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Old 02-02-2019, 10:58 AM   #1
Andrew325is
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SQ: Factory vs. Aftermarket

This may be obvious, but for those who know, which setup is going to produce the best sound?

1: Alpine CM5908 with factory amp

2: Aftermarket Alpine CDE-HD149BT with amp bypass

How does the factory HU compare to a new HU if the factory amp is replaced with aftermarket?
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Old 02-02-2019, 11:58 AM   #2
bradnic
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How about trying it and telling us?

In fairness to the factory setup, both the head unit and power amp should be electrically restored first. Even then the factory amp used speaker level inputs which will never beat properly shielded line level inputs. In order of quality I suspect the following is true

1) aftermarket HU, line level to a low THD aftermarket amp
2) factory HU modded with line level out, low THD aftermarket amp
3) electrically restored factory premium setup
4) aftermarket speaker level output to aftermarket amp
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Old 02-05-2019, 01:59 AM   #3
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I have the original stereo and amp the previous owner cut out. I don’t know what condition they are in as far as if they function properly. I’m going to keep them, but I don’t want them in the car if the aftermarket HU provides better SQ. I’d have to wire them in to test them and I’m not going to do that if I install the aftermarket HU. There is also no point in restoring the old units (if they need that) if they are just going to be sitting in a box. When and if the time came I wanted to use them (or a future owner) then they could be restored if necessary.
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Old 02-05-2019, 11:04 AM   #4
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If powering the speakers from a head unit, ANY head unit, the sound quality will be the same (not great). No single-DIN head unit, factory or aftermarket, has a step-up DC-DC converter, so all of them power the internal amp chips from Vbattery. What this means is that, for a 4 Ohm nominal speaker, you are not going to be able to deliver more than ~15W-RMS to the speaker before massive distortion (>10%) sets in.

So, if an aftermarket HU has some functional features that you like, then there's a good reason to get one. From a sound quality standpoint, do not expect much and certainly don't spend more on any HU that promises to deliver it, because it is physically impossible. The internal amp ICs that HUs use have improved a little in the last 30 years, but not enough to really matter. The "50Wx4" marketing nonsense refers explicitly to the DC power that can be delivered to a 4 Ohm resistor with Vbattery-14.14V, and has nothing to do with audio.

The only way to get high quality, LOUD sound reproduction in the car is to use an aftermarket amplifier. I have no idea what the specs on the factory amp are, but just based on its size and age (pre-dating high efficiency class-D designs), I would guess that it is not capable of providing much more power delivery than the head unit. Almost any aftermarket amp that is spec'ed at 50W-RMS x 4 should be fine, and is almost guaranteed to deliver vastly better audio performance than driving speakers from the HU. Achieving this also requires some wiring work to make sure that there are no ground loops or alternator noise, but that is usually pretty straightforward.

Regarding pre-amp signals vs speaker-level signals, you can get good results from both if you are intelligent with how you wire things.
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Old 02-06-2019, 08:44 AM   #5
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^^ good advice, info here. Spot on
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Old 02-06-2019, 09:23 AM   #6
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Here is another option to consider:
Run a Dayton DSP-408 with the Bluetooth dongle in the trunk. My experience with this has been the BT streaming directly into the DSP yields equal or better quality than what you get out of most head units. I suspect that it’s a combination of eliminating AD/DA conversions, and how mediocre most head units really are. (The head unit in my E90 is an absolute calamity.)

Then you can either run a blank plate, install gauges, or leave the factory unit intact. In fact, the Dayton will accept analogue inputs from your factory head unit, so it will even be functional!

Edit: This does, of course, require installing an amp in the trunk.
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Old 02-06-2019, 02:12 PM   #7
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Hey thanks for the recommendations! That DSP looks enticing. One thing that I don't like about the aftermarket Alpine units is that they're kind of bright which is a little annoying at night. So that's a plus for the factory HU, but I'd like HD radio, BT, and a CD player and I don't want to install a bunch of separate things. Maybe the aftermarket HU will be best then.
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Old 02-07-2019, 09:18 AM   #8
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Quote:
Originally Posted by Andrew325is View Post
Hey thanks for the recommendations! That DSP looks enticing. One thing that I don't like about the aftermarket Alpine units is that they're kind of bright which is a little annoying at night. So that's a plus for the factory HU, but I'd like HD radio, BT, and a CD player and I don't want to install a bunch of separate things. Maybe the aftermarket HU will be best then.
I currently have four of the Daytons. They are really, really good for the money. The iphone app is great, they hold their memory through battery disconnection, and the sound is good.

Pretty much unbeatable value. Literally my only complaint is that in a perfect world, they'd have 10 outputs.
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Old 02-09-2019, 05:13 PM   #9
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Awesome.

I didn't realize there's an adapter harness from BMW for the original stereo to connect a newer BMW HU like the CD43. So I'll restore the original wiring and use that. Then I can make another adapter to connect that to the aftermarket radio. That way I can switch between them as I feel like it.
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Old 02-18-2019, 09:13 PM   #10
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I wired in the original CM5908 radio and amp and it looks like the radio does need to be repaired. It hisses and crackles. The display is good though and all the buttons seem to work.
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Old 02-20-2019, 11:12 PM   #11
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Could someone help me figure out the amp bypass wiring while leaving the original wiring intact? I know, needlessly complicated.

Someone gave me a stock amp that apparently is no good, so I thought I could use it to do the amp bypass mod while leaving the wiring to the amp intact. One thing that is confusing me are the common ground speaker wires coming from the radio. I read there shouldn't be common grounds for the speakers for the aftermarket HU. So do I just connect the positive wires together inside the amp and leave the grounds connected as they are in the amp? Does the amp need to be powered on for the grounds to do whatever they need to do or should I terminate the power and remote turn on wires?

Last edited by Andrew325is; 02-21-2019 at 11:57 AM.
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Old 02-21-2019, 12:18 PM   #12
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Maybe I can install a floating ground adapter inside the amp. Except, it would be wired backwards, hmm.

Last edited by Andrew325is; 02-21-2019 at 12:31 PM.
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Old 02-21-2019, 12:52 PM   #13
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Okay, so the grounds are combined at the radio too. So the original wiring goes from common ground, then separated, to common ground at the amp, and then separated again to the speakers. Will it work if I install the floating ground adapter at the radio and then combine the grounds going to the speakers?
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Old 02-21-2019, 07:19 PM   #14
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Well forget that, haha. I’m just going to run RCAs to a new amp.
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