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      05-04-2009, 07:17 PM   #1
RAYKNLCS
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Tapping the output of the head unit

I recently bought a 4 channel amplifier that I want to use to run the 4" components and my SWS subs off of. I've read through a lot of the posts and I've seen where you can plug the balanced outputs of the radio into certain amplifiers. This is exactly what I would do, except that my amplifier has common grounds on the RCA inputs. So my question is this:

How do I take the balances output of the head unit (Professional) and convert it to common ground RCAs? Can I just use a PAC Trunk-LOC for this, or will the impedance of the LOC screw up my head unit?

Thanks for any input you can give me.

Ray
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      05-04-2009, 09:25 PM   #2
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Hey, how's it going. My name is dan, i'm actually one of the guys you were talking to earlier at columbus car audio.
I had forgotten that the new rockford fosgate power series amps have what is called a differential input rca setup, and will accept a balanced input. So, in theory you could do what you were wanting with those. I also think that the JL slash series amps are the same. What kind of 4 channel did you already get?
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      05-04-2009, 10:37 PM   #3
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I actually have two amps right now. The first one is a Kicker 750.1 and I'm pushing the 2 MTX twelves with it. I hooked it up with the Trunk-LOC on the subwoofer output of the factory amp. It's an 06 amplifier so it came out before they switched those to balanced inputs.

The new amp I recently picked up is an Oz Audio 50.4. I was hoping that it would have balanced inputs since Oz was known for making pretty high-end stuff. To my dismay when I pulled the cover off of the amp, I saw the RCA grounds connected together. I'd still like to use the amp because I got a fantastic deal on it.

I've been searching all over Bimmerpost for a month trying to find some clarification on what you can do to get around the issue of balanced versus unbalanced inputs. The only thing I have found are serveral people talking about how clean the balanced signal is and how you can plug it into a Zapco DC amp with a couple of resisters. I think my wife would shoot me if I bought an $800 amplifier!! :-)
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      05-05-2009, 11:53 AM   #4
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The way you take a balanced out and run into into a common-ground input is to use some form of converter.

Cheap converters are passive and use transformers. They usually have HORRIBLE frequency response curves, and they are usually designed for speaker-level signals, not preamp-level signals, so their internal attenuation will reduce the preamp voltage, and ruin your signal-to-noise ratio. Also, the transformers LOVE to pick up EMI out of the air and give you MORE noise.

I would include just about any passive converter made in this list. I don't know how the Jensen Transformers (different from Jensen car audio) ISO-MAX would work, but I have used it in other applications and it has worked great.

Your better bet would be to use a device with differential inputs and RCA outputs.

You can use any line driver with balanced inputs such as an Arc Audio.

You can use any Audio Control processor.

You could use a 360 from Rockford but it is way overkill unless you plan on using lots of processing options.

Use a Zapco I-Force. They are not $800.
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      08-20-2009, 09:03 AM   #5
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1) Does AuidoControl LC6i work well in balanced-to-unbalanced convertion?

2) It seems that balanced signal need 3 wires, but the HU output is only 2 wrie per channel. It is really a balanced ouput? Any way to test it, for example, RTA?
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      08-20-2009, 08:21 PM   #6
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Quote:
Originally Posted by efunroom View Post
1) Does AuidoControl LC6i work well in balanced-to-unbalanced convertion?

2) It seems that balanced signal need 3 wires, but the HU output is only 2 wrie per channel. It is really a balanced ouput? Any way to test it, for example, RTA?
1) NO. It is speaker-level to common-ground. There is an additional attenuation component.

2) Balanced is signal (+), signal (-), and reference ground. Differential inputs using RCA connectors use the RCA outer shield for signal (-).

RTA will not tell you, but I don't know that you will believe me either. You need an oscilloscope to test a signal, but to test an input, you either need to trace the PCB out and see the devices, or you need to believe the brochure.
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      08-21-2009, 10:07 AM   #7
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Quote:
Originally Posted by VP Electricity View Post
1) NO. It is speaker-level to common-ground. There is an additional attenuation component.

2) Balanced is signal (+), signal (-), and reference ground. Differential inputs using RCA connectors use the RCA outer shield for signal (-).

RTA will not tell you, but I don't know that you will believe me either. You need an oscilloscope to test a signal, but to test an input, you either need to trace the PCB out and see the devices, or you need to believe the brochure.
1)So, is there a converter for balanced-to-unbalanced only purpose? I plan to use audison LRx , but the dealer told me LRx does not accept balanced signal.

2) BMW only use two wires to transmit balanced signal. Maybe one wire is +5V, the other wire is -5V.
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      08-24-2009, 12:31 AM   #8
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I do a search, some posts said that there 2 devices will convert the balanced signal to unbalanced.

- Soundgate XR4PRO
- Peripheral SVEN4
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      08-25-2009, 02:24 PM   #9
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Quote:
Originally Posted by dvpouldar26 View Post
Can't you just tap into the powered outputs of the stock amp and run a line output converter?
No, not unless you want an equalized and crossover-filtered signal. Go read OEinterface.com.

Quote:
Originally Posted by dvpouldar26 View Post
Can't you just tap into the powered outputs of the stock amp and run a line output converter? That is what I would do and what has been done. The Peripheral converter is great. I would also check out the PAC line output converter. I have used PAC in all my installs that ive done and couldnt be happier for the price. For more channels and processing i would use the Audiocontrol LC6i. That is what many other board members have used in the past. There is also the Rockford Fosgate 360's but thats only if you want alot of adjustability and processing features.
You sound like a pro installer who has never tested the output of any of these. How do you know it's great? Ever check the freq response of any LOC? Check the pics on OEinterface.com and see the screen shots of the freq response...
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      08-25-2009, 06:51 PM   #10
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Can't you just tap into the powered outputs of the stock amp and run a line output converter? That is what I would do and what has been done. The Peripheral converter is great. I would also check out the PAC line output converter. I have used PAC in all my installs that ive done and couldnt be happier for the price. For more channels and processing i would use the Audiocontrol LC6i. That is what many other board members have used in the past. There is also the Rockford Fosgate 360's but thats only if you want alot of adjustability and processing features.
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      08-25-2009, 06:54 PM   #11
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Quote:
Originally Posted by VP Electricity View Post
No, not unless you want an equalized and crossover-filtered signal. Go read OEinterface.com.



You sound like a pro installer who has never tested the output of any of these. How do you know it's great? Ever check the freq response of any LOC? Check the pics on OEinterface.com and see the screen shots of the freq response...
I am by no means a pro car audio installer. haha. I'm just a car audio enthusiast, who has installed a few systems. I hear these products are great because the car audio shops that i have spoken with, such as Al & Ed's, use these products and reccomend some of them. I also get my info from many caraudio forums that I go on, and from the other members who have used those products, they have loved them. Thanks for the interesting info.
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      08-25-2009, 08:35 PM   #12
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Quote:
Originally Posted by VP Electricity View Post
No, not unless you want an equalized and crossover-filtered signal. Go read OEinterface.com.
Great info >> http://www.oeinterface.com/showthread.php?t=11

Now what I learned is:
1)The HU signal (HIFI option) is Balanced.
2) The HU use twisted-pair to transimit signal per channel.

But it really confused me, because balanced signal need 3 wires. How BMW use 2 wires to make balanced signal. I sent a mail to Larry to inqurie the balanced input capability of bit one, here is what he said:

"If it is 2 wires then it is NOT balanced as that does take 3 wires to be balanced. If so , no sweat just solder up some RCA s and rock and roll."
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      08-25-2009, 09:37 PM   #13
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Quote:
Originally Posted by efunroom View Post
I do a search, some posts said that there 2 devices will convert the balanced signal to unbalanced.

- Soundgate XR4PRO
- Peripheral SVEN4
You missed Soundgate LOCB.2.

The SVEN is completely passive. I don't like it and I won't use it.

The LOCB.2 I have used with good results, it is an active device that seems to work well, but it's not cheap.

No idea about the XR4PRO.
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      08-25-2009, 10:12 PM   #14
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Interesting findings:

The outputs of the head unit are isolated from the vehicle ground. Every signal in and out of that amp is internally bypassed via a 0.22uF cap to ground -- the ground leads are not tied to chassis ground, they are floating.

The E46 head does not put out ground referenced outputs - it supplies differential signal pairs that are terminated in an impedance matching network that feed an Op Amp (in the factory amp input circuitry) that is set up to remove noise induced into the lines on the way from the head to the amp in the rear. This is very good engineering - it's easier to remove the noise than to keep it out - but it does not utilize "standard" unbalanced line levels and it is not unbalanced speaker level signals

From : http://www.e46fanatics.com/faq/stereosaga.html
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      08-26-2009, 12:48 AM   #15
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Not really. You are reading too much, and E46 is way diff than E9x. You need more actual experience and knowledge gained empirically, and you need to get off the damned internet, sir
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      08-26-2009, 08:52 AM   #16
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Quote:
Originally Posted by VP Electricity View Post
Not really. You are reading too much, and E46 is way diff than E9x. You need more actual experience and knowledge gained empirically, and you need to get off the damned internet, sir

I also think so. too many infomation in internet which really make me confused. I agree with you. The more efficient way to get a clear answer is to test it myself. I'll find a local store to use oscilloscope to test the HU output. If it is a real balanced signal, then I need to find out how BMW use 2 wires to transmit it. The last thing is to test it with the bit one
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      08-28-2009, 10:05 AM   #17
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Today, I did a test in a shop. We used the HU output as the input of Audison VRx and LRx. Here is the test procedure

1) HU left front output --> VRx RCA
The VRx support balanced signal and has a special RCA. Audison call this ABS(Audison Balanced Signal). There are 3 wires in this special cable: signal+, signal-, ground. BMW HU has a 2 wires per channel output, in this case, we named it as LF+ and LF-. We connected the LF+ to signal+, LF- to signal-. Not use the the 3rd wire(ground) in ABS cable. The result was VRx worked well as it supposed to be.

2)HU left front output --> LRx RCA
LRx has a normal RCA (2 wires, signal and ground). First, we only connected LF+ to signal wire and no touch RCA ground. The speaker sounds nice. Then we connected the LF- to RCA ground, the sound is nice too and twice aloud. This prove that LRx low level input can accept the balanced signal

3)HU left front output --> LRx Speaker level input
The sound is ok but with enginee noise which did not occur in test 1&2. This means that LRx high level input can accept the balanced signal but no noise cancellation function. Seems that high level input circuit only use one signal and discard the other.

Now, I have a little question. Since LRx support balanced input, what is the benefit of VRx using ABS?

Not test the bit one since I have not got it. Based the test above, I believe its low level input also support balanced signal. Will test it when I get it.
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      08-28-2009, 11:09 AM   #18
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The audison balanced input is an interesting one, and I'm pleased to hear it works. If you're going to spend that much money, I always used Zapco and Symbilink, though, but good to know

We have other instances of amps working OK with balanced signals even though they lack true balanced inputs (such as LRx). DLS amps come to mind. The PDX amps are probably another case. These amps waste half the signal - the (-) is shunted to ground through a resistor capacitor network - but they seem to work. I don't like to recommend any amp I haven't tested in this manner in a BMW, though (I tested DLS amps on the TSX signal years ago).

There is not really any such thing as "noise cancellation function". I think what you are experiencing in #3 is that using a SPEAKER input for BALANCED signals doesn't work too well, because you are attenuating the signal - lowering its amplitude - and it's already low enough, so you make it too low and usually knock it into the noise floor. This is why I've been recommending against using Audio Control products with speaker-level inputs on balanced signals - un-needed attenuation.

But congratulations! Since you've progressed from Googling to actual testing, you have graduated from getting advice we can reasonably expect others to follow (which is never the full body of our experience) to going one step further and actually trying the installation and sharing your experiences!

No more explanations needed for you! Start that installation!
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      08-28-2009, 08:09 PM   #19
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VP, thanks for your encourage

Quote:
Originally Posted by VP Electricity View Post
The audison balanced input is an interesting one, and I'm pleased to hear it works. If you're going to spend that much money, I always used Zapco and Symbilink, though, but good to know
I know that many people are prefer Zapco Amps, but unfortunately I can not find these amps in China market. It is likely Zapco has no dealer here.


Quote:
We have other instances of amps working OK with balanced signals even though they lack true balanced inputs (such as LRx). DLS amps come to mind. The PDX amps are probably another case. These amps waste half the signal - the (-) is shunted to ground through a resistor capacitor network - but they seem to work. I don't like to recommend any amp I haven't tested in this manner in a BMW, though (I tested DLS amps on the TSX signal years ago).
Yes, I also think so. But the interesting fact is that the sound is twice aloud when I connected the LF- to the LRx RCA ground. It seems that the signal amplitude is double, which is just the working way of balanced circuit.


Quote:
There is not really any such thing as "noise cancellation function". I think what you are experiencing in #3 is that using a SPEAKER input for BALANCED signals doesn't work too well, because you are attenuating the signal - lowering its amplitude - and it's already low enough, so you make it too low and usually knock it into the noise floor. This is why I've been recommending against using Audio Control products with speaker-level inputs on balanced signals - un-needed attenuation.
I think it is the improper gain setting caused the noise. During the testing, the shop guy did not adjust the gain.

Quote:
But congratulations! Since you've progressed from Googling to actual testing, you have graduated from getting advice we can reasonably expect others to follow (which is never the full body of our experience) to going one step further and actually trying the installation and sharing your experiences!

No more explanations needed for you! Start that installation!
I learned a lot from this site and thanks all of you.
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