• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

Balanced TRS to unbalanced RCA - conflicting information

Curwen

Member
Joined
Jul 19, 2022
Messages
5
Likes
1
I have a MiniDSP Flex with balanced TRS outputs and I need to connect my SVS subwoofer which has an unbalanced RCA connector.

MiniDSP's recommend cable is different from RANE's system interconnect diagram (configuration 10b in the diagram).

Can anyone explain the benefits of using a 2 conductor cable where the shield is only connected at one end?

MiniDSP's recommended configuration

minidsp.png

RANE's recommended configuration

RANE.png
 

DVDdoug

Major Contributor
Joined
May 27, 2021
Messages
2,920
Likes
3,834
Either way is electrically the same because the white and shield are in parallel.
 

sarumbear

Master Contributor
Forum Donor
Joined
Aug 15, 2020
Messages
7,604
Likes
7,314
Location
UK
I have a MiniDSP Flex with balanced TRS outputs and I need to connect my SVS subwoofer which has an unbalanced RCA connector.

MiniDSP's recommend cable is different from RANE's system interconnect diagram (configuration 10b in the diagram).

Can anyone explain the benefits of using a 2 conductor cable where the shield is only connected at one end?

MiniDSP's recommended configuration

View attachment 219145
RANE's recommended configuration

View attachment 219147
That is one of the recommendation they gave. #11 is the same as niniDSP's and it is the better solution. #10b connects the grounds of the devices and does not benefit from the balanced output. Using the shield as a connection is not the best way to transfer signal.
 

DonH56

Master Contributor
Technical Expert
Forum Donor
Joined
Mar 15, 2016
Messages
7,835
Likes
16,497
Location
Monument, CO
Usually a balanced output has (+) and (-) sides that are in opposite polarity, and the same for the input. A balanced output if actively driven (directly or via transformer-coupled output) should not usually be shorted to ground. A balanced input may or may not "like" being shorted to ground since it will unbalance the input stage and upset the common-mode level. RANE's way is the way I would do it unless specifically advised otherwise by the manufacturer of the component I was connecting. That said, for the input, connecting the (-) input to ground (shield) is fairly common with the driving side's (-) output left floating.

IME/IMO - Don
 

DonH56

Master Contributor
Technical Expert
Forum Donor
Joined
Mar 15, 2016
Messages
7,835
Likes
16,497
Location
Monument, CO
There are 3 and a half types of balanced output stages. No single cable adapter or modified cable will work with all types of output stages.

Output stages:
1] transformer
2] Impedance / passive
3a] Active / powered (shortable)
3b] Active / powered ( NOT shortable)
Plus various flavors of "balanced" drivers, from fully-differential to quasi-differential to just impedance-matched (technically not a balanced output to me).
 
OP
C

Curwen

Member
Joined
Jul 19, 2022
Messages
5
Likes
1
If you'll notice, the diagram(s) use two different cable types.
I noticed, my question is whether anyone can explain the benefits of using a 2 conductor cable especially when the shield is only connected at one end?
 

DonH56

Master Contributor
Technical Expert
Forum Donor
Joined
Mar 15, 2016
Messages
7,835
Likes
16,497
Location
Monument, CO
I noticed, my question is whether anyone can explain the benefits of using a 2 conductor cable especially when the shield is only connected at one end?
The two-conductor-plus-shield cable (technically three conductors) lets signal return ("ground") current flow inside the shield, and the shield terminated on one end only provides a modicum of additional shielding from external noise. It also leaves the option available to replace the RCA with a TRS or XLR connector if in the future both ends of the cable plug into balanced components, or to add a transformer or active device at the RCA side to convert to a balanced cable run for higher common-mode noise rejection.

HTH - Don
 
OP
C

Curwen

Member
Joined
Jul 19, 2022
Messages
5
Likes
1
That is one of the recommendation they gave. #11 is the same as niniDSP's and it is the better solution.
Is #11 the same? To me, it looks like #11 is connecting the ring on the TRS which isn't what miniDSP is doing.

#10b connects the grounds of the devices and does not benefit from the balanced output. Using the shield as a connection is not the best way to transfer signal.
Is miniDSP's configuration not also connecting the grounds of devices given that the sleeves of both connectors are joined?

Apologies if I'm misunderstanding how this stuff works (new to audio science)
 

sarumbear

Master Contributor
Forum Donor
Joined
Aug 15, 2020
Messages
7,604
Likes
7,314
Location
UK
I noticed, my question is whether anyone can explain the benefits of using a 2 conductor cable especially when the shield is only connected at one end?

Shield is not a conductor. As the name suggests it shield's the conductors from EMF. A single wire cable with a shield should only be used when fixed cable impedance at RF frequencies is required. At those frequencies signal is almost always is modulated, hence ground loop is not a factor.

EM shielding (electromagnetic shielding) is the practice of surrounding electronics and cables with conductive or magnetic materials to guard against incoming or outgoing emissions of electromagnetic frequencies (EMF).
 

sarumbear

Master Contributor
Forum Donor
Joined
Aug 15, 2020
Messages
7,604
Likes
7,314
Location
UK
Is #11 the same? To me, it looks like #11 is connecting the ring on the TRS which isn't what miniDSP is doing.


Is miniDSP's configuration not also connecting the grounds of devices given that the sleeves of both connectors are joined?

Apologies if I'm misunderstanding how this stuff works (new to audio science)
Notice the note on #11
 
OP
C

Curwen

Member
Joined
Jul 19, 2022
Messages
5
Likes
1
Notice the note on #11
I thought the note implied an optional connection between ring and sleeve rather than optionally connecting the ring which appears to always be connected to black. Is it the same thing?
 
  • Like
Reactions: MCH

Lambda

Major Contributor
Joined
Mar 22, 2020
Messages
1,785
Likes
1,519
I noticed, my question is whether anyone can explain the benefits of using a 2 conductor cable especially when the shield is only connected at one end?
There are no real benefits.
Maybe in some special cases the 2 conductor cable will give sightly better shielding against electric fields.
But a proper Coaxial cable will give way better shielding against magnetic interference.

I would also add a resistor of around 600-2000Ohm From GND to the "cold or "-" or "R"
just in cases you want to use the cable with a transformer (equivalent) output.
 

DonH56

Master Contributor
Technical Expert
Forum Donor
Joined
Mar 15, 2016
Messages
7,835
Likes
16,497
Location
Monument, CO

Piere

Active Member
Joined
Feb 24, 2022
Messages
195
Likes
190
To summarise regarding the balanced Flex:

On the Output Jack both "+" (Tip) and "-" (Ring) are hard driven by an opamp. Normally a balanced output is floating and you should connect "Ring" to GND. But in this case NOT. Keep Ring not connected. Otherwise you will short the opamp output to GND. Tip is the signal conductor to the pin of the RCA connector

On the Input side both "+" (Tip) and "-" (Ring) are inputs. To avoid excessive noise you must NOT left Ring floating and connect it to GND.

How you do this with different kind of cables (balanced or not) is a debate by itself, see Sams post.

So Output leads and Input leads are not the same and not interchangeable. To circumvent this I myself connect Ring to GND through a 330 - 560 ohm resistor. It's sufficient low to short the signal at the input to GND and avoid excessive noise. And used as an output lead it does not short the opamp.
 

yavormoskov

Active Member
Joined
Apr 9, 2019
Messages
132
Likes
107
Location
Atlanta, USA
That is one of the recommendations they gave. #11 is the same as niniDSP's and it is the better solution. #10b connects the grounds of the devices and does not benefit from the balanced output. Using the shield as a connection is not the best way to transfer signal.
This is absolutely correct. I used to make a lot of cables myself but now I primarily order them. Got lazy I suppose :)
 

Lambda

Major Contributor
Joined
Mar 22, 2020
Messages
1,785
Likes
1,519
On the Output Jack both "+" (Tip) and "-" (Ring) are hard driven by an opamp. Normally a balanced output is floating and you should connect "Ring" to GND. But in this case NOT. Keep Ring not connected. Otherwise you will short the opamp output to GND. Tip is the signal conductor to the pin of the RCA connector

On the Input side both "+" (Tip) and "-" (Ring) are inputs. To avoid excessive noise you must NOT left Ring floating and connect it to GND.
This is why i recommend to connect ring via a resistor. this way the cable is comparabil as input and output and can be driven by opamps as well as with an isolated floating transformer like output.
 
Top Bottom