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#### Jepalan

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I've a couple of questions regarding this subject:
1: How important is the line out impedance on the head unit with regards to noise? I never quite understood that specification. I am using an Eclipse CD8051 who's line-out impedance is lower than any other head unit's I've ever seen. But, like I said, I just don't understand the importance of the line-out impedance specification.
My 2 cents regarding your first question...

When it comes to line-level signals, lower output impedance is better, but in most cases doesn't make a big difference.
With line-level connections, we are trying to keep the RMS volts out of the HU higher than any noise that might get picked up along the way to the next device in the signal chain.
The logic behind wanting a lower output impedance is simple. Think voltage-divider.

Consider a simple single-ended connection scenario:
HU is modeled as a perfect voltage source followed by a series resistor equal to the output impedance.
Downstream device input(s) are modeled as a shunt resistor to ground equal to the device input impedance.

HU_RMS_VOLTS<-->100ohms<-->RCA cable<-->10Kohms<-->GND

The higher the output impedance, the lower the signal voltage on the RCA cable due to the voltage divider formed by the source's output impedance and the end-device's input impedance.
For example: If the source output impedance was equal to the load input impedance then the RCA signal voltage would be cut in half.

In practical application you don't need to worry too much about line-level output/input impedance unless you are driving a bunch of downstream devices via RCA splitters. In that case, each downstream device's input impedance sums in parallel and if the source device also has non-ideal (high) output impedance you may be attenuating the RCA signal voltage down too close to the noise floor.

#### glockcoma

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The fact this thread is almost 6 years old and has been covered many many times.

I've always wondered on forums why people are bothered when old threads are resurrected.
One of the ways to find this thread buried deep in its hole would be to use the search function.

If he would have posted a new topic with a question that's been answered a thousand times everyone would be preaching to use the search feature.

So which one is preferred?

#### nineball76

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I've always wondered on forums why people are bothered when old threads are resurrected.
One of the ways to find this thread buried deep in its hole would be to use the search function.

If he would have posted a new topic with a question that's been answered a thousand times everyone would be preaching to use the search feature.

So which one is preferred?
Bitching and nagging is the preferred method.

#### firebirdude

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I've always wondered on forums why people are bothered when old threads are resurrected.
One of the ways to find this thread buried deep in its hole would be to use the search function.

If he would have posted a new topic with a question that's been answered a thousand times everyone would be preaching to use the search feature.

So which one is preferred?
he wasn't asking a question. he was trying to answer a topic that was covered 6 years ago.

And heck yes, bitching is the way to go.

#### dsw1204

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My 2 cents regarding your first question...

When it comes to line-level signals, lower output impedance is better, but in most cases doesn't make a big difference.
With line-level connections, we are trying to keep the RMS volts out of the HU higher than any noise that might get picked up along the way to the next device in the signal chain.
The logic behind wanting a lower output impedance is simple. Think voltage-divider.

Consider a simple single-ended connection scenario:
HU is modeled as a perfect voltage source followed by a series resistor equal to the output impedance.
Downstream device input(s) are modeled as a shunt resistor to ground equal to the device input impedance.

Thanks for the info. It was helpful.

HU_RMS_VOLTS<-->100ohms<-->RCA cable<-->10Kohms<-->GND

The higher the output impedance, the lower the signal voltage on the RCA cable due to the voltage divider formed by the source's output impedance and the end-device's input impedance.
For example: If the source output impedance was equal to the load input impedance then the RCA signal voltage would be cut in half.

In practical application you don't need to worry too much about line-level output/input impedance unless you are driving a bunch of downstream devices via RCA splitters. In that case, each downstream device's input impedance sums in parallel and if the source device also has non-ideal (high) output impedance you may be attenuating the RCA signal voltage down too close to the noise floor.
Thanks for the information. It was helpful.

#### Jepalan

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he wasn't asking a question. he was trying to answer a topic that was covered 6 years ago.

And heck yes, bitching is the way to go.
Actually, I was responding to the poster ahead of me (ttocs338) and failed to notice *he* had resurrected a 6yr old thread... my bad... and now we are completely off-topic and bitching nits in a 6yr old thread

#### BMW Alpina

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I've always wondered on forums why people are bothered when old threads are resurrected.
One of the ways to find this thread buried deep in its hole would be to use the search function.

If he would have posted a new topic with a question that's been answered a thousand times everyone would be preaching to use the search feature.

So which one is preferred?
Bitching and nagging is the preferred method.
he wasn't asking a question. he was trying to answer a topic that was covered 6 years ago.

And heck yes, bitching is the way to go.
Actually, I was responding to the poster ahead of me (ttocs338) and failed to notice *he* had resurrected a 6yr old thread... my bad... and now we are completely off-topic and bitching nits in a 6yr old thread
Was reading this thread from beginning seriously, but can't help but laugh in the end
well, at least I gain more knowledge

#### geshat00

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Was reading this thread from beginning seriously, but can't help but laugh in the end
well, at least I gain more knowledge
Was that a pun "gain more knowledge"?

Sent from my HTC6535LVW using Tapatalk

#### thornygravy

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I'm sure like with anything there's diminishing returns at a certain point but going from a 1v preout to 2.5v and finally to recently 4v preouts.. each has sounded so much better (cleaner sounding at louder volumes) than the previous.

I know this is an old thread, but it's still something that gets asked about a lot.

#### KVH69

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I just want to know where people are getting balanced cables for car audio...? RCA is unbalanced so do you guys make your own XLR or TRS cables? Quite the mystery for me.

#### DarmoZ

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I have three amps, front(D), rear(AB), sub(D).
HU is 4v pre out.

Systems sound shit (muddy, distorted) When setting gains correctly. However can someone explain to me why my system sounds sooo much better (cleaner and better dynamic range, louder) When i go into the head unit xover section and reduce the gain on all channels to -8db (effectively lowering the head unit pre-out voltage) and then increasing the amp gain to compensate.

So essentially, like for like volume level:
Option A (HU pre-out normal, amp gains lower) - Music sound shit
Option B (HU pre-out lowered, amp gain higher) - Music sound better, as tracks should sound.

Note: I thought it was something wrong with my HU so i swapped it out to another brand/model also 4v. even replaced my iphone 6 to an iphone 8 in case it was the music source. Same thing as above applies still. So something to do with the amps maybe? electrical system?

#### instalher

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head unit output is clipping at 4 volts... just because it puts out 4 volts ac, dosnet mean its a clean unclipped signal... you wil need an oscope for that issue.. your ears hear are your best tool... My Pioneer head unit is 4 volt out as well but clipping starts at about 32 on the volume out of 40. No way am I getting the claimed 4 volts out, probably closer to 3, but I will take 3 clean vs 4 clipped any day.

#### thornygravy

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DarmoZ, cheaper 4 channel d classes tend to exhibit the behavior you're describing, in my experience.

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