High (Speaker) v. Low level inputs on Amp

I suspect this is a newbie question, but I did do a search on this forum and couldn't find anything directly on point so here it goes -- thanks in advance for any suggestions.

I have a 2004 Honda Accord with Nav. system -- I have already upgraded the speakers to Boston Acoustics Pro components in front and SL95 6x9s in the rear (sweet!).  I am planning on having my audio dealer install an Alpine MRP-F240 (4 channel) amp between the factory head unit and the speakers.  This amp comes with BOTH RCA and speaker level inputs.  I understand that the factory head unit does not have RCA preamp outputs, so I have to work with the speaker-level outputs on the head unit.  The amplifier will likely be located in my trunk.

Here's the issue -- my dealer is telling me that, instead of simply wiring the speaker level outputs on the head unit to the speaker level inputs on the amp, I should pay $140.00 for two sets ($69.95 each) of Monster Cable FX100 cables to "downconvert" (my term) the signal to a low level RCA signal and use that to connect to the amp.  I would like to be able to discuss this issue intelligently with the dealer -- here are my questions:

1.  If the signal is already at speaker level coming out of the head unit, is there any legitimate reason to bring the signal down to the RCA level just to connect to the low level plugs?  I understand that, if I had RCA outputs from my head unit, it would be better to connect to the amp through the RCA jacks, but I dont understand the point of doing this is the signal is already at speaker level (with whatever inherent distortion exists).  BTW, you can assume I would use high quality speaker wire and power cables, and there currently is no noise or hissing in the system.

2.  If these are requiRED / strongly recommended, are there any less expensive alternatives?

Thanks again.

In my experience, there is NO problem using high-level inputs on good quality amps like your Alpine.  There is no legitimate electrical reason to convert the speaker level signals to line level (which, by the way, cannot be done using Monster Cables alone.  Another component called a line-out converter is needed.)   When adding an amp to a factory system, running speaker level feeds from the OEM output to the speaker-level inputs of the amp is probably the cleanest way to go as well, since you will not add an additional possible noise source: the LOC.

For this install, there is no need to convert to line level, IMNSHO.  For future reference, a cheaper alternative to Monster Cable for good quality signal cables is KnuKoncepts or Stinger.  Monster is good, but you pay more for the brand name.

Cheers!

You can go either way, if you are going to be replacing the factory head unit with an aftermarket I would try the built in adaptors first. If they work good, then leave them alone. They generally work very good for most applications and can handle most if not all factory head units. Where they may run into a problem is if the system uses a hidden amplifier, if it does it may send too powerful signal into the amp and distort the input stage. In this case an outboard LOC that takes a high power input works best. Some of these units also have a gain setting on them. $140.00 on "special" adaptors is way too much compared to the other alternative.

Personally I would not use either, I would use an outboard processor that does the same thing but provides much more control of the system. Audio Control makes a good adaptor for just this reason, have a look at their website, www.audiocontrol.com and in particular the EQS model. This is much more expensive than the adaptors that they mention but will do a way superior job at the input and conversion of the signal, manipulation of the signal (equalization), a line driver for better use of your amplifiers. It may also be used if and when you upgrade the factory head unit.

Years ago before amplifier's had high level inputs I used the line out convertors but put them back by the amp instead of by the radio. By doing it this way, I was running a hotter signal to the amp location and there was less chance of noise in the system from the cable runs. If I ran the convertor behind the radio, the lower level RCA's that went to the amp had more chances for picking up noise. Also with the adjustable line out back by the amp, it's easier to adjust and you don't have to pull the radio out of the dash to access it. If you get a different amp that requires a different input level, the LOC is right there and easy to get at without pulling out the radio again.

If you add an amp to the factory radio and to the factory location speakers, order and buy the male and female radio harness adaptors. One plug will go into the radio and the other into the car harness. Extend the speaker wires off of the radio to the amp location and also do the same for the speaker wires off tof the factory harness side. This way you do not have to cut any wire and it's pretty much a plug and play setup. Aamp of America sells 9 conductor wire just for this application (8 speaker wires/one turn-on wire).

Later when you go to sell the car, take out the factory radio, unplug these two harness adaptors, plug the factory end back into the radio and the stock system works. Quick and simple.

The only problem (but it's just some parts) is that the LOC's have female ends so you have to run short male to male cables between it and the amp's input.

Jim/Saint Louis  

DYohn and Rob@Forbidden --

Thanks folks for the quick replies.  What you are saying makes a lot of sense and reinforces my thoughts as well, particularly the point about giving it a try before I sink a lot of money into cables and converters.  I believe my head unit is essentially the same unit Honda uses on all of its Accord models (other than the EX Coupe, which comes with more power), so I doubt overpowering the amp will be a problem, but I will definitely keep that in mind.  DYohn, the Monster Cable FX100s are line output converters I believe (one end is speaker connectors, the other end are RCA connectors with adaptors and filters in between), although I would still need to add extra lengths of RCA cable -- more $$.  Forbidden, thanks for the alternatives as well, and I have bookmarked the site for future reference, but that's a bit much for me at this point.

CustomJim --

Thanks as well -- I am actually having an installer do the work, and I will mention youre point to see how much more it would cost to do that way.  Chances are I would likely sell the system with the car anyways.  That way I can get a new one every few years, and this car is likely to go to my daughter when she is old enough to drive.

Rich

RichmondR wrote:

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CustomJim --

Thanks as well -- I am actually having an installer do the work, and I will mention youre point to see how much more it would cost to do that way.  Chances are I would likely sell the system with the car anyways.  That way I can get a new one every few years, and this car is likely to go to my daughter when she is old enough to drive.

Rich

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Rich,

The reason I'm suggesting having it done with harness adaptors is it is a new car and let's say there is a problem with the car and the dealership gets huffy and say's it's from the stereo or if there is some kind of recall to where they have to replace an existing harbness in the car. The harness adaptors involve NO cutting of the wiring and the stuff you or another shop installs can be unplugged and put back exactly like how the factory had it. I just don't want to see you getting burnt from an improper install or have some kind of goofy problem arise later.

Jim 

Rich,

I just prchased a 2004 Accord LX and would like to mount Boston Accoustic Pro  component speakers in it as you did.  Can you tell me where you mounted the crossovers and tweeters?  What did you do about the in-dash tweeters?  At what point in the car wiring harness did you wire to the crossovers?  Did you snake your wiring to the door through the factory harness?  Any help you can provide would be greatly appreciated.

Thanks, John

custom jim, if RichmondR wanted to get an aftermarket head-unit and his rca cables are in back are by the LOC that gets its signal off of the rear speakers he will have to run rca cables again to the front of his car. This would be annoying, that is why its better to just connect the LOC behind the radio so you dont have to run another set of rca cables if he gets a new head-unit. Also he shouldn't have a problem with noise as long as he gets a good set of rca cables from someone like Stinger. Monster Cable is completely over priced. You can buy something alot cheaper and get the same quality.

jfay6 I would run new lengths of speaker wire if you have a set of components. I would mount the crossover under the seat(dont mount it in the door because it gets too hot in there and because of moisture) and run the new length of wire from there to the amplifier or head-unit from there. Then run two sets of speaker cable, one for the Boston tweeter and the other to the woofer. You can run the wires to the speakers from the crossover through the locations that the factory speaker cable runs. The factory tweeters are probobly wired in paralell with the factory woofer so you will have to find where it joins the factory woofer wire. I wouldn't incorporate the factory tweeters into your system because the Boston tweeters will be much better and it can cause cancellation if you have two sets of tweeters running.

customsuburb, if RichmondR wants to get an aftermarket radio later then I would have the RCA's run but not hooked up to anything while I ran the other wiring. What would be annoying is having to do more work than what is needed by adding an external LOC and RCA cables to an amp he says has high level inputs and a radio that he says has speaker level outputs. I was not assuming he would upgrade his radio but if he was then I would just run the RCA's so they were in place for later but for now run the radio's speaker level outputs to the amplifier's hi-level inputs. If he was not going to upgrade later I would extend the speaker wires off of the radio and put the LOC in back as it's less problems that could arise later.

Custom Jim

I would really suggest using an LOC behind the radio and using an external crossover/line driver(like AudioControl's 24XS) in the trunk if you're worried about the voltage of your preamp outputs. This would give you superior sound over the high level inputs on the amp and more control over the signal also. You could also use this to improve the sound when you buy an aftermarket head-unit.

If you were going to run rca cables to the factory head-unit why not just use them with an external LOC behind the radio anyway. If he buys another amp he shouldn't have to adjust the LOC either. They usually output around 4 volts, all he would need to adjust is his gain on his new amplifier(it isn't like he is going to have his gain all the way up just because he bought a new amp).

customsuburb wrote:

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Custom Jim, I would really suggest using an LOC behind the radio and using an external crossover/line driver(like AudioControl's 24XS) in the trunk if you're worried about the voltage of your preamp outputs. This would give you superior sound over the high level inputs on the amp and more control over the signal also. You could also use this to improve the sound when you buy an aftermarket head-unit.

If you were going to run rca cables to the factory head-unit why not just use them with an external LOC behind the radio anyway. If he buys another amp he shouldn't have to adjust the LOC either. They usually output around 4 volts, all he would need to adjust is his gain on his new amplifier(it isn't like he is going to have his gain all the way up just because he bought a new amp).

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If I had a radio that did not have pre-amp outputs and wanted to wire it to an amplifier that had RCA and line level inputs I would wire it up using the high level inputs and allow the internal LOC inside the amp to do it's thing. If it works and performs like it should then were done. I have no need to add or spend any more money on external LOC's, RCA cables, or processors from other companies.

If later I change just my amplifier to one that only has RCA inputs then I would place the external LOC back by the amplifier and not have the added expense of long RCA cables going from the front to the back of the car and by doing it this way I'm not having to pull the radio back out again and another thing is if it's an adjustable LOC those controls are easily adjusted should any other amp be used later. With long RCA cables being run here I would have a greater chance of noise being induced into the cabling vs the shorter ones from the LOC to the amp with the LOC by the amp and not up front.

If even later I then changed the radio to one that has RCA output's THEN I would take out the LOC and run the RCA cables from the radio to the amp.

If the radio did not have enough signal coming out of it then I would put the line driver up front behind the radio so the low level cabling is kept as short as possible.  

I just think RichmondR needs to see how it works by hooking up his radio to his 4 channel amp the easiest way possible with the least amount of parts and without having to use external LOC, front to rear RCA cables or anything else. If it works and performs without these things, great. Time for a beer.

RicmondR, Here is my suggestions. Try having it wired with the speaker wires off of the radio to the high level inputs of the amplifier. If it works, your done. If for some reason they find out the radio has too much signal output for the amplifier's input, then have them install a LOC in the area that the amp is located. If they find out the radio does not have enough signal out of it, then have a line driver installed behind the radio. You just want the least amount or length of small signal between the radio and the amplifier. 

If you do replace your factory radio get one with a higher output pre-amp voltage and then run RCA's directly to the amp you have.

If later I change just my amplifier to one that only has RCA inputs then I would place the external LOC back by the amplifier and not have the added expense of long RCA cables going from the front to the back of the car and by doing it this way I'm not having to pull the radio back out again and another thing is if it's an adjustable LOC those controls are easily adjusted should any other amp be used later. With long RCA cables being run here I would have a greater chance of noise being induced into the cabling vs the shorter ones from the LOC to the amp with the LOC by the amp and not up front.

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If all you are trying to do is save money on rca cables by putting your LOC in back you arn't going to save much. For instance Streetwires Zero Noise 2 6.5' cable is $17 compared to the same type of cable that is $22 and 16.4' long. You also should not have noise problems as long as you dont route your rca cable right next to your power cable or with the brake light cable. Finally, YOU should not have to adjust your LOC every time you buy a new amp. Besides if you use rca cables and an LOC you won't have to worry about the amp's internal LOC not producing satisfactory sound. If he was running subs I would use the internal LOC on the amp because you can't really hear a difference with the lows, but he is running some high quality speakers so why not just go with the best sounding option, the LOC, which is usually your best way to go.