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Old 1st November 2013, 15:27   #1
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Default Amps with high-level inputs VS Line output converters

While upgrading the ICE and retaining the stock HU which in most cases don't have a RCA/pre-out, what is a better approach:

1. Getting an amp which can take high-level inputs and connecting the speaker outputs from the HU directly to this?

2. Getting line output converters (also referred to as hi-lo converters) between the speaker outputs from the HU and an amp (even if the amp can accept high-level inputs)?

My question is specifically for a Mahindra XUV500, but I felt that this might be a question that is relevant to others wanting to upgrade their stock ICE setups without replacing the HU.

PS: Mods, I couldn't find a thread regarding this on Team-BHP - apologies if we already have a discussion taking place on this.
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Old 1st November 2013, 15:49   #2
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Default re: Amps with high-level inputs VS Line output converters

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Originally Posted by TNAWAYAJ View Post
While upgrading the ICE and retaining the stock HU which in most cases don't have a RCA/pre-out, what is a better approach:

1. Getting an amp which can take high-level inputs and connecting the speaker outputs from the HU directly to this?

2. Getting line output converters (also referred to as hi-lo converters) between the speaker outputs from the HU and an amp (even if the amp can accept high-level inputs)?.
Get hi-lo converters. They have a shield and hence the system will be less susceptible to engine noise.
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Old 1st November 2013, 17:16   #3
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Default Re: Amps with high-level inputs VS Line output converters

Some say that putting an external LoC also brings in some noise. Haven't personally experienced any noise wherever I have seen an installation with an LoC. Of course, any installation does well with competent and neat work.

Only a few amps are available with built-in LoC. It all then depends on whether you get one or not. If you don't an external LoC is a must. Better to use LoC than having to wait for an amp with built-in LoC to be available.

Last edited by DerAlte : 1st November 2013 at 17:20.
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Old 6th November 2013, 19:31   #4
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Default Re: Amps with high-level inputs VS Line output converters

Thanks DelAlte and Navin!

Another interesting thing that I came across is that some of the newer amps that can accept high-level inputs, do so with varying limits.

For example, the JBL GTO804EZ can take up to 15v (I had no idea HUs can pump out such high voltage signals to speakers, I believe the XUV HU is known to be a little eccentric when it comes to this), while the Focal Solid 4 can take up to 5v.

I am going to be upgrading the ICE on my XUV500 soon - have decided on the Focal Solid 4 - will see if the LOCs are necessary / beneficial and take a call during installation.

Even with LOCs, there are the advanced ones like the Audio Control LC series which actually have some signal summing capabilities, and then there are the simpler passive ones like the ones from Rockford Fosgate or Scosche.

With all the rumours about unwanted incessant hiss coming through on XUV ICE upgrades, I'll need to figure the LOC setup carefully too.

Will post updates as and when they happen!

Thanks!
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Old 6th November 2013, 22:42   #5
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Default Re: Amps with high-level inputs VS Line output converters

any suggestions on the external Line out Converters?

I am currently using a 4 channel scosche converter,SLC-4, bought from USA, which is totally crap, as I have no depth in sound or Bass.

The other is a LOC by Audison, SLI-4 , IIRC, 4 channel & it brings out the sound nicely, though expensive at about 5k.

Any other suggestions for a four channel output as I intend to connect two amps (4-channel & Mono) in my Corolla
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Old 6th November 2013, 23:32   #6
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Default Re: Amps with high-level inputs VS Line output converters

I have done hundreds of installs with amps accepting high level inputs of almost all the oem head units, and never faced a problem with noise or any other issues. The BIG advantage of using high level inputs however is that you don't have to provide a remote turn on line from ignition etc.
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Old 7th November 2013, 00:34   #7
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Default Re: Amps with high-level inputs VS Line output converters

In my opinion, cost is a major factor. Most Hi Lo convertors cost a fair amount, and I'd rather invest that elsewhere in the ice. If you think you are buying a high quality convertor, your amp might end up being the bottleneck. If you use the built in Hi Lo Convertor, you don't have to worry about that
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Old 7th November 2013, 10:49   #8
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Default Re: Amps with high-level inputs VS Line output converters

Quote:
Originally Posted by TNAWAYAJ View Post
I am going to be upgrading the ICE on my XUV500 soon - have decided on the Focal Solid 4 - will see if the LOCs are necessary / beneficial and take a call during installation.

Even with LOCs, there are the advanced ones like the Audio Control LC series which actually have some signal summing capabilities, and then there are the simpler passive ones like the ones from Rockford Fosgate or Scosche.
Unless you are going in for some really high end application, you dont need something as sophisticated as Audio Control. I think the Audison one will do just fine.

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Originally Posted by Bass&Trouble View Post
I have done hundreds of installs with amps accepting high level inputs of almost all the oem head units, and never faced a problem with noise or any other issues. The BIG advantage of using high level inputs however is that you don't have to provide a remote turn on line from ignition etc.
At the risk of challenging a professional I would like to say the following:

Maybe I am old fashined but I dont see any reason to first amplify a signal (to speaker level by the HU) then attenuate the same signal (by the amplifier) and then amplify it back to speaker level (again by the amplifier). In my my view the simpler the signal path the better.

Besides RCA cable construction is a outer sheild (which goes to ground) and an inner hot (signal) wire. As long as you dont have any ground loops in yoru wiring and are not running the RCA cable along side power cables this signal will be cleaner than a speaker level wire which is 2 parallel wire (like lamp cord).

In addition the preamp (on the HU) will most likely have a better S/N ratio on the RCA out that t speaker out.

Last edited by navin : 7th November 2013 at 10:52.
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Old 7th November 2013, 23:20   #9
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I dont see any reason to first amplify a signal (to speaker level by the HU) then attenuate the same signal (by the amplifier) and then amplify it back to speaker level (again by the amplifier).
That's why I said OEM deck baba. Where there is no option, only speaker level signal.

In fact with poor quality converters or ones without enough wattage, things can end up sounding pretty bad.
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Old 8th November 2013, 10:34   #10
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Default Re: Amps with high-level inputs VS Line output converters

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Originally Posted by Bass&Trouble View Post
That's why I said OEM deck baba. Where there is no option, only speaker level signal.
With a speaker level signal a LOC will attenuate the signal close to the OEM HU and then you run RCAs from the LOC to the amplifier. Something like the products below.
http://www.crutchfield.com/p_142SLC4/Scosche-SLC4.html
http://www.crutchfield.com/p_161LC2I....html?tp=61671

Using the speaker level input on the amplifier means that the speaker level input is fed to the amplifier which then attenuates the signal (probably via a resistance bridge) and then uses this signal for it's internal circuits.

So in either case the we have to pad the signal down and then amplify it. I have not done a A-B test comparing a LOC vs speaker level inputs but I figure given than an RCA cable uses the return leg as shield it would be cleaner to do this via a LOC. Right? Wrong? If later, why?
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Old 8th November 2013, 11:24   #11
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Default Re: Amps with high-level inputs VS Line output converters

navin, i used to think that the conversion happens via a resistor network in the LOC , but then realized that we are using an amp with a bridged output, and though the ground from the HU may not be available, and we will end up losing some part of the signal if we use some sort of passive resistor/divider network. What I found instead was
http://www.bcae1.com/loc.htm
apparently transformers are used.

In an amp with a Speaker level input
I used this kenwood service manual as an example
http://smdcode.com/en/detail/pdf/ser...ice-manual.pdf
the signal is attenuated using resistors, the Decoupled using caps, and then the input fed to the differential inputs of one of the op amp stages. The input is on the top of Page 7, and ends up at the IC2/3 inputs in page 6

Though the RC network might reduce bandwidth, so will the transformer, and speaker level signals should be more immune to noise and interference - Think of it as a ultra low output impedance, 14.4V balanced preout, and an amp with the corresponding inputs

Last edited by greenhorn : 8th November 2013 at 11:27.
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Old 8th November 2013, 11:41   #12
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Default Re: Amps with high-level inputs VS Line output converters

IMHO there is hardly any difference between the 2 cases, save for the possibility of induced EMI if the cable between the Speaker tap off point to the amp's high level input is untwisted or unshielded.

* The Speaker level side would carry ~24-36V p-p, whereas the post-attenuation it will be 2-6V p-p with an LoC
* The induced EMI on 24-36V p-p would get attenuated along with the signal in the pad (both with an Loc as wells with built-in attenuator in amp)
* The induced EMI would be (almost) obviated if the connecting cable is at least twisted (like some old SCSI flat cables) if not shielded
* The RCA cable from LoC can also be dicey depending on the basic cable used. If it is one of those that has sparsely woven shield and one core, then gone case (even in regular cases with HUs that have Pre-out terminated on RCA sockets). Some RCA cables are made out of cables that have a twisted pair for each channel, with 2 (or more) twisted pairs then being shielded with a woven shield

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... Though the RC network might reduce bandwidth, so will the transformer, and speaker level signals should be more immune to noise and interference - ...
Why would they limit bandwidth? That's an empirical myth. Even mag pickups in turntables, and dynamic microphones, used/use small signal impedance-matching trafos. The RC network values are calculated to be good till 300Khz or so.

Last edited by DerAlte : 8th November 2013 at 11:57.
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Old 8th November 2013, 12:08   #13
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Default Re: Amps with high-level inputs VS Line output converters

I was just saying theoretically, an case could be made. a 1Hz LPF will work fine for any audio, but still technically, its bandwidth is limited, and there would be someone out there who will say it is lossy, and is willing to pay pretty penny for that last .01dB or so

Last edited by greenhorn : 8th November 2013 at 12:12.
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