I know the topic of tapping the signal before or after that amp has been discussed many times before. However, I am going in for some upgrades to my current audio system which will include a Bit One or TenD (depending which route I take). As it stands right now, my signal is tapped before the amp, spliced to rcas and sent to a JL Audio HD900/5. It sounds ok but not great, it's very harsh and needs some tuning. The installer I'm working swears by taking the signal after the factory amp, so much so that he wants to put mine back together just to take the signal after. He says that he's done it before on this vehicle and it sounds great. http://www.soundauto.net/Photo_Galle...Acura_MDX.html

Just wondering what is the best way to go and why? Like I said before, I've always heard before the amp but never knew the reason why. Thx in advance!

 

Try it both ways and see for yourself. You may like it after the stock amp. Some people talk about noise after the stock amp but I didn't experience any.... I did when taking pre-amp signal before hooking up a line driver with balanced differential input.

If you decide to try pre-amp I urge you to take advantage of the differntial balanced output of the head unit as it really does eliminate noise from the signal. My line driver is connected in the trunk and my unshielded .3-.8v signal from the head unit is going through all sorts of electrical fields on the way to the line driver unit...... doesn't matter because it is all eliminated due to having the proper circuit topology.

 

It is easier for a shop to tap into a high level signal and then depend upon the processor to be able to eliminate the garbage that the OEM amp has created. That is one reason why most shops will insist on going post amp....so they can sell you a processor.

It makes the most sense to always take the cleanest signal that you have available to work with and that would be pre amp. use that signal and then you can use the processor to its full value instead of depending on it to clean up a dirty signal that you did not have to dirty up in the first place.

OH NO......circuit topology? that is what has eliminated you noise?

 

Only a very weak system will not have the hiss. The stock amp has a high noise floor (the hiss). When you amplify after the stock amp you're amplifying it's high noise floor along with the music.

That 900/5 is more than powerful enough to show the hiss of the stock amp. Using processing to get rid of the hiss will severely limit the system's upper end response.

It's easier for the shop to install, that's the only reason I can think they would want to go pre amp.

The only way to not have hiss post amp is to dial back the amp's gain and by the time it's turned down enough to where you don't hear the hiss, it's just barely louder than stock.

Last, be careful who you take advice from, "circuit topology" does not reduce the noise. You don't need "balanced differential" (the TL does not use true balanced differential outputs). I've run my nearly 20yr old McIntosh amp, a cheap Interfire amp, and many in between in this car and there's no difference other than the amp's noise floor.

A line driver is used if noise is picked up during the signal's trip to the amp in the trunk or to boost the signal if it's too low for the amp. A line driver boosts the signal so the amp does not amplify as much and any noise picked up is reduced. If you think about this for a second you can see how completely useless a line driver is when installed in the trunk for noise that's picked up along the way. In the trunk it's only good for amplifying the signal but no noise reduction.

Mounting the line driver up front near the head unit is the only way it will reduce noise that's picked up along the way. You're amplifying the good signal for it's journey to the amp. This improves the signal to noise ratio since the amp gain won't have to be turned up as much with the hotter signal meaning the noise won't be amplified as much.

 

Yeah forget those guys and pick up a JL RLC-LD to hook up preamp. You will forget about 'noise' and 'hiss'.

 

Do you know what a line driver does? You're telling him to waste money on something that can't possibly work. The stock amp produces hiss. It's there when the system is bone stock. You can't hear it when stock because it doesn't go loud enough. When you amplify hiss there is no getting rid of it. You can waste your money on the most expensive components and it will make zero difference. A line driver does not remove hiss. Throwing money at stuff does not fix everything. You need to focus more on install instead of money. Make the signal runs pre amp away from power and ground. If you must use a line driver install it up front.

 

Sigh... again if you utilize the balanced differential signal with a unit that can convert balanced differential signals it does not matter if you pass the signals through a reactor core (assuming the wires could withstand the heat).
Here I have copy / pasted how this works for the benefit of yourself and others:

"Glossary Definition for differential-signal

Glossary Term:differential-signal

DefinitionMost electrical signals are single-ended, comprised of a single wire and ground. Differential signals use two wires which are the inverse of each other -- when one swings positive, the other swings negative in equal magnitude. The receiving circuit looks only at the difference between the two, ignoring any common-mode voltage. This "push-pull" arrangement reduces the impact of electrical interference because external noise will affect both wires equally and the common-mode rejection will ignore the noise.Examples: RS-422, RS-485, professional audio signal standards (especially for microphones), the signal lines employed by Ethernet, and the standard twisted-pair analog telephone (POTS) line."

This definition fails to mention that a balanced differential signal like we have in our TLs effectively doubles when converted to an unbalanced signal in the receiving unit (JL RLC-LD or any other device with (you following Jim?) the correct circuit topology). Just trust me or look it up.

Edit: for those who are catching on the effective HU signal voltage is closer to 1.6v when utilizing the optimal circuitry.

 

You could have saved some trouble if you realized stock does not use true balanced diff.

 

Am I the only one who has ever realized this guy knows absolutely shyt?

 

Steve, what's the problem????

I don't see where I hate cars is doing anything wrong here. You have your opinion, he has his opinion.

There is no name calling. This has not escalated into a shouting match or cussing.

If you can't have a gentlemanly "back and forth" about this subject, then don't continue to argue your side. Frankly, I don't see anything wrong with anything you two have posted.

I'm not a technical person when it comes to electronics, but I can see both sides of this conversation.


Guys, keep it clean, don't name call or make it personal. Continue to make your points. I'm sure that the OP (BlueAC) is getting more information than he ever excepted.

 

Yup you proved me wrong. Show me that stock uses true balanced differential. I'll give you the next 9 hours to try. When I get home I'll provide you with the necessary links to show I'm right.

As I've said, I've run my near 20yr old McIntosh from the HU, no noise. I've run many amps, no noise. The line driver can get rid of noise by boosting the signal BEFORE it begins it's journey to the trunk. Putting it in the trunk will only boost the signal, it won't help with noise.

 

I have no interest in spending nine hours trying to teach you about our particular balanced differential signal. I have much better things to do.

I never said you couldn't run a line driver close to the head unit . I am saying it is better to utilize the noise cancelling feature in our signal that our head unit employs. The method I prescribe doubles the signal to noise ratio and eliminates nearly all electrical interference if the converting device (JL RLC-LD) is introduced after the run to the amplifier (s). The method you prescribe is also effective but my method in this particular case is cheaper, easier, and makes more sense given the type of signal we are trying to work with in our HUs.

 

so we should use an unshielded cable and run it past several power lines to a line driver mounted in the trunk to then again amplify the now dirty signal to feed to our amps? And somehow thats your argument for how to set up a system? pointless and just plain bad advice. is that somehow the topology your referring to now? I think you should stick to tuning by application of vinyl protectants like you prescribed previously.

the noise cancelling feature that our head unit employs? seriously? there is certainly some noise canceling that I would love to see employed, but its in your head, not in my HU. please do not continue to generate completely false and erroneous information that others may interpret to be correct.

 

I prefer preamp. The signal is less manipulated that way. Otherwise you get the processing in the stock amp, then the processing to correct what the stock amp does, then the processing to correct for the acoustics of the car. (technically the electrical correction and the acoustic correction would be done in the same step. You are just having to correct 2 problems.) Going preamp, you have to correct for the slight dip at 1k and then for the acoustics of the car. I have always been a fan of using as little processing as possible to achieve the desired results.

Plus, the HD900/5 will take all the way down to an 800mV input so you don't need some massive signal to run the thing (although most processors do include a line driver section).

Also, I always get a kick out of the "run the signal away from the power" concept. All of the DC in the car is one big loop. The entire chassis ground is the path for all the DC voltage running through the car. So, if you run the signal cable anywhere near any metal in the car you are running it near DC flow. That is why a shielded cable is preferred in an automotive environment. As long as you use a nicely shielded cable, and have adequate ground connections you can run wires however you want. (barring coiling up excess signal cable creating an RF antenna). Granted I usually do run them on opposing sides, but it is because it gets really tricky to hide 4ga (or bigger) power, 1-4 sets of signal cable, and speaker cables under the carpet in one big bunch.

 

I have no interest in spending nine hours trying to teach you (again) about our particular balanced differential signal but I will spend another five.
Our signal consists of two polar opposite but otherwise identical signals. The reason for this is when using the correct receiving device the circuit will take whatever is in common to the two signals and send that to ground. Remember the two signals are polar opposites but whatever electrical interference is common to both signals will be rejected by the circuit. This method is not perfect but if you use twisted RCAs it is very close. In fact the best method (however unnecessary) would be to connect the balanced differential input line driver as close the head unit as possible as you have done with your unbalanced line driver.

I never said you couldn't run a line driver close to the head unit . I am saying it is better to utilize the noise cancelling feature in our signal that our head unit employs. The method I prescribe doubles the signal to noise ratio and eliminates nearly all electrical interference if the converting device (JL RLC-LD) is introduced after the run to the amplifier (s). The method you prescribe is also effective but my method in this particular case is cheaper, easier, and makes more sense given the type of signal we are trying to work with in our HUs.

Do not waste your time trying to prove me wrong because you will simply resort to rhetoric as before. It is in your stubborn nature. Perhaps we are too similar in that regard and why we clash so badly. Anyway I just want the facts to be straight since this forum is about finding the best methods to improve our cars.

Have a good day.

Tell you what if you still need me to prove /explain something after I will get out the laptop so I am not condensing everything.

I noticed the slight dip at 1k. Whats thereason for that? (So it is not my drivers fault)

 

IHC are you talking true 3 pin balanced or simply The positive and negative having opposite phase with no common reference ground? The wiring simply doesn't exist for the first, but it was my understanding that the TL used the 2nd. Or at least I had signal issues with the amp until I got something that could handle balanced (yah, not true balanced) input.

I've never seen tech docs one way or the other or had someone put it on a scope that I've heard of. However I know this argument has been had on the board many a time with one person insisting on balanced input requiring 3 wires.

 

It's just in the signal coming out of the headunit. Don't know why they did that. It could have to do with equal loudness curves, but if they did that I would think there would be more done. Also, with the processing that is done in the amp I would assume any thoughts on that level would be addressed in the amp. More than likely they saw the pre-amp output and said, "eh, good enough."

 

Dancing around the facts again. You absolutely won't get into a technical discussion. You have 8 hours to google your answers. I'm going to call you on your nonsense until you understand that you will either have to stop lying or you need to move on.

3 pin balanced. I was wanting to see how long it would take him to google it.

 

Ok thanks for all the info. I think I'm just going to have the installer leave the signal path as is and place the processor before the factory amp. I will report back once I make my decision on the processor and get it all installed.

 

Good luck with it. Nice car by the way!

 

Hmm so are you saying its impossible to get any noise from the cars electrical system even if I run my RCAs along side 2ga power wire which happen to be feeding class d "switching" amps in the trunk?

 

Not saying impossible. Poor grounds, RF interference, and faulty equipment can all cause noise issues. What I'm saying is whether you run signal cables directly next to power lines or have them on opposite sides of the car but are running them along the chassis you are running them along the path of DC current flow, so don't stress about it for that reason.

As long as you use a properly shielded cable there should be no difference as long as everything else is up to snuff.