Free Shipping on Everything.
60-Day Money-Back Guarantee | Lifetime Tech Support

amp powers on but no sound from sub

Car Audio, Video, & GPS

Car Audio, Video, & GPS
Talk about stereos, navigation, amps, subs, and all things car audio

amp powers on but no sound from sub

This question is answered

so i just got an amp (rockford p4004) to replace my old one.  i thought i wired it correctly. the amp will power on, but im not getting anything from my sub.  the only thing i can think of is the input is wrong.  i tried the rear input, and the pass over input.  tried the sub bridged and regular. anyone have any ideas?  can i try the inputs flipped or is that bad for the amp? i might have connected them backwards in the first place as they are black and grey not red and white

Verified Answer
  • You only have 1 pair of RCA outputs coming from your head. Set it on 'sub' in your head. Connect those to the rear RCA input of the amp. Use a 2 channel LOC http://www.crutchfield.com/p_142LOC80/Scosche-LOC80.html and connect the front speaker wire outputs from the head to the front RCA inputs on the amp. Set the rear channels of the amp to LPF and the front channels of the amp to full. You have lowpass settings in your head, set it on 85 hz.  Set the amp to 4 ch operation. Set the rear freq to 100. Set both punch EQ knobs to min. Connect your front speakers to the speaker outputs normally. Connect the sub to the rear bridged speaker outputs. Do you know the correct way to set the gains ? In the head, set the subwoofer level to 8. Amp gain control to high. Loudness off.

    GLH Geeked

All Replies
  • What do you mean by "rear input" or "pass over input"?

    Are you using high level (speaker wire) inputs, or line level (RCA cable) inputs?

    Are you still using the factory head unit or an aftermarket head unit?

  • lol thats what im trying to figure out too. theres only three inputs i see.  they are all the red/white rca inputs.  one says front input, one says pass thru, and the other says rear input. im connecting from a jvc head unit. just not sure where to connect it to. its a jf p4004 if that helps

  • figured it out. just had to use the front inputs lol.  quick question though. i just read that the fuse for the power wire is supposed to be up by the battery, and mine is by the amp.  should i flip the wire, or is it a big deal?

  • Yes, it's a big deal. The inline fuse should be within 18 inches of the battery.

    Usually, when using a 4 channel amp with a subwoofer, the sub RCA output from the head is connected to the rear RCA input on the amp, then the rear speaker output on the amp is bridged to the subwoofer. The sub present a 4 ohm load to the amp.  Pass through is for daisy chaining another amp.

    What is the model number of the JVC head and the make and model number of the subwoofer ?

    GLH Geeked

  • The head unit is a jvc kd-r330 and the sub is a kenwood kfc w3003.  if im trying to wire the sub and front speakers to the same amp, will i need two diff inputs?

  • You only have 1 pair of RCA outputs coming from your head. Set it on 'sub' in your head. Connect those to the rear RCA input of the amp. Use a 2 channel LOC http://www.crutchfield.com/p_142LOC80/Scosche-LOC80.html and connect the front speaker wire outputs from the head to the front RCA inputs on the amp. Set the rear channels of the amp to LPF and the front channels of the amp to full. You have lowpass settings in your head, set it on 85 hz.  Set the amp to 4 ch operation. Set the rear freq to 100. Set both punch EQ knobs to min. Connect your front speakers to the speaker outputs normally. Connect the sub to the rear bridged speaker outputs. Do you know the correct way to set the gains ? In the head, set the subwoofer level to 8. Amp gain control to high. Loudness off.

    GLH Geeked

  • ok so for the front speakers i run the speaker outputs on the head through the converter to the amp, andn from the front outputs of the amp to the speakers? what youre saying makes perfect sense, but i tried running the rca from the had to the rear input on the amp, and then had sub bridged on the rear channels, and it didnt work. this was without the speakers at all. any ideas? 

  • You're scaring me a bit here ...

    As GLH said, the best way to wire this is with the LOC to the front inputs on the amp, HU RCA's in sub mode to the rear inputs and rear inputs bridged to the sub.  The PASS-Thru inputs will not be used.

    If you don't care about the fader control and especially if you have the remote bass control for the amp, an easier connection is:  Set the HU RCA's to "Rear Mode" - Run the RCA's to the FRONT inputs on the amp, and set the amp to 2-CH mode.

    Hope This Helps!!!

    Anyone else have suggestions?

    2002 Ford Focus JVC KD-A815 Sony CDX-GT410u Sony XT-100HD HD Tuner Stock speakers, no amp, no subs

  • ok so i got it figured out lol. the problem was when i hooked up the amp it reset the head and switched it back to rear instead of sub and it didnt realize it. one last question. does the 2/4 channel switch have to do with the input or output of the amp? thanks for bearing with me guys im learning as i go.  glh and tigerheli you both have been amazingly helpful

  • srkasdorf
    does the 2/4 channel switch have to do with the input or output of the amp

    Both I reckon we could say. When switched to 2 ch, only the front inputs are enabled, which are split into 4 outputs. So, if your head has front and rear/sub RCA jacks, and you need to use the rear/sub for a sub amp, you can connect the front output from the head to the front input on the amp, and still have 50 watts RMS to 4 speakers, but no fader.

    GLH Geeked

  • I think GLH misunderstood the question (maybe not ...).

    The amp has a 2/4-channel switch.  In 4-channel mode, the Front RCA inputs receive one signal (preferably from the HU Front RCA's), and the Rear RCA inputs receive a different signal (preferably from the HU Rear or Subwoofer RCA's).  In 2-channel mode, whatever signal is sent to the Front RCA's is passed to both the front and rear output channels and no input is required on the amp Rear RCA's.

    Now, if your HU had Front and Subwoofer RCA's, you would set the amp in 4-channel switch mode, run the HU Front RCA's to the Front inputs on the amp and the HU subwoofer RCA's to the Rear inputs.  (This is what GLH was recommending with the LOC).

    If the switch is in 2-channel mode, the front RCA inputs are sent to all channels of the amp - this COULD work for you as well.  In this case, you want the HU RCA's in REAR mode (b/c in subwoofer mode, the LPF would block any sound from getting through).  Run the HU RCA's to the front inputs of the amp and run the front outputs to your front speakers and the rear outputs to your sub.  You would want the fader fully rear as you are only using those RCA's and are driving the front speakers with them, but you could hook up rear speakers to the HU outputs and use the amp front gain controls to blend the sound.  (This example gets confusing b/c you are using the HU REAR RCA's to drive your front speakers, but it works if you don't care about the fader control).

    Hope This Helps!!!

    Anyone else have suggestions?

    2002 Ford Focus JVC KD-A815 Sony CDX-GT410u Sony XT-100HD HD Tuner Stock speakers, no amp, no subs

  • hey thanks alot guys.  i know im asking a million questions here, but can you tell me if my head can power the rear deck speakers i have well enough? the head is actually a kd-r320, and the speakers are ts a6994r. also i read something on crutchfield about gain tuning that said you shouldnt use a head lpf and amp lpf at the same time. so shouldnt i set the head to rear and just use the amps lpf? or vice versa?

  • TigerHeli
    maybe not

    Correct.

    TigerHeli

    The amp has a 2/4-channel switch.  In 4-channel mode, the Front RCA inputs receive one signal (preferably from the HU Front RCA's), and the Rear RCA inputs receive a different signal (preferably from the HU Rear or Subwoofer RCA's).  In 2-channel mode, whatever signal is sent to the Front RCA's is passed to both the front and rear output channels and no input is required on the amp Rear RCA's.

    Exactly what I meant.

     

    GLH Geeked

  • srkasdorf
    can you tell me if my head can power the rear deck speakers i have well enough?

    Define well enough.  It's a 20W head unit powering 80W RMS speakers.  It's probably doing so now, correct?  It's not going to compete very well with 50W RMS to your front speakers, but generally that's not what you are looking at with rear speakers anyway.

    srkasdorf
    also i read something on crutchfield about gain tuning that said you shouldnt use a head lpf and amp lpf at the same time.

    That's been contradicted a few times - it introduces a phase shift and causes a sharper roll-off slope, but otherwise it isn't really a big deal.

    srkasdorf
    so shouldnt i set the head to rear and just use the amps lpf? or vice versa?

    Okay - if you are using a LOC to keep fader control, you want the HU RCA's in SUB mode, and you could either set the LPF from the HU, the amp, or both.

    If you are NOT using a LOC and are using the HU RCA's to the amp FRONT inputs and the 2-channel mode to feed the sub, you want the HU RCA's in REAR so that your front speakers get a full-range signal and then you want to set the LPF (and HPF) on the amp only.

    Hope This Helps!!!

    Anyone else have suggestions?

     

    2002 Ford Focus JVC KD-A815 Sony CDX-GT410u Sony XT-100HD HD Tuner Stock speakers, no amp, no subs

  • how much rms power can i get from the head with the built in amp? ie loud mode