Question about Kenwood KAC-8403 Car Audio Amplifier

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Beeping sound from amp when car headlights turned on


I have fitted a Kenwood KAC-8403 amp and a KSC-SW1 sub-woofer into my 2006 Subaru Outback 2.5i (with the standard Subaru head-unit). I have absolutely no complaints with either of these components, the sound is fantastic.

However, I do have a problem that I hope you can help me with.

When the amp is powered on (head-unit can be on or off - doesn't matter) and I then turn on the car's headlights, I hear a single (high frequency) beep. This beep then recurs once every 30 seconds to 1 minute, while ever the headlights are on - detracts from enjoying the music somewhat.

When I turn the lights off - no more beeps. I've checked and the sound is coming from my speakers. The amp is connected directly to the car battery (fused) and earthed directly back to it with 4# multicore wire.

Any ideas of the cause and the fix? Hope you can help.


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  • 3 more comments 
  • 7224warren Jan 28, 2008

    No, no power filter and as I said only occurs with headlights (or for that matter, parking lights) switched on.

  • 7224warren Feb 02, 2008

    Thank you for your response, I really appreciate it.

    I don't believe that this is RFI. I have experienced RFI in the past and know what that sounds like (usually alternator whine, which varies in pitch as engine revs vary). Wiring is already shielded and power supply is filtered - using 4# wire for both power and earth - direct to the battery. The amp auto turn-on wire is connected directly to the head-unit power on cable (i.e. auxiliary power on).

    The 'beep' I mentioned is a discrete, clear, generated high frequency sound emanating from my tweeters, not "noise" - it sounds exactly like the beep a digital watch makes if it is set to indicate hours.

    This beep occurs as soon as I switch on the headlight/parking light switch. Even if I switch on only the parking lights, this beep is still generated approximately every 30 seconds to 1 minute - as a clear discrete sound. The rest of the time - crystal clear audio and it still occurs if the amp is turned on but the head unit is switched off (i.e. no audio input).

    I thought that the amp was telling me something, i.e. an audible error code, possibly indicating low voltage. However, Kenwood advises that this amp has no audible error codes ? just accepts the input signal and amplifies it.

    Thinking that it had something to do with voltage drop, I tested this by leaving lights turned off and holding the headlight 'flasher' switch on whilst driving, so that I was running with high-beam on - a fairly good voltage drain - no beeps whatsoever. I've also tested the power to the amp at night with headlights turned on, ignition on and engine off - to put a high load on the battery. Lights exhibit no discernable dimming when amp is on, even with audio at a high volume with a lot of bass and of course beep is still present.

    So, not RFI, and no perceptible voltage drop.

    After some experimenting, I believe I have now found the cause, although I'm baffled as to why or how to cure it. I noticed that when I adjusted the instrument light dimmer switch (standard Subaru switch), I heard a beep. So I did some testing. This rotary switch has 7 positions: 0 - no dimming, through to 6 - instrument lights very dim.

    Results of testing this dimmer switch in each position by switching on parking lights, with the head-unit off, amp on and ignition turned on but ENGINE OFF were:

    · Position 0 (no dimming) - beeps as described above.
    · Position 1 - beeps as described above.
    · Position 2 - beeps as described above.
    · Position 3 - single beep when light switch is turned on and near constant beeps thereafter (i.e. about 1/2 second apart).
    · Position 4 - no beep when light switch is turned on, but beep when switch is turned OFF! And intermittent beeps as above.
    · Position 5 - no beep when light switch is turned on, but beep when switch is turned off and intermittent beeps as above.
    · Position 6 (max dimming) - no beep when light switch is turned on, but beep when it is turned off, BUT no beeps at any other time.

    Very perplexing and I think a quirk of this particular Subaru model (or possibly Subarus in general). The only connection that I am aware of between the dimmer switch and head-unit is that it dims the display lights.

    O.K. I've found the cause, now I can either drive around at night with my instrument lights dimmed to the max, or try to figure out why this dimmer switch appears to be transmitting this weird signal to the amp.

    Any thoughts?

  • 7224warren Feb 02, 2008

    Thanks for your reply Soulvisitor. Please refer to my reply above. Any thoughts?

  • 7224warren Feb 02, 2008

    Thanks for your reply BEERBrooklyn. Please refer to my reply above. Any thoughts?

  • 7224warren Feb 02, 2008

    Yes, if head-unit turned off still hear beeps through tweeters. And as I said not "noise" but rather discrete sound.

    Earth specifics: wire comes from amp to grounded bolt on body subframe cross-bar approx 3 inches from amp. Then wire from this grounded bolt through firewall to grounded bolt on right hand inner rail. Then wire from this grounded bolt to circle earth system mounted on engine and from there back to battery -ve. All 4# wire. I think earthing is taken care of :)

    While I'm at it, +ve comes direct from battery through 75 Amp circuit breaker to amp with nothing else in the circuit. Have tried with and without 1 Farad cap. Subwoofer (Kenwood KSC-SW1) power feeds off +ve terminal on amp.




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It could be a indication of low amps.

Does it happen when car is running and lights are on?

If car is off do lights dim to the music at night?

You could be using more power than your alternator can supply.

Most alternators are capable of producing 55-65 amps. This is adequate for sound systems producing up to 350 watts RMS. Some more modern vehicles have alternators rated up to about 120 amps. This will be sufficient for systems of up to about 600 watts. Some pre-1985 cars, on the other hand, have alternators only rated for 35 amps. This will only support about 125 watts in amplifier power.

One easy, effective solution maybe installing a capacitor. Heavy-duty capacitors connect to the power cable (just before it reaches your amplifier) and act as a buffer zone between your amp and your car's electrical system. They store up a reservoir of power which can supply the amplifier's peak demands (like a bass drum beat) without having to draw current from the battery.

First, Check your earth is excellent and not all clustered on one point. Ensure power leads are thick and secure. Separate speaker and power cables.

Check auto turn on wire (thin blue on amp) is not connected to lights power source, use elect aerial output on head instead

Run 4 gauge earth wire to car body near amp, power cable must be heavy gauge too, expessally with a sub woofer running.
Beeping sound from amp when car headlights turned  - 446801c.jpg

Posted on Jan 31, 2008

  • Soulvisitor
    Soulvisitor Feb 02, 2008

    I'd like to see the earth running to the car body rather than back at battery

  • Soulvisitor
    Soulvisitor Feb 02, 2008

    Also try disconnecting display/lights power if seperate. On second thoughts that shouldn't matter due to sound is present with head off, so scap that, I'd be removing that amps earth and fixing to body near amp, Please confirm if that is correct ie head off still have noise?



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Get your ground from the rear .i thing the ground you are noew using is in the path of you rear lights therefore you will get interference,also you can put a groundloop between radio and amp.that connects to the rca cables.

Posted on Jan 31, 2008

  • 8 more comments 
  • Anonymous Feb 01, 2008

    does your headlights blink when you play music loud?try a not ground your amp. to the battery.get ground from chassis close to amp. be sure to use a wire thats is a larger gauge or equal to the power wire.The lower the gauge the bigger the wire is.the noise you r hearing is from the alternator without a doubt.try a different ground 1st.

  • Anonymous Feb 01, 2008

    1 more question.Is your input cables running along side the power cables to the amp?90% of feedback is cause by running power and speaker cables or input cables parallel .if have to cross do it in na intersecting fashion..good luck. get back to me and rating please.

  • Anonymous Feb 02, 2008

    it could be your head unit.Maybe your power antenna wire from radio is connected to the illumination wire from car.I would check out your head unit connects again.If rADIO HAS ILLUMINATION WIRE I USUYALLLY DOUBLE IT WITH THE SWITCHED WIRE.sorry for yelling.also ii apoligize not getting back sooner .have you tried radio without amp?Your still using stock radio. its probably from your radio.

  • Anonymous Feb 02, 2008

    does your radio have rca jacks?

  • Anonymous Feb 02, 2008

    u have noise with car runnig or off when head unit is not connected to amp?
    do u have a noise filter?or groun loop filter?

  • Anonymous Feb 02, 2008

    how is the amp on if headunit is off?when radio is off amp should also be off.if not u are using a wrong wire 4 remote switch.

  • Anonymous Feb 03, 2008

    that radio beeps when volume is turned up using contol on steering wheel
    how are u connected to amp?

  • Anonymous Feb 03, 2008

    1. more thing u don't want ur ground going back to batterry directly. ,or to the engine ground.just get it from the metal behind seat or somewhere similar.I make my own hole in and put my own screw.usually from some body part of the car for instance trunk quarter panel if in rear .if under seat i go on the door kickers. want to be careful when drilling

  • Anonymous Feb 03, 2008

    1 more thing try disconnect rca from radio to amp. or the input ur using.does it still beep ?if not u can eliminate any groud feedback.also it mean s the problem is in the headunit.

  • Anonymous Feb 08, 2008




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