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  1. #1

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    Default Decent amplifier to run polk audio db691's and db571's.

    I just recently installed a kenwood KDC-BT945U HU (50W peak x 4), polk audio db571's (75w rms) in the doors, db691's (100w rms) in the rear deck of my mercury grand marquis.

    My old car (also a MGM) has some wal-mart special pioneer speakers in similar dimensions but an older less featured kenwood HU, KDC-X692.

    It seems the polks need more power than the pioneers as I can not sustain 70% volume out of the head unit before the volume output drops dramatically. If I turn the HU down for about 30 seconds, then turn it back up, it's fine for a few minutes and drops output volume again. This happens around volume #24 (out of a 1-35 range).

    At volume 23 the speakers sound fantastic and pound pretty hard for not running a sub.

    If this theory doesn't sound right, please let me know why.

    With that in mind, I think in order to not burn up my HU, I need to get a 4-channel amp to run the speakers. It's been 15+ years since I bought an amp for a car (college), but I always favored kenwood head units in cars and polk speakers in my house, so I figured both in my car would suit me well.

    Just thought I'd ask what's out there these days that is relatively economical/reliable that will run these speakers.

    Any info would be appreciated.

  2. #2

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    Yeah that doesnt sound right at all. If your volume is dropping off at a certain volume setting, thats a hardware issue or possible a charging issue. If its a charging issue youve got a dead battery or close to it cause a head unit doesnt take that big a draw.

    So an amp might not fix this is the head unit itself is faulty. Youll be using the passive RCA's out of the head unit to the amp but youll still be using the head unit's volume control. Theoretically it shouldnt continue because the RCA's arent putting out any wattage and shouldnt draw any excess current. But if its a charging system issue then there is no way itll support an amp cause an amp will draw twice or more times the juice than a head unit will.

  3. #3

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    I had something similar before with a JVC arsenal head unit. It's why I ended up with the kenwood I have in my other car. With factory speakers, I could crank it up, but the speakers sounded horrible. Upgraded the speakers and I couldn't turn it up nearly as high as I could with factory speakers or the speakers would make a horrid popping sound and the volume would trail off.

    This is kind of why I think I'm overdriving the head unit amp.

  4. #4

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    Oh ok, yeah that popping sound is the head unit clipping. So yeah you need an amp cause that head unit ain't getting the job done.

  5. #5

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    You might consider looking at the Kenwood XR series amps. I have the 5-channel version (XR-5S), and am very happy with it. It sounds fantastic, and is built very well. When I first picked it up, I was very surprised at just how heavy that little amp was. Also, due to its small size, it is easy to hide even in a space limited car.

    I know they make a 4-channel version as well, the XR-4S.

  6. #6

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    I ended up buying an older 4 channel kenwood, KAC-8452. 800W peak, 70W RMS x 4 @12V. Just tested it out on my bench and seems to work fine. $80 shipped via ebay. Getting it installed tomorrow using 4 gauge wire and a spare set of rca's for a sub if I decide to get one down the line. Figured I might as well wire for it just in case so I don't have to pay twice.

    Is pretty big, but it's going in a grand marquis in the trunk... so I have room. :)

  7. #7

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    Well, still have a volume issue.

    I have disconnected the ground/power cables the installer put on the amp, removed the ends (one fell of in my hand), soldered new ends on and regrounded the ground cable to my car body in a thicker area with a 1/2" bolt/nut vs self tap screw that they used. AWG4 for power/ground, 16G for speaker, twisted pair kicker RCA's for the low level lines.

    Have bypassed the HU with a MP3 player directly to my amp and after about 15 minutes of heavy use, the volume drops.

    Volume still falls off after about 15 minutes of hard use.

    The HU puts out more power to the RCA's than the portable mp3 and since I ruled out the HU as the issue, I plugged it back in. There's a fine line between where the volume drops and where it doesn't drop. If I leave the volume on that line, the volume fluctuates repeatedly on it's own. Currently, around 28 on the HU dial (1-35 range). If I bump up the volume to 33-34, it's just as loud as it was at 28 before the volume dropped and it seems to hold there without degradation of sound quality or fluctuation of volume.

    What I did notice was that the magnet area on the 6x9's in the trunk do feel warm to the touch (55F ambient, probably 80F to the touch). The amp is fairly hot to the touch in one area, would assume around 140F but will use my IR therm to confirm.

    I'm going to recheck where I made the ground connection to make sure I sanded the area clear of paint and see if I can figure out if I have a high ohm ground to the battery terminal. Just need to find a decent hunk of wire that can go that far with my meter.

    These speakers sound phenomenal... right up to the point the volume drops out. When it drops out, it's the entire frequency range. With the amp, it doesn't crackle or sound bad at all, it just sounds like I turned them down. When I turn the volume up further, they pound just as hard and sound just as good as they did.

    Would just like to resolve this issue as it's a stupid issue to have and whatever it is, I'm afraid of it causing overheating somewhere.

  8. #8

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    If you are aiming for a good A/B amp you could consider Mtx amps. Something like the new Road Thunder line would be good. http://www.crutchfield.com/p_236RT60...ORID236&tp=115

    Also, as a very cheap solution, has anyone heard any system with Sound Ordnance Amps (Crutchfield amp line)? They come with 3 year warranties. http://www.crutchfield.com/p_236RT60...ORID236&tp=115

    If you are ok with class D, you could try the new Polk line, Alpine MRX series, or JL XD series. Alpine and Jl are going to be in $300 to $400 series.

    Something to consider about how much to pay for an amp. Upgrading speakers, adding equalization, time alignment, going active, will make a much more significant improvement on SQ then will going with an expensive amp. You have entry level speakers, which are a good bang for your buck so try for the same in your amp. Your standard right now is deck power, any good entry amp is going to sound much better than what you have now. Just get something reliable that won't melt on a hot summer day.
    Last edited by pentoncm; 09-24-2011 at 05:52 PM.
    Audison Bit Ten
    Kenwood X595
    Polk MM6501
    Polk MM1240
    Mtx 704x
    Alpine MRX50

  9. #9

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    Guessing you meant one of these for the sound ordnance amp:
    http://www.crutchfield.com/p_777M407...d+ordnance+amp

    I was off on how hot the surface of the amp got, it was at 115F and the 6x9 was 90F. Ambient, 50F.

    Took it out and drove it around again tonight after cleaning the paint off the surface of the car for the ground connection I had made and making sure the spade connectors on the rear speakers were tight. Also roughed up the surface of the terminator for the ground with sandpaper.

    My car has 2 AWG 6 wires coming off the battery. One to the frame and one to the engine block. The hot wire is larger, would guess at least AWG 4.

    Since it was night, I had the headlights/foglights on and noticed no dimming whatsoever when I had it hitting hard. Volume still drops out after 15 minutes of run time.
    Last edited by olds97_lss; 09-24-2011 at 09:23 PM.

  10. #10

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    If your amp is 115F externally, it's probably hotter inside. It really sounds like it's going into a thermal protect mode by the way you describe it. Here's a test that may help confirm it. Get a house fan and aim it directly over the hotspot on the amp then run it like you normally do. See if it still drops the volume at the 15 minute mark. If it takes longer or doesn't drop at all, you've just confirmed that it is an overheating issue.

  11. #11

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    Would be nice if there was a way to test the amp or speakers without buying something new and hoping... Anyone have any suggestions?

    Anyone think the speakers are generating a higher ohm rating as they warm up? Not sure my multi-meter will be able to show me the diff between 4 ohms and 4.27 ohms... but is something I may look at.

    Does higher ohms cause less output or is it lower ohms? Wondering if maybe I should look for some 2-ohm speakers...

  12. #12

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    Set the volume on the hu to about 80% in your case about 28. Do you have the volume drop issue here? If you do, turn the gains down a bit and try again. Set the gains at the point where at 28 volume you don't driver the amp into protect mode.

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