question about active low pass filter, (will it work, if the Vin of the Op-amp, also has noise?? )

[MikeMl]

Your description makes my head spin...

Try a simple test. Start with fully-charged batteries. Temporarily disconnect the alternator feed to the auxiliary battery. Turn on all your stuff. Start up the car and race the engine to cruise rpm. Do you hear the whine?

 

[settra]

ok, i will try tommorow for the record, when engine is not running at all, i have no noise...

 

[MikeMl]

ok, i will try tommorow for the record, when engine is not running at all, i have no noise...

No surprise there...

 

[settra]

ok, so.
1) in my current build (DC-AC-DC) , there is noise in the speakers (Without the RCA cground loop isolatorS) , and in the LCD, even without the engine running. i think that this, is true also in the DC-DC build... maybe cause of a ground loop, although i cant see how or where... that noise is "Static" , and it seems to have low freq...

2)when i have the engine running, and cut the feed to the back battery, the noise returns to the "normal" (like when the engine is not running) .

 

[MikeMl]

ok, so.
1) in my current build (DC-AC-DC) , there is noise in the speakers (Without the RCA cground loop isolatorS) , and in the LCD, even without the engine running. i think that this, is true also in the DC-DC build... maybe cause of a ground loop, although i cant see how or where... that noise is "Static" , and it seems to have low freq...

Ok so it sounds like there is a ground loop between the AC switching inverter and the audio devices, but the noise is not a musical whine, more like static?

2)when i have the engine running, and cut the feed to the back battery, the noise returns to the "normal" (like when the engine is not running) .

I dont understand this descripton.

With engine stopped, all you hear is the "static"?
With engine running, and no feed to the rear battery, what do hear?
With engine running and the normal feed to the rear battery, what do you hear?

 

[settra]

Ok so it sounds like there is a ground loop between the AC switching inverter and the audio devices, but the noise is not a musical whine, more like static?

yes. i dont know how to discribe it... i say "Static" becouse, it is diferent than the noise, i hear with the engine, becouse the noise then (that sounds, TOGETHER with the static) is a high piched noise, that rises in Hz, with the engine RPM
apply all those ofc, to the image Huming as well..

I dont understand this descripton.

when i cut the feed to the rear batter, the noise, i hear is the same, as the noise when the engine is not running at all..


but even though, how can there be a ground looop there? its so simple circuit, i cant have made some connection wrong..
is there any change, that ALL (since i tried all) ground points on my trunck are so bad?? i am thinking of bolting a wire, directly to the alternator, and pull it all the way back, for propper ground...

 

[MikeMl]

Is it possible that what you are hearing is only the switching noise of the inverter, which changes pitch when the alternator voltage increases as the engine is reved up. In other words, you are not hearing alternator whine, but you are hearing the inverter, whose switching frequency is effected by system voltage, which increases only when the alternator is charging the batteries?

 

[settra]

nahhh.. as i told you, the same things happen with the DC-DC coverter (no inverter at the systsem), besides, the alternator "Supposedly" gives constant voltage..

 

[MikeMl]

my "inverter" = your "DC-DC converter"

 

[settra]

i dont know... that freq, should be too high to be seen... by the way, i have forgat to mantion all this time., that once, i had my friend come over, and hook the whole car pc, to his battery... (amp and carpc), and there wasent the slightest noise...