connector to balanced conductors, you are mapping the following:

Tip -> Signal +ve
Ring -> Signal -ve
Sleeve -> Ground.

When there is no ring, the Sleeve is increased in size and thus the mapping is as follows:

Sleeve -> Signal -ve, Ground

Signal-ve and Ground are bridged, which is the correct way of unbalancing a balanced signal.

This is similar, then, to the wiring that MAAC0 suggested, except that the balanced -ve pin and GND are both grounded at the unbalanced end. This is what the Behringer engineers intended.

 

[ssbb1fire]

Ok man, I've read what you said a lot of times, and even tho I don't fully understand everything, I've tried my best to do so.
I still need to clear something :
Should I make TS 1/4" to RC or TRS 1/4" to RCA ?
I don't understand how I should choose, apparently both works, they are just different mappings.

I'm also not very sure about the mapping I should do, can you explain it again ? I'm sorry but there are a lot of specific expressions that are used (like leave the ring "floating") wich I don't directly understand.

Thanks a lot for your help.

 

[MAAC0]

you'll ask the sound card for a power she can't produce it will damage the card even with protection,

No, it will simply clip because You have to play louder than normal operation & probably the op-amps get a bit warmer. The same would also happen with line connection when played loud. The difference here perhaps is it will clip earlier due higher current demand.
When You hear the clipping distortion that's Your limit.
After this limit op-amp protection kicks in.

Should I make TS 1/4" to RC or TRS 1/4" to RCA ?

I don't understand how I should choose, apparently both works, they are just different mappings.

This is what the Behringer engineers intended.

Most Behringer gear adapts (raises) the signal when cold (ring) is shorted.
If it were a "standard" balanced connection, with inverting op-amp for cold signal You would loose 6dB by only connecting the hot signal. Remember cold signal gets inverted at the receiver end and is summed with the hot signal.

Ring floating means not connected. That's why I suggest TRS (Stereo) jacks since the the ring (cold output) doesn't get shorted. The price difference doesn't justify.
Try ring floating first. Short with sleeve if You get & need a stronger output.

Signal-ve and Ground are bridged, which is the correct way of unbalancing a balanced signal.

Yes, for inputs !! For outputs depends on the type of output.

Have fun reading

https://mikeriversaudio.files.wordpress.com/2010/12/balanced-unbalanced_revised.pdf
https://toonz.ca/bose/wiki/images/d/d1/Sound_System_Interconnection.pdf

You can also connect ground to cold & RCA tip to hot and leave sleeve floating, but I don't recommend it since it defeats the purpose of the cable shield. But it also works with a small cable. Think the sleeve acting as a Faraday cage between two units.

 

[ssbb1fire]

I suggest TRS (Stereo) jacks since the the ring (cold output) doesn't get shorted. The price difference doesn't justify.
Try ring floating first.

I've read the document "sound system interconnection", and what you describe is the connection number 10 page 7, am I right ?
If that's so, I would make the cable with this :
Neutrik NP3 X – Thomann France
pro snake 63000 – Thomann France
Amphenol ACPR-RED – Thomann France
and use the wiring shown as number 10 page 7.
I think that's it !
What do you think ?
Thanks a lot for your help !

 

[MAAC0]

Yes. Try with & without the short.
Assemble the cable with ring floating and then use a screwdriver to short the ring and hear the difference.