Should we care for S/N ratio when upgrading a car AMP?

[gabrielb]

I'm doing research before upgrading my car audio.
The HUD in modern car is so tightly integrate with the car that replacing it is out of question in most installation.
There are 2 common method for *adding* a new amplifier - either use the speaker-level input directly and adjust the input gain, or use a line input convertor (https://www.crutchfield.com/learn/n...evel-inputs-or-loc-line-output-converter.html).
In both cases we are amplifying the distorted signal coming from the HUD built in amplifier which means there is a very low ceiling on S/N ratio.

My understanding is that by amplifying the OEM signal we should be able to drive better speakers as the HUD built in amplifier has a very limited power (not sure if this is still true with class D amplifiers where raw power is very cheap).

But should we care about the aftermarket amplifier S/N or should we only check the power rating?

Did I missed something and there is a way to get the digital stream coming from the HUD which can be fed into a DAC/AMP combo?

 

[staticV3]

Did I missed something and there is a way to get the digital stream coming from the HUD which can be fed into a DAC/AMP combo?

If you have enough time and experience, you may be able to tap into the i2s connection going into the HUD's built-in DAC, then convert it to SPDIF using readily available converters, and connect your own DAC and Amp to that.

Basically like this, but without circuit diagrams to lead the way:
https://youtu.be/zkOqmpGewx0

 

[gabrielb]

If you have enough time and experience, you may be able to tap into the i2s connection going into the HUD's built-in DAC, then convert it to SPDIF using readily available converters, and connect your own DAC and Amp to that.

Basically like this, but without circuit diagrams to lead the way:
https://youtu.be/zkOqmpGewx0

I'm a SW guy, not licenced to touch HW
I spoke with 2 car audio installers and both insisted that I can't tap into the digital source and must use the speakers level input.
Should I keep looking for a more knowledgeable installer, or that this is an uncharted land?

 

[DVDdoug]

But should we care about the aftermarket amplifier S/N or should we only check the power rating?

No... But yes...

If there's a problem it's usually not the amplifier itself but noise getting-in from the car's electrical system. That's not going to show-up in the specs. Some amps are more susceptible to electrical noise than others but you won't know until you install it. Assuming the aftermarket amplifier has more power that usually means it also has more gain, which means any noise gets more-amplified.

I've never heard noise from a factory stereo, but I've had noise problems in some of my aftermarket setups. One amplifier I had made a loud thump when I shut-off the ignition. (I think it was OK if I shut off the stereo first.) That amp died and it was replaced. I also once had a ground loop problem that resulted in "alternator whine".

The automobile manufacturer may have used some wiring "tricks" or special filtering to eliminate noise in the factory setup. Usually an aftermarket amplifier has to be mounted in a different location and that makes it more prone to ground loop noise.

 

[staticV3]

Should I keep looking for a more knowledgeable installer, or that this is an uncharted land?

I doubt that there's an installer near you who'd attempt something like this.

That's squarely an enthusiast's DIY job.

Though if you're willing to do some light disassembly to tap into the amplifier outputs, then I don't see what would be stopping you from tapping into the Amplifier inputs instead, thereby increasing the SNR.

 

[DVDdoug]

I spoke with 2 car audio installers and both insisted that I can't tap into the digital source and must use the speakers level input.

Tapping-into the digital (or anything inside the unit) is "serious hacking". It's not something that a stereo shop is going to do and it's not something that the average DIY guy is going to do. I have tapped-into the line level signals once, but I wouldn't mess with the digital. ...Too much time & trouble and probably no (audible) benefit. (And I have an electronics degree and I work in electronics.)

I have two vehicles - A 2004 Honda Accord and an older full-size van. I installed a "killer" setup in the van myself. It's tri-amped with a pair of 12-inch subwoofers under the back seat. The head unit only has line-outputs.

The Honda still has the factor setup, except I had a car stereo shop add an iPod "pod" plug. It was a simple gizmo that plugs-into the back of the factory stereo but I'm not even sure how to remove/access the factory stereo, so I let someone else do it (I think the installation was free). I'm still using it but when the antique iPod classic dies (if it dies before the car dies ) I'll upgrade to Bluetooth, and again I'll let a car stereo shop figure it out. The Honda stereo is "unique" and a regular aftermarket stereo won't fit mechanically.

If I ever upgrade the amplification and speakers (which it "needs" but I'll probably never do), I'm not really sure if I'd attempt it myself. I'd need speaker-to-line converters, and I'd have to run power to the trunk and I'd probably have noise problems!

 

[gabrielb]

Actually, with the audio source all coming from my phone I could in theory install a Bluetooth DAC with LDAC support and connect its output directly to a class D car amplifier bypassing the HUD completely.
If the DAC has built in spotify/tidal I might be able to use it natively without BT by creating an access-point from my phone.

I can't be the first one coming with idea so there must be some ready product from miniDSP/SMSL/Topping in car format able to accept 12V power (I can probably use miniDSP Flex by adding a power convertor)

The main issue with this design that I won't have the car interface to control the music (I can use the phone of course, but it might be hard while driving).

 

[SIY]

"High quality sound in a car is like Arpège in a glue factory." - J. Gordon Holt.

 

[Palladium]

I doubt any distortion from the stock amps is audible at listening levels that aren't permanently damaging your hearing.

 

[gabrielb]

Another idea - Use active component speakers accepting digital wireless stream, plus an active SUB in the trunk.
Add a SW layer on the phone doing XO and room(i.e. car interior) correction.

Bluetooth might be bandwidth limited (assuming multiple speakers are driven by a single phone) so maybe should multiplex over wifi.

 

[gabrielb]

Actually, with the audio source all coming from my phone I could in theory install a Bluetooth DAC with LDAC support and connect its output directly to a class D car amplifier bypassing the HUD completely.
If the DAC has built in spotify/tidal I might be able to use it natively without BT by creating an access-point from my phone.

I can't be the first one coming with idea so there must be some ready product from miniDSP/SMSL/Topping in car format able to accept 12V power (I can probably use miniDSP Flex by adding a power convertor)

The main issue with this design that I won't have the car interface to control the music (I can use the phone of course, but it might be hard while driving).

Looks like it already exists - https://www.crutchfield.com/p_500PXEC808/Alpine-PXE-C80-88.html?tp=115.
Alpine PXE-C80-88 accept all kinds of input - USB, SPDIF & BT.
It has DSP interface you can run from your phone to manage all of its 8 channels - XO, phase shift, equalizer ...

 

[GXAlan]

Crutchfield is actually super knowledgeable about car audio with install photos and harnesses, etc.

What car do you have? Not every car applies hefty DSP at baseline (making it easy to modify and upgrade cheap cars). Amplifiers with internal DSP can let you correct a lot of the issues with the internal setup and things like JL Audio’s DSP are designed to correct your audio at a specific volume level.

 

[gabrielb]

Crutchfield is actually super knowledgeable about car audio with install photos and harnesses, etc.

What car do you have? Not every car applies hefty DSP at baseline (making it easy to modify and upgrade cheap cars). Amplifiers with internal DSP can let you correct a lot of the issues with the internal setup and things like JL Audio’s DSP are designed to correct your audio at a specific volume level.

I got Peugeot 2008.
Reading the Alpine PXE-C80 specs I saw that *in addition* to running DSP over analog input coming from the HUD (probably after applying ADC) it accepts various *direct* digital inputs which I accepts will be superior to the modified analog stream