amplifier works connected to PC .. but not when connected to car radio - diyAudio
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Old 1st March 2011, 01:38 AM   #1
Join Date: Aug 2007
Default amplifier works connected to PC .. but not when connected to car radio

i have a klipsch promedia 2.1 system.
today i tried to hookup the subwoofer and amplifier in my car.

i have a 400 watt power invertor.
the back of the amp says it only needs 240 watts.
the amplifier turned on and the lights lit up just fine.

but when i connected the preamp outputs of the radio to the amplifier, the sound was extremely weak.
so weak, infact, that i couldnt hear it playing in the trunk until i went to the rear of the vehicle.

at first i thought maybe my preamp outputs werent working.
so i plugged in some headphones and heard output.. which told me that the preamp was working.

the radio documentation says that the preamp voltages are 5 volts.
the soundcard documentation says the preamp voltages are 2 volts.

the subwoofer was working fine in the house connected to the computer.
but, again, when i hooked it up to the car radio.. there was very little output.

i brought the subwoofer back into the house and connected it to the computer again, and it worked just fine.

what is going on here?
is the input resistance of the subwoofer too high?
what does that say about the soundcard output??
and how is the subwoofer supposed to work with an ipod or anything else that plugs into the auxiliary port.

i didnt use the auxiliary port.. i used the same 3.5mm stereo jack that plugs into the computer soundcard.

i want to know why it didnt work for me and if there is anything i can do to make it work.

i suppose i could try to run an extension cord from the house and plug it in.. then try again.
i find it hard to believe that a 400 watt power invertor isnt powering the subwoofer amplifier that requires 240 watts.
i mean.. if i turned the amplifier gain up more than half-way, there was ground noise (maybe cheap rca cables?)

i have used the car radio with regular car amplifiers before and those amps worked.
why is the subwoofer not working in the car?
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Old 2nd March 2011, 07:42 PM   #2
Join Date: Aug 2007
okay.. i got it to work.

i didnt have to ground the preamp wires last time i had a car amp hooked up.
but i grounded the preamps to try and make my subwoofer amp's ground noise disappear.
then i left 'em grounded for the main amp and forgot.

(there was no need to ground the preamp wires with the single main amp.. because it wasnt grounded until i tried to hookup the subwoofer amp)

when i disconnected the amp.. i removed the ground wire and added it to the main ground.

after putting the ground wire back on the preamp outputs, the subwoofer began to play.
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