I have a 78 with a TPI LTI engine in it. The engine was for a 93 Camaro. I installed the original 8 track radio last week. With ignition on or in accessory the radio sounds fine. When I sart the engine I get a high frequency whine that increases as I increase RPMs. I even get the hum with the radio off! Any suggestions short of putting the original motor back in the car? Roger L. Gibbons


[Modified by Roger L. Gibbons, 7:44 PM 7/6/2002]

 

sounds like a grounding problem to me. make sure that the ground is in solid contact with bare metal.

 

On my '70 there is a condensor mounted on the coil bracket. It is for radio noise suppression. Also the plug wire shielding is for the same purpose. You might check the AIM and see if there is something similar for your year car. ~Juliet

 

Roger, there are two distinct unwanted sound types from most auto sound systems...static from ignition....especially in a vette, that's why the 'shielding' in earlier years....it sounds like the static from an old AM radio...during a storm especially...or when it's out in the country a ways...or maybe old lower frequency short wave receiver....
in a car it will vary with engine speed, but has that distinct static type sound...

NOW, alternator whine is entirely differant, it sounds more like a hearing test type tone, varies with engine speed....alternator whine is worse with cheaper lower powered stereo amps...the one's saying 15 watts/channel or so...
the noise is picked up right off the battery, and if you took an oscilloscope and looked at the 12 feed line, you would see the voltage fluctuate with the passing of the alternator poles by the field, and currents pushed through the diode pack in the current supply mode....-battery charge- if you will....
what is happening is cheaper amps can't adequately filter that type supply signal so it appears across the speakers.....
to help reduce alt whine...you need to take a largish choke which is a coil of wire around a steel transformer type frame, and put it in series with the amp/radio 12 volt feed wire...and then a large electrolytic capacitor to ground, making a filter network.....a fairly decent but not excellant version of these parts used to be sold by radio shack, but you need check for the choke to be still included....I dunno these days....

speaker wires must be run individually back to the amps...of course, NOT through the auto frame for a gound return....
this is a mess that is hard to beat....
easiest thing is buy a higher powered amp, and they usually have a sophisticated power supply in them, that will act as a filter...but the problem can still be picked up by the head end...but maybe your filter can kill it there, usually does....

as you can tell, i'm an old ham/TV/electronics geek for a while now...
any help needed we can go offline...

mrvette72@interstateweb.net


GENE

 

Thanks for the suggestions. MRVETTE, it does seem to be the alternator. The noise is a whine that increases with engine speed. I am sure that GM put as cheap a radio as possible in the car, but I like the 8 track nostalgia and would kike to keep the radio. I will check with Radio Shack for the filter. Are there any construction schematics for building a filter? Roger L. Gibbons