What are the benefits to things that have balanced differential inputs?

[Jdunk54nl]

I got to thinking more about this today after a discussion with some others.


Most car audio has RCA outs that are single ended outputs. Quite a few devices are having balanced differential input stages via RCA's.

Example:
https://jlaudio.zendesk.com/hc/en-us...alanced-Inputs


I can see the benefits if using high level inputs because those should be balanced (signal on both wires and nothing grounded), but other issues arise with high level as we all know. But rca's are usually grounded at the source which would defeat the whole balanced and/or differential input.


I also do not see a bunch of benefits for balanced RCA's (2 wire things) as then you lose some other noise rejection properties from the shield normally being grounded in "normal" rcas. Hence the 3 wire/connections (XLR, TRS, ETC) normally for balanced with a dedicated ground/shield and dedicated signal wires.


Anyone help me see why this is a "thing" without sources being balanced? What am I missing?






Note for those that do not know: balanced and differential are usually combined but are not the same thing. Many people use these words interchangeably.

Balanced means both wires have the same impedance to ground, aka not grounded anywhere and both carry a signal.

Differential is where the source signal has one wire with an inverted polarity signal compared to the other wire. Upon reaching the amp, the amp switches this signal back and this process eliminates most noise picked up on the path.

[Justin Zazzi]

I'm curious too.

[geolemon]

This is the best concise explanation I've seen:

https://youtu.be/QOagVDZLQnA

Covers single-ended, differential - kinda inherently covers why balanced and differential go hand in hand also.

[Jdunk54nl]

Right, but doesn't the differential part also rely on the source being able to send out a differential signal? I always thought that both the source and the receiver had to be balanced to be balanced, and both had to be differential to be differential. If source is single ended, then that eliminates balanced right there so you'd lose all benefits of a balanced differential input.

Or am I missing something.....


Also I was given these documents to look over by another friend. I haven't gone completely through them yet, but so far it seems like what I said above is confirmed in these documents:

https://centralindianaaes.files.word...notes-v1-0.pdf


https://www.jensen-transformers.com/...ic-seminar.pdf

[Justin Zazzi]

Right, but doesn't the differential part also rely on the source being able to send out a differential signal? I always thought that both the source and the receiver had to be balanced to be balanced, and both had to be differential to be differential. If source is single ended, then that eliminates balanced right there so you'd lose all benefits of a balanced differential input.

Or am I missing something.....

You can mix differential and single-ended signal inputs and outputs, sometimes.

Differential inputs can accept differential signals and also single-ended signals.
Single-ended inputs can only accept single-ended signals.

One possible benefit of a differential input is it will be compatible with all consumer car audio gear which is typically single-ended, and also compatible with all professional and OEM gear like factory radios which are differential these days.

I'm cruising through the Whitlock paper from Jensen and it's full of great info. Lots to digest there.

[Jdunk54nl]

So then one benefit would be compatibility then. That makes sense.

[test13371997]

So im going to assume here that you are using the correct RCA for the type of rca input circuitry.

Single ended - coaxial

differential input - twitsted pair


On an amp that has single ended inputs, the shielding of the rca cable protects the middle pin(the actual signal) from getting noise. However if there is too much noise or simply a poor cable, noise will get in and you will get noise in your system.

On an amp that has differential inputs, whatever amount of noise gets "appended" to both conductors of the rca. There is no shield on the RCAs. And due to the way that differential input circuitry works, it looks at whatever is the same on both conductors. And since both conductors have the same noise, it gets removed.

Differential inputs are better

I only know of a single device that has *DIFFERENTIAL OUTPUTS*, and that would be a ford after you use for scan to convert the speaker wires into low level preouts.

[Jdunk54nl]

So im going to assume here that you are using the correct RCA for the type of rca input circuitry.

Single ended - coaxial

differential input - twitsted pair


On an amp that has single ended inputs, the shielding of the rca cable protects the middle pin(the actual signal) from getting noise. However if there is too much noise or simply a poor cable, noise will get in and you will get noise in your system.

On an amp that has differential inputs, whatever amount of noise gets "appended" to both conductors of the rca. There is no shield on the RCAs. And due to the way that differential input circuitry works, it looks at whatever is the same on both conductors. And since both conductors have the same noise, it gets removed.

Differential inputs are better

I only know of a single device that has *DIFFERENTIAL OUTPUTS*, and that would be a ford after you use for scan to convert the speaker wires into low level preouts.

Right. But does all of that differential input stuff still work with single ended outputs, which is the case for 99% of the audio sources I could find without getting into the pro level gear.

If the source you are using is a single ended single, that means there is not equal impedance to ground that is a must to be a balanced signal. It also isn't going to be differential, like you stated above 99% of the time.

So we are feeding these amps signals, from my understanding (after reading the Whitlock papers above) there is 0db of noise rejection.

The top picture is basically what would happened with a rca output to an amps rca input. Which is 0db noise rejection. We have tied the shield to the signal and ground on both ends. I don't think twisted pair would do anything if you can't separate the shield and lo signal side of the signal at the input end. I could be wrong about that though.

Page 29 from here: https://www.jensen-transformers.com/...ic-seminar.pdf

[Jdunk54nl]

I also want to re-iterate, I am just going based on what I can read on these things from respected sources. My knowledge is very limited here, which is why I posed the question.

I guess I am unsure of how many sources actually do not tie their shield or outer shell of the rca plug to ground. This could be an important thing as that could make them balanced outputs and would 100% fix my understanding.

[test13371997]

Right. But does all of that differential input stuff still work with single ended outputs, which is the case for 99% of the audio sources I could find without getting into the pro level gear.

If the source you are using is a single ended single, that means there is not equal impedance to ground that is a must to be a balanced signal. It also isn't going to be differential, like you stated above 99% of the time.

So we are feeding these amps signals, from my understanding (after reading the Whitlock papers above) there is 0db of noise rejection.

The top picture is basically what would happened with a rca output to an amps rca input. Which is 0db noise rejection. We have tied the shield to the signal and ground on both ends. I don't think twisted pair would do anything if you can't separate the shield and lo signal side of the signal at the input end. I could be wrong about that though.

Page 29 from here: https://www.jensen-transformers.com/...ic-seminar.pdf

Yes, differential input still works with single ended outputs. Mess with desmos.com https://imgur.com/a/pTpNdr2. a and b is the "ideal" or exactly what is coming out of the HU. Signal = ground. Since its a differential input, you use unshielded twisted pairs. That means that noise get radiated onto both conductors. So c and d is a and b plus the imaginary noise I came up with. When you do a-b and c-d, you get the same thing. You mention "balanced", but there are no balanced cables with RCAs in car audio. For a cable to be balanced, it needs to have 3 conductors. Which rcas dont have. Those pictures are talking about XLR adaptors and balanced stuff, which isn't a thing in car audio. I dont have anything to say about those pics