Differential input amplifiers

[79Bronco]

Some higher end amplifiers have differential RCA inputs to isolate 12v to ground to help with noise.

Great technology, but do you have to have a head unit that will "output" a differential signal. If so, how can I tell?

Sorry if this is a dumb question, but I'm currently running coaxial RCAs on my amplifier with the RCA's at the head unit grounded to the head unit's chassis. (Gotta love pioneer)

Just looking to upgrade my cabling to twisted pairs if I can, thanks

[will77530]

interested to see what others say cause i have no idea what ur talking about

[Azagtoth502]

This covers similar iirc

http://www.stevemeadedesigns.com/board/topic/162518-truth-about-rca-cables-coax-vs-twisted-pair/

[79Bronco]

While that is a great, and very informative, video. It does not answer my question. The amp may have the technology to "read" the twisted pair signal, but does the head unit output a differential signal?

[will77530]

i dont think the headunits have the capability to do so i think they are just sending a low level signal and then the amp processes it in one of the two ways listed in the video unless you are using optical than thats completelly diferent

[Azagtoth502]

Saw things about some factory radios having them.

Hell I'd email D'Amore direct and ask him or maybe post this in his section and he'll see it.

[79Bronco]

i dont think the headunits have the capability to do so i think they are just sending a low level signal and then the amp processes it in one of the two ways listed in the video unless you are using optical than thats completelly diferent

If there are 0 head units on the market with this capability, then why does the technology exist? Seems a little backwards.

Saw things about some factory radios having them.

Hell I'd email D'Amore direct and ask him or maybe post this in his section and he'll see it.

Last time I posted in that section with a cable question, it took 3 months for a reply. Tony is a very busy man.

[8ight]

Some extremely high end (Denon, etc) head units have balanced outputs but most of the time you just use a transmitter like this http://www.ebay.com/itm/New-Zapco-SLDIN-T-Symbilink-/130567865573 or a line driver.

[Wicks]

Some higher end amplifiers have differential RCA inputs to isolate 12v to ground to help with noise.

Great technology, but do you have to have a head unit that will "output" a differential signal. If so, how can I tell?

Sorry if this is a dumb question, but I'm currently running coaxial RCAs on my amplifier with the RCA's at the head unit grounded to the head unit's chassis. (Gotta love pioneer)

Just looking to upgrade my cabling to twisted pairs if I can, thanks

My first question is why do you think that twisted pair cables are an "upgrade"?

Don't believe all the marketing hype that you see.

Your best cable option is the cable that properly transfers your available signal between the HU and amp/processor/etc.

For a balanced/differential signal to work properly, you need a HU that outputs that type of signal. You also need an amp/processor that accepts and processes the signal as well.

Will a system work if you mis-match parts, sure it could but you wont be getting full use of the noise cancelling ability of the twisted pair cable.

When used properly a coax cable will also have great noise reducing ability as well.

You mentioned Pioneer for a HU and that you may have the pico fuse issue. cabling can only do so much of other components are faulty.

As said above, very few HU's have balanced outputs, especially aftermarket ones. So you most likely have a single-ended HU.

As you saw in Tony D's video, the best option for that output is coax.

If you absolutely have to have twisted pair, then as mentioned above, you could get a converter to change your signal from one to another.

If you'd like to test for it then do the following:

Read your manual(s) and see if your equipment supports balanced/differential signals. If they do then the manuals should say so.....OR

Play a test tone on your HU at full volume (rest of the system disconnected obviously) or at least decent volume where you'll get a solid RCA output voltage to read.

Place the ground lead of your DMM on the HU's chassis. Set the DMM to Vac.

Probe the center conductor of your RCA pre-outs with the positive DMM lead (F, R, SUB RCA should all work assuming you have your settings flat and nothing is attenuated).

You should get a reading that is inline with your "rated" RCA output voltage if you use a 0dB test tone.

Now use the positive probe and look at the outside conductor of the RCA output.

If you have balanced/differential outputs then you should see the same signal voltage there as with the center conductor.

If you did see a signal on the outside conductor then you can also use the DMM probes between the outside and inside conductor of the RCA jacks and you should see double the voltage you did on the previous measurements.

Another check you could do is to set the DMM to ohms and measure the resistance between the outside of the RCA jack to the chassis of the HU. Make sure everything is Powered off, system disconnected).

If you have single-ended outputs then you should see a very low (~0.4 Ohm) reading.

If you have balanced/differential outputs then you should see a high resistance.

There is a catch though. If you have a "pico fuse" issue then the connection between your HU chassis and RCA outside conductor has been compromised so you'll get a false reading.

[79Bronco]

Some extremely high end (Denon, etc) head units have balanced outputs but most of the time you just use a transmitter like this http://www.ebay.com/itm/New-Zapco-SLDIN-T-Symbilink-/130567865573 or a line driver.

8ight- Thanks for that link. I'm currently running the soundstream reference amplifiers, and they have the option to run a symbilink-style balanced input. It is a 6-pin mini-din type connector that looks just like what you have posted above. Guess I'll be ordering a couple of those

Some higher end amplifiers have differential RCA inputs to isolate 12v to ground to help with noise.

Great technology, but do you have to have a head unit that will "output" a differential signal. If so, how can I tell?

Sorry if this is a dumb question, but I'm currently running coaxial RCAs on my amplifier with the RCA's at the head unit grounded to the head unit's chassis. (Gotta love pioneer)

Just looking to upgrade my cabling to twisted pairs if I can, thanks

My first question is why do you think that twisted pair cables are an "upgrade"?

Don't believe all the marketing hype that you see.

Your best cable option is the cable that properly transfers your available signal between the HU and amp/processor/etc.

For a balanced/differential signal to work properly, you need a HU that outputs that type of signal. You also need an amp/processor that accepts and processes the signal as well.

Will a system work if you mis-match parts, sure it could but you wont be getting full use of the noise cancelling ability of the twisted pair cable.

When used properly a coax cable will also have great noise reducing ability as well.

You mentioned Pioneer for a HU and that you may have the pico fuse issue. cabling can only do so much of other components are faulty.

As said above, very few HU's have balanced outputs, especially aftermarket ones. So you most likely have a single-ended HU.

As you saw in Tony D's video, the best option for that output is coax.

If you absolutely have to have twisted pair, then as mentioned above, you could get a converter to change your signal from one to another.

If you'd like to test for it then do the following:

Read your manual(s) and see if your equipment supports balanced/differential signals. If they do then the manuals should say so.....OR

Play a test tone on your HU at full volume (rest of the system disconnected obviously) or at least decent volume where you'll get a solid RCA output voltage to read.

Place the ground lead of your DMM on the HU's chassis. Set the DMM to Vac.

Probe the center conductor of your RCA pre-outs with the positive DMM lead (F, R, SUB RCA should all work assuming you have your settings flat and nothing is attenuated).

You should get a reading that is inline with your "rated" RCA output voltage if you use a 0dB test tone.

Now use the positive probe and look at the outside conductor of the RCA output.

If you have balanced/differential outputs then you should see the same signal voltage there as with the center conductor.

If you did see a signal on the outside conductor then you can also use the DMM probes between the outside and inside conductor of the RCA jacks and you should see double the voltage you did on the previous measurements.

Another check you could do is to set the DMM to ohms and measure the resistance between the outside of the RCA jack to the chassis of the HU. Make sure everything is Powered off, system disconnected).

If you have single-ended outputs then you should see a very low (~0.4 Ohm) reading.

If you have balanced/differential outputs then you should see a high resistance.

There is a catch though. If you have a "pico fuse" issue then the connection between your HU chassis and RCA outside conductor has been compromised so you'll get a false reading.

Great info here, thank you for the response. Why do I think twisted pair would be an upgrade? Because anything would be an upgrade over the el-cheapo dollar store type RCAs that I'm currently using. I guess I'll be ordering the symbilink type connector and running that.

Thanks