Balanced TRS to unbalanced RCA - conflicting information

[Curwen]

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

RANE's recommended configuration

 

[DVDdoug]

Either way is electrically the same because the white and shield are in parallel.

 

[sarumbear]

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]

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

 

[puppet]

If you'll notice, the diagram(s) use two different cable types.

 

[Speedskater]

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)

 

[DonH56]

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).

 

[Curwen]

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]

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

 

[Curwen]

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]

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).

What is EM shielding (electromagnetic shielding)? | Definition from TechTarget

Learn how EM shielding -- the use of materials and techniques to prevent electromagnetic interference from affecting electronic components -- works.

www.techtarget.com

 

[sarumbear]

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

 

[Curwen]

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?

 

[Lambda]

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]

This picture might help: https://www.audiosciencereview.com/...d-balanced-unbalanced-and-all-that-jazz.1352/ It does not show the case of a quasi-balanced input or output with only impedance matching and not fully differential circuitry.

 

[sam_adams]

Hopefully, the papers linked below will stem the tide of confusion around this subject:

Bill Whitlock - Interconnection of Balanced and Unbalanced Equipment - Jensen AN - 003

Bill Whitlock - The Myth and Mystery of Analog Signal Interfaces - AES Detroit - 2021

Most importantly, take note of the shield connections in the Jensen tech note.

 

[Piere]

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]

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]

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.

 

[Speedskater]

Plus various flavors of "balanced" drivers, from fully-differential to quasi-differential to just impedance-matched (technically not a balanced output to me).

Meanwhile, I have the exact opposite viewpoint.