noisy power supply line

[nickthesafe]

Hi Folks, i hope you can help me out with this real irritating problem;

I have a radio scanner installed in my vehicle with an extension speaker plugged into the rear 'extension speaker' socket. It works OK, if a little quiet. So I built a 7w amplifier and hooked it up to the same output of the radio using a loading resistor across the amp input. The amp works wonderfully except that it is picking up bad noise from the vehicles electronic systems. I've tried regulating the supply line, adding extra caps etc, altering the load.... To check the noise wasn't coming down the signal line i coupled the amp to a 12v gel battery and it runs without any noise at all. What do you think guys???.......

 

[Gazza1]

Hi Folks, i hope you can help me out with this real irritating problem;

I have a radio scanner installed in my vehicle with an extension speaker plugged into the rear 'extension speaker' socket. It works OK, if a little quiet. So I built a 7w amplifier and hooked it up to the same output of the radio using a loading resistor across the amp input. The amp works wonderfully except that it is picking up bad noise from the vehicles electronic systems. I've tried regulating the supply line, adding extra caps etc, altering the load.... To check the noise wasn't coming down the signal line i coupled the amp to a 12v gel battery and it runs without any noise at all. What do you think guys???.......

I think this is a better place for you to get an answer

 

[audioguru2]

Your amplifier is amplifying the power supply noise.
But you forgot to attach the schematic of the amplifier for us to see why.

 

[Kevin Weddle]

Why are you loading the input to the amp? I had a cheap car radio, it had a constant buzz to it. I put a little more expensive radio in, it works great. I think your amplifier might be sensitive to a little supply noise, but a better amplifier wouldn't be. As far a fixing the problem, that cheap radio weighed a lot less than the one I have now. You probably can't do anything to turn a cheap amp into better amp.

 

[audioguru2]

Hi Kevin,
The cheap amplifier might be fixed by adding a filter capacitor that costs only 35 cents.
Maybe it has a ground loop that picks up noise.