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Car Stereo Pit Fall #1 - Never Use Speaker Level Input on Amplifier

Simply put, always use the preamp output on the head unit to connect to the preamp input on the amplifier. I have always followed that rule when I put in a new car stereo system into my cars, except one time. That is when I learned the lesson the hard way.

When I bought my 2001 Subaru Impreza 2.5RS, I decided to hold off putting in a custom head-unit because it came with a premium stereo system. Even though the premium stereo system came with a under driver seat subwoofer, it's far too small for my take. It just didn't move enough air to produce the punch I'm after. So I installed my Kenwood KSC-W800 Subwoofer with the Profile California amplifier.

The built-in head-unit does not have preamp out. Fortunately (or so I thought), the Profile California amplifier accepts speaker-level input. It's a feature that most car stereo amplifiers on the market have today.

So I did not pull the RCA preamp cable from the head-unit to the trunk. In hindsight, that was a mistake. Because when I finally did put in a custom head-unit with preamp out, I was too lazy to pull the RCA preamp cable. After all, the speaker-level input has worked so well for years. And for 7 years, I enjoyed listening to the stereo in that manner.

Just a few days ago, while driving along, the stereo stopped producing any sound. After tracing through the system, I found that the speaker connectors board on the rear passenger speaker has came loose. It just dangled from the speaker. And apparently, it came in contact with the metal parts of the speaker chassis (ground). After gluing the board back, I powered up the stereo and was happy to get sound. But what happened to the base?

I went back to the trunk and noticed that the amplifier wasn't working like it normally would. I swapped the subwoofer/amplifier unit with the one in my wife's vehicle (they are built the same way) and hers worked just fine. Oh oh . . . it seems that the short to ground has burned out some circuitry on the amplifier. Even the RCA preamp input no longer works.

After doing a search on the Internet, I notice that shorting to ground while using the speaker-level input is a common cause of amplifier damage. Using the preamp connection protects the amplifier in that manner. I should have use the preamp connection from the start. Meaning I should also have ditched the stock head-unit for a custom one from the beginning as well. That's a hard lesson learned. Now I got to find a replacement amplifier for my set up to replace an amplifier that served me well and reliably over the years.

Chieh Cheng
Tue, 18 Mar 2008 08:53:06 +0000

I just ordered a new Profile California AP400 from Crutchfield. It's a 2-channel amplifier that can be bridged to a mono output. Pretty much like my older Profile California model. It's about the same small size too, so it should be a good replacement. I'll let you know how it goes when the unit arrives.

P.S. If you want to get $20 off your first-time $200 order at Crutchfield, you can use this referral code: p2e1e-h48g1-iqcct

Chieh Cheng
Tue, 18 Mar 2008 17:59:23 +0000

I have gotten the Profile California AP400 several weeks ago and installed it. It's working well. What surprised me is that rather than include an integrated line level converter in the amp, Profile packaged a separate external line level converter (see photo below). I guess this way, if you burn out the line level converter, your amp still works.

Knowing this, it was tempting for me to continue the line level converter input. But I finally decided against it. Instead, I finally pulled the RCA preamp cable through my car.

Attached Image:

Line Level Converter.jpg

Chieh Cheng
Mon, 14 Apr 2008 21:36:47 +0000

can i just say.... if your wiring is decent enough, this whole thing shouldnt be an issue... and there are forms of protection that can be used...

Steve Clack
Sat, 17 Apr 2010 11:13:39 +0000

Did you find any sound improvement after changing to Preamp out instead of using speaker level?

Kwok
Sat, 22 May 2010 07:46:34 +0000

I think it was about the same. I didn't really analyze for any difference. Theoretically the pre-amp connection should be cleaner. In this instance, the theory is good enough for me.

Chieh Cheng
Sun, 23 May 2010 05:21:48 +0000

I found that even with high quality rca cables, a line level amp and a sound processor, I could not eliminate alternator whine in my '05 Mustang GT. I was using a Pioneer X910BT connected to an AudioControl Matrix 6 channel line driver connected to the head unit with 18" patch cables, then with expensive patch cables running to the back of the car connecting to an AudioControl DQXS Six Channel
Digital Crossover/Equalizer driving a JL XD600/6 power amp for the BostonAcoustic SR80 door speakers, 8" door subs (Shelby Kicker) and the Infinity 6 X 9's in the back package tray. The SUB amp was a Coustic AMP600 bridged to drive a JL Audio 13.5 Thin-Line Subwoofer Driver - 13TW5- in a custom sealed box. The sound was great, but the unwanted noise, tho quite low as aggravating, especially given how much I had spent to get right of it. I'm wondering if using speaker level would get rid of that kind of noise.

Denis Vandale
Fri, 07 Oct 2011 19:35:25 +0000

Hey try running your rca cables opposite side of your vehicle than your power cables this includes your remote wire as well and if they do have to cross cross them in a X manner to reduce the pick up of electromagnetism from power cables try to never run them side by side = only + hope this helps

Ahk313
Thu, 07 Apr 2016 13:15:07 +0400

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