Shield in high level outs - useless? High level real-world SQ for amping vs RCA

[barbaroja 10+ year member]

First post. Thanks for this great forum, I have learned a ton.

I have being reading about being better if using RCAs outs to amp because:

1. They are shielded plus less prone to picking noise.

2. They are not amped so no noise and distortion from HU.

About that, I have to ask:

1. Can you shield high level outs?

2. Can you also ground them as some people do in their pioneers when the pico fuses are blown? I understand alt noise comes from alt AC ripple and ground issues. This should help, but, would this make as a shield for rejecting other noise sources too?

3. I seriously doubt a decent HU would give such a bad amplification (talking about less than half the gain here) that, if reamped, it would be noticeable as a loss in sound quality. If someone has real world experience in comparing these two sounds (going high level to amp and going RCA to amp) please share.

4. I also read somewhere that high level outs when shielded, made bigger fields so they were noise generators. However, this was on a public address speakers article. Is this true for shielded and/or unshielded high level outs of the likes found in a HU?

If RCAs are good because of the noise rejection as I read, shielding speaker level outs should yield the same resilts, I think. However, the signal to noise ratio in a high level out would let you hear the noise only if hearing at very low volumes. So, I think a shielded cable be it RCA terminals or not, would pick the same amount of noise, just because it is a cable. Am I right?

Well, thats just my reasoning, but would be good some wxperience here, especially in the sound quality real-life experiment if using high level instead of RCAs.

Best, good day and again, thanks for this great forum!

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[barbaroja 10+ year member]

aw come on, 20 views...

 

[Wingman0121 10+ year member]

You can't ground a high-level or speaker level outputs because that'll fry your amp/headunit. RCA is different because it operates on the same ground as the headunit's chassis. An amplifier outputs AC instead of DC so grounding a speaker level output is like grounding the hot wire in your house.

You don't really need to shield speaker wires unless you KNOW noises are being picked up by the speaker wires and not anything else, and usually all you have to do is move it away from suspected noise source. I've read an old article about running the wires in copper tubes or wrap it in mylar(is it mylar?) shield but I think that's an overkill, not bad, but overkill.

 

[barbaroja 10+ year member]

OK got it. Any word about the sound quality in real world after using high outs to amp?

 

[Wingman0121 10+ year member]

OK got it. Any word about the sound quality in real world after using high outs to amp?

Using high outs to an amp will sound just as clean AS LONG AS the source amplifier is of high quality and low distortion. A lot of the times the factory headunits have built-in equalization/loudness, volume limiter and high-pass filter/bass blocker for their factory speaker so it is no good if the output isn't flat through 20~20kHz.

Preamp RCA outs are still the best way to go though.

 

[audioholic 5,000+ posts]

High level outputs, ie: speaker wires, are actually less susceptible to noise than are low level signals. They are called high level outputs because the signal has already been boosted by the h/u's internal amplifier, which means the 'signal' traveling through the wire is a higher voltage than the one in RCA's. Higher voltage signals are more immune to audible noise. The exact same reason a h/u with 8v RCA outputs is better than one with only 1v outputs.

High level outputs are considered inferior to low level RCA signalling because h/u amplifiers are notoriously noisy. Yes, even most good decks. Really high end decks have no amplifier at all, because the internal amp can introduce noise into the precious RCA outputs due to the field it's current generates. So these internal amplifiers create distortion, which it sends down the wire to the external amplifier, which adds its own distortion (called stacking distortion). And the external amplifier amplifies the distortion created by the h/u's amp, treating it just like any other piece of the signal it receives to amplify. This raises the audibility of the h/u's distortion even higher. Clearly a poor choice if fidelity is a goal.

 

[keep_hope_alive Premium Member]

Nicely put audioholic. Been enjoying the day, this was on my list.

To clarify answers to the OP's questions:

1. Yes. You can shield any wires by wrapping them in a conductive material, such as foil or copper braid. Then ground one or both ends of the shield. As audioholic said, you want a high signal to noise ratio. Speaker level outputs are a higher voltage output.

2. No. None of the high level outputs should be grounded. Most modern head units have a signal on both wires, similar to a bridged or balanced output. It is how they get higher voltage out. grounding one of them would short the deck. The Pioneer fix should not be applied to any head unit that does not have that issue.

3. The THD out of a head unit is very high relative to that of a decent pre-out voltage. As audioholic also said, you want to minimize stacking distortion. All of the distortion in the HU output is amplified by the amplifier. If your HU has a balanced or bridged output, and the amplifier has a balanced input, you can get some decent sound since distortion and noise in the HU may be common in both outputs.

4. Properly shielded wires won't generate noise outside the shield, that is what shields do. PA systems are quite different based on them operating on 70V systems and surrounded by AC fields and wire runs are hundreds of feet, even longer.

The reason we use RCA outputs is because distortion is minimized, much less than the speaker outputs. Ideally, we would have an optical output on the head unit and an optical in near our amps, to bypass the DAC's in the HU.

We want high signal strength so we minimize amplifier gain. More gain = more noise. We want gain as soon as possible, but we need the gain to be very low distortion. We also need the input impedance and output impedance to be adequate to maximize voltage gain across the interconnects. We achieve this with low output impedance and high input impedance.

Shielding does not eliminate any noise in the electrical signal before the cable. It only attempts to reject EMI and noise around the cable during it's run. In a car, we really don't have a lot of EMI that we cannot avoid with smart wire routing. Sielding will not have as much benefit on signal to noise as getting clean, high voltage output to begin with.

Operating the head unit at a lower volume to keep HU amp distortion low has the side effect of a low voltage output and higher amp gain. Defeats the purpose.

Hope that helps, feel free to ask more of these good questions.

 

[barbaroja 10+ year member]

Thanks for these straight answers. Any words about the line level converters, in case you do not have enough RCA outs? I have read about them and understand the basics, but I feel they cannot do anything for the stacked distortion...

I am helping a friend in an installation for replacing the stock speakers and adding a sub in a small car. We already got the sub and its amp, and we are replacing the stock speakers with comps and will add their amp later on. The stock HU is a pioneer with just 1 RCA (rear) out, so I will hook the comps amp to the high level outs, and the for the sub amp I will use the RCA. Suggestions appreciated.

 

[keep_hope_alive Premium Member]

many amps have an RCA pass-through, which let's you daisy chain amplifiers with RCA cables. i suggest getting an amp for the comp speaker that has that feature. if you get a 4 channel amp for the speakers (for bi-amp or bridging) make sure it has a 2 ch or 4 ch input selection so you don't need y-adapter cables.

line output converters (LOCs) are a necessary evil. David Navone makes some very nice LOCs but you're still dealing with the HU distortion.

in the past, i've added a 1/2 DIN equalizer that had a single RCA input and three RCA outputs. They can include a fader and sub level control as well as higher voltage outputs, crossovers, and EQ. you could add that to the head end to get the outputs and signal voltage you desire.

 

[barbaroja 10+ year member]

thanks for the input. the amp we are going to use for the comps is a cadence flash F400-4. Unfortunately, it does not have pass-through RCAs. The equalizer option sounds nice, thanks for that! I will probably implement it in my car in a near future, however for this particular installation, its kind of a minimalist one, very limited by budget, too, so will have to choose between using the high level outs or use a LOC for the fronts in order to retain fader control, also using a Y splitter to feed the sub with the rear signal.

SO, will have to choose between using a LOC or going high level... what would you choose?

 

[barbaroja 10+ year member]

would choose...

 

[audioholic 5,000+ posts]

Id only choose the LOC if it is required. Many amps these days dont accept high level signal wiring, so a LOC would be a necessity. But if your amp will accept high level inputs, Id go that route. A LOC is another component in the signal chain that will add its own distortion, increasing the stacking issue. keep_hope_alive is right that David Navone's LOC is a notoriously good piece, but it really adds nothing beneficial to a circuit that does not require altering your signal from high to low voltage.

 

[barbaroja 10+ year member]

Thanks a lot guys. This thread has been a success.

 

[keep_hope_alive Premium Member]

I agree with audioholic. Don't add what you don't have to.