Hi R3V!
I got a great question on PM, so I thought I would share the question and my answer on the public forum.
Sannnie, there are so many answers to that question! Yes, if you upgraded the speakers (I have my own philosophy on that, Best Buy ain't gonna help) you will get a little better clarity and maybe a bit louder, but just a tiny bit better. However, the easiest and most impressive way to improve sound is POWER...you need an amplifier, and a subwoofer to get good sound, period. Even BMW uses amplifiers in their systems, as if you needed more evidence...right?
OK, but you want to use an amp on your stock, now WTF do you do? No worries, but put your reading glasses on!
Let me break it down like this: a deck is a deck is a deck...for the most part. You can add amplifiers, subwoofers, better speakers, whatever.
Virtually all decks use the same basic topology. There is a "tuner" (radio stage), a "transport"(CD, Cassette, whatever), a "pre-amp" and a small amplifer to run the speakers. The pre-amp stage has the volume controls, the switching from CD to Tuner, whatever other sound control functions a deck has is all in the preamp.
that Preamp in your deck is currently running a crappy little 4 watt "chip" amplifier. Very little power, poor sound quality and noisy, low performance.
The big difference in using a stock deck is this: clarity. Using a stock deck compared to a typical aftermarket deck means you will have more "hiss" and less overall sound quality.
Let me explain why!
First, there are two ways to connect an amplifier: first is "low level" and uses RCA cables, running from plugs on the back of the deck to plugs on the amp.
Decks have 1 par, 2 pair or three pair of RCAs, high voltage (4 or 5V, typically) or normal (2V), but all of them use the deck to be a "front end" only, meaning the speakers are all driven from the amplifier.
The second way to connect a deck to an amplifier is called "high level" or "speaker level input". This is what you would be doing with a normal stock deck (in this or almost any car) to get more power.
What you do in this case is one of three evils: either use a "line output converter" (LOC) or use "high level" inputs.
There are a few LOCs that are substantially better than others, we will get into that in a few.
Here is the big drawback to using the stock deck: when you connect an amplifier to a deck, whatever noise or distortion is made by the deck (and ALL electronics have noise and distortion, don't kid yourself) is amplified by the amplifier.
The stock deck uses a puny little "chip amp" inside the deck to run the speakers. Because it makes so little power and because its just a deck, that little chip amp (4 watts per channel yay!) is noisy as fuck, terrible distortion levels and just generally sucks.
So, as bad as that stock deck is, when you send that signal to an amplifier, it only gets worse! Whatever is sent to that amplifier is amplified, so if send it 1% distortion, you might get back 10% THD....kinda sucks! Now you have amplified noise and amplified distortion so no matter what you do, you still get noise.
BTW, I should point out that the "noise" I am referring to is not alternator whine, static or pops and clicks, but just simple background noise, more of an annoying "hiss" than anything. When you see the "Signal to Noise" (S/N) ratio on anything electronic, that is what is referred to as noise. The higher the number the better.
So now, lets talk about how to get better sound out of that stock deck!
First, any car audio nut will tell you that all good systems have a subwoofer...but if you ask little old ladies in a grocery store parking lot if the radio in their car sounds good, you will find that all of them have a subwoofer in their stock system, even in Camrys and Grand Caravans, all of them use amplifiers and subwoofers in their deluxe systems, so just expect that you will need one too. Just like those little old ladies that have no clue that their stock MDX system has a subwoofer, it need not be huge, giant booming bass...just something to allow the midrange speakers to not try to produce bass. When your main speakers attempt to produce bass, they flap around and ruin the clarity of the midrange. This is what "crossovers" do, is filter the signal to the speaker so that particular speaker can perform at its best.
Using a series of filters called "High Pass" and "Low Pass" both before and after the amplifier (built in to the amp, generally) are what makes for a great sounding system. I am more than happy to help you through setting all of this up, it really is not hard. Several dozen people have done beautiful installs on this board alone, you can too.
Of course, we at GAS make several different boxes for several different BMW chassis, but that is not the point here. The fact is that if you want a great sounding car, adding a subwoofer is a necessity, even if it is only a single 8".
Enough about subwoofers though, lets talk about the interface between the stock deck and the amplifier.
We are going to toss out three options here. All of them are applicable to all BMWs, but with the added twist of using the stock indash fader instead of just using the speaker wires from the deck.
First choice in how to do this is use the 4 positive wires from the fader or deck as the center pins of RCAs while using chassis ground as the outer shield. This is the cleanest, lowest distortion, lowest cost, easiest and best method possible, but it seems to confound many people, and it does not work with all amplifiers, but it does work with most decent amps.
This can be done easily behind the deck, and RCA cables ran from behind the deck to the trunk, along with a subwoofer level control cable. IMO, this is the smartest way to do this, so you could easily swap to an aftermarket deck.
This same process can also be done at the stock amplifier location, all the needed wiring is already there on Premium Sound cars, even the early ones, including E24 and E28.
How this connection is done is simple, all you need is $5 worth of parts from Radio Shack:

Very simply, from the back of the fader you would use the blue/red to the center pin of one jack, blue/black to another, yellow/red to a third and finally, yellow/black to the fourth.
All 4 plugs would need a chassis ground, use the brown/black already in the harness. Solder a length of wire to each, its all simple stuff.
Whatever amplifier you choose should have the ability of accepting a 6V input, it is safe to say that 95% of all car audio amps made in the last 10 years will work perfectly, but I am offering no guarantees here.
Second choice is the dreaded LOC. This noisy little pile of crap is made by dozens of companies and uses a series of resistors and inductors to drop the speaker level signal to typical 2V RCA levels. The problem with these is that when you just restrict a signal like these do, the sound quality is drastically reduced. I hate these miserable things and do my best to help people find a way around them...but the fact is that they do work.
The classic example of this is the SOEM-4, feel free to go look it up.
Third method is much more expensive and significantly harder to set up, but offers drastically better performance, and that is an "Active" LOC such as the JL Audio "Cleansweep" or the Audiocontrol "LC" (LC2, LC6, LC7, LC8)series.
Her is an LC8iinstalled in an E39:

There are several o the market, most are well over $200 and all do a great job of making a stock deck interface with aftermarket amps. Most offer the advantage of making a subwoofer output for you, some include a sub level control as well, but choosing a correct amplifier for your needs will get around that issue as well.
The fourth option is coming sooner rather than later, and that is a heavily modified stock deck from us here at G.A.S. We will be adding a bluetooth module and bypassing the chip amp to get a true pre-amp level signal, so you can have an absolutely stock looking interior while having modern features like hands-free calling and bluetooth audio...so, all that being said, I hope all of this information is useful and let me know if I can help.
Luke
I got a great question on PM, so I thought I would share the question and my answer on the public forum.
Originally posted by Eufonik
OK, but you want to use an amp on your stock, now WTF do you do? No worries, but put your reading glasses on!
Let me break it down like this: a deck is a deck is a deck...for the most part. You can add amplifiers, subwoofers, better speakers, whatever.
Virtually all decks use the same basic topology. There is a "tuner" (radio stage), a "transport"(CD, Cassette, whatever), a "pre-amp" and a small amplifer to run the speakers. The pre-amp stage has the volume controls, the switching from CD to Tuner, whatever other sound control functions a deck has is all in the preamp.
that Preamp in your deck is currently running a crappy little 4 watt "chip" amplifier. Very little power, poor sound quality and noisy, low performance.
The big difference in using a stock deck is this: clarity. Using a stock deck compared to a typical aftermarket deck means you will have more "hiss" and less overall sound quality.
Let me explain why!
First, there are two ways to connect an amplifier: first is "low level" and uses RCA cables, running from plugs on the back of the deck to plugs on the amp.
Decks have 1 par, 2 pair or three pair of RCAs, high voltage (4 or 5V, typically) or normal (2V), but all of them use the deck to be a "front end" only, meaning the speakers are all driven from the amplifier.
The second way to connect a deck to an amplifier is called "high level" or "speaker level input". This is what you would be doing with a normal stock deck (in this or almost any car) to get more power.
What you do in this case is one of three evils: either use a "line output converter" (LOC) or use "high level" inputs.
There are a few LOCs that are substantially better than others, we will get into that in a few.
Here is the big drawback to using the stock deck: when you connect an amplifier to a deck, whatever noise or distortion is made by the deck (and ALL electronics have noise and distortion, don't kid yourself) is amplified by the amplifier.
The stock deck uses a puny little "chip amp" inside the deck to run the speakers. Because it makes so little power and because its just a deck, that little chip amp (4 watts per channel yay!) is noisy as fuck, terrible distortion levels and just generally sucks.
So, as bad as that stock deck is, when you send that signal to an amplifier, it only gets worse! Whatever is sent to that amplifier is amplified, so if send it 1% distortion, you might get back 10% THD....kinda sucks! Now you have amplified noise and amplified distortion so no matter what you do, you still get noise.
BTW, I should point out that the "noise" I am referring to is not alternator whine, static or pops and clicks, but just simple background noise, more of an annoying "hiss" than anything. When you see the "Signal to Noise" (S/N) ratio on anything electronic, that is what is referred to as noise. The higher the number the better.
So now, lets talk about how to get better sound out of that stock deck!
First, any car audio nut will tell you that all good systems have a subwoofer...but if you ask little old ladies in a grocery store parking lot if the radio in their car sounds good, you will find that all of them have a subwoofer in their stock system, even in Camrys and Grand Caravans, all of them use amplifiers and subwoofers in their deluxe systems, so just expect that you will need one too. Just like those little old ladies that have no clue that their stock MDX system has a subwoofer, it need not be huge, giant booming bass...just something to allow the midrange speakers to not try to produce bass. When your main speakers attempt to produce bass, they flap around and ruin the clarity of the midrange. This is what "crossovers" do, is filter the signal to the speaker so that particular speaker can perform at its best.
Using a series of filters called "High Pass" and "Low Pass" both before and after the amplifier (built in to the amp, generally) are what makes for a great sounding system. I am more than happy to help you through setting all of this up, it really is not hard. Several dozen people have done beautiful installs on this board alone, you can too.
Of course, we at GAS make several different boxes for several different BMW chassis, but that is not the point here. The fact is that if you want a great sounding car, adding a subwoofer is a necessity, even if it is only a single 8".
Enough about subwoofers though, lets talk about the interface between the stock deck and the amplifier.
We are going to toss out three options here. All of them are applicable to all BMWs, but with the added twist of using the stock indash fader instead of just using the speaker wires from the deck.
First choice in how to do this is use the 4 positive wires from the fader or deck as the center pins of RCAs while using chassis ground as the outer shield. This is the cleanest, lowest distortion, lowest cost, easiest and best method possible, but it seems to confound many people, and it does not work with all amplifiers, but it does work with most decent amps.
This can be done easily behind the deck, and RCA cables ran from behind the deck to the trunk, along with a subwoofer level control cable. IMO, this is the smartest way to do this, so you could easily swap to an aftermarket deck.
This same process can also be done at the stock amplifier location, all the needed wiring is already there on Premium Sound cars, even the early ones, including E24 and E28.
How this connection is done is simple, all you need is $5 worth of parts from Radio Shack:

Very simply, from the back of the fader you would use the blue/red to the center pin of one jack, blue/black to another, yellow/red to a third and finally, yellow/black to the fourth.
All 4 plugs would need a chassis ground, use the brown/black already in the harness. Solder a length of wire to each, its all simple stuff.
Whatever amplifier you choose should have the ability of accepting a 6V input, it is safe to say that 95% of all car audio amps made in the last 10 years will work perfectly, but I am offering no guarantees here.
Second choice is the dreaded LOC. This noisy little pile of crap is made by dozens of companies and uses a series of resistors and inductors to drop the speaker level signal to typical 2V RCA levels. The problem with these is that when you just restrict a signal like these do, the sound quality is drastically reduced. I hate these miserable things and do my best to help people find a way around them...but the fact is that they do work.
The classic example of this is the SOEM-4, feel free to go look it up.
Third method is much more expensive and significantly harder to set up, but offers drastically better performance, and that is an "Active" LOC such as the JL Audio "Cleansweep" or the Audiocontrol "LC" (LC2, LC6, LC7, LC8)series.
Her is an LC8iinstalled in an E39:

There are several o the market, most are well over $200 and all do a great job of making a stock deck interface with aftermarket amps. Most offer the advantage of making a subwoofer output for you, some include a sub level control as well, but choosing a correct amplifier for your needs will get around that issue as well.
The fourth option is coming sooner rather than later, and that is a heavily modified stock deck from us here at G.A.S. We will be adding a bluetooth module and bypassing the chip amp to get a true pre-amp level signal, so you can have an absolutely stock looking interior while having modern features like hands-free calling and bluetooth audio...so, all that being said, I hope all of this information is useful and let me know if I can help.
Luke