hiss from fm modulator
Thread Starter
Instructor
Joined: Mar 1999
Posts: 189
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From: San Diego CA
hiss from fm modulator
I have put a fm modulator into the cavity behind the ac controls in a 02 z06. There is no hiss coming through the system when i just turn the key to the accessory position, but as soon as I crank the engine the hiss noise quadruples. The modulator is connected to the switched accessory power in the passenger footwell. What can I do to get rid of this noise? thanks for the help.
Melting Slicks
Joined: Sep 2000
Posts: 2,756
Likes: 5
From: Satellite Beach, FL, USA
Re: hiss from fm modulator (tolgademir)
It really depends on the quality of the FM mod and if noise on it's power lead, indirectly modulates the modulator.
You also need to see if you have caused a ground loop in the audio inputs to the modulator.
You need to make sure that the audio inputs to the modulator and their return, are not carrying power currents. The power currents could be coming down the antenna shield.
You might try to isolate the problem by disconnecting the FM output from the modulator and couple it to a hand held FM radio. If the noise goes away, then power currents are traveling down the coax and casuing a ground loop in the audio inputs.
You also need to see if you have caused a ground loop in the audio inputs to the modulator.
You need to make sure that the audio inputs to the modulator and their return, are not carrying power currents. The power currents could be coming down the antenna shield.
You might try to isolate the problem by disconnecting the FM output from the modulator and couple it to a hand held FM radio. If the noise goes away, then power currents are traveling down the coax and casuing a ground loop in the audio inputs.
Thread Starter
Instructor
Joined: Mar 1999
Posts: 189
Likes: 0
From: San Diego CA
Re: hiss from fm modulator (99HT)
99HT, thanks for your help. I don't think the problem is the second scenario, as there is negligible noise, when the key is in the ACC mode. At this point I am confused on what to do, as there is almost no noise when the key is in the ACC mode (while the engine is not running), and the noise goes very high as soon as the engine starts running. Is there a way to filter the noise the engine is generating. Will a direct line to the battery or connecting the modulator to the always on power help this situation?
Melting Slicks
Joined: Sep 2000
Posts: 2,756
Likes: 5
From: Satellite Beach, FL, USA
Re: hiss from fm modulator (tolgademir)
It is more likely that you have caused a ground loop in the audio input instead of noise riding the power lead into the modulator. A car generates a lot more noise when it is running. This noise can ride on any ground return wire or antenna coax shield, summing with the audio input. Try disconnecting the modulator antenna lead and couple it to a portable FM receiver.
