12 volt car power

[intlplby]

how good a source is 12v car power coming through a the cigarette lighter sockets


it comes off a battery but there is also the alternator in the system .... since it is a battery is it a pretty noise free source or not"?

also, is it possible to make a DIY amp for a 12volt car source that can drive AKG 1000s well? if so what DIY amp would work?

 

[Nisbeth]

The battery itself is a near-ideal power source. But as you say, depending on how the alternator and other electrics are wired, the power might be very noisy because. If you have the option, you can probably use an o-scope to see how much AC is on the power lines. Otherwise, if you have an amp that can be modified for DC-power you could just try it and see how much noise you're able to hear.


/U.

 

[rickcr42]

Quote:

how good a source is 12v car power coming through a the cigarette lighter sockets

Can be absolutely brutal unless filtered with an LC filter inline with the equipment .

The audio system that comes with the automobile already has this "hash' filter built in .
The noise is is Rf from the rectifiers in the alternator that charges the battery . The battery itself is clean but the charging and ignition system are a noise factory.

easy fix would be to insert a 100uH/3A inductor inline with the DC power lead to your portable (if that is what you are talking about using) . Radio Shack did carry the part for a couple of bucks but if they still do or not i don't know

 

[tangent]

The one time I tried this, simply soldering a 78L10 or 78L09 inline with the input power gave quiet enough power for a MINT. Remember, you've got car noise to mask low-level hum and hash, so you don't need to get super regulation.

 

[rickcr42]

one thing about using a regulator straght from the lighter plug is : without some kind of input protection you could wipe out the regulator on start up unless it is unplugged.If you connect a voltmeter across the plug and then turn the key you will see the "spike' and this is at high amperage.

The ideal solution would be -

Lighter Plug/CLC snubber/REG/CLC or CRC filter

clean sound and full regulation

 

[tangent]

Quote:

you will see the "spike'

How high? This type of regulator is rated for 30V. A spike is short in duration by definition, so up to 30V nothing should happen. Now, if it's, say, 40V, then yes, I'd expect it to die immediately.

Quote:

this is at high amperage.

You mean high amperage is available. If a voltage spike shorts something in the regulator, yes, high amps will go through that short and you'll let the magic smoke out of the regulator. Amperage has nothing to do with the failure itself, just how spectacular the aftermath is.

I point this out because it comes back to voltage again. So, how high?

 

[rickcr42]

Quote:

How high? This type of regulator is rated for 30V. A spike is short in duration by definition, so up to 30V nothing should happen. Now, if it's, say, 40V, then yes, I'd expect it to die immediately.

Quote:

You mean high amperage is available. If a voltage spike shorts something in the regulator, yes, high amps will go through that short and you'll let the magic smoke out of the regulator. Amperage has nothing to do with the failure itself, just how spectacular the aftermath is.

voltage has nothing to do with it. just because a part has a high input rating does not mean it can handle a sudden transient at rf frequencies which can and does burn out semiconductors all the time .
that is where tubes have always had an advantage-delicate tubes are not and they take a hell of a beating on "spikes"

Why else you think tactical bombers use tube electronics ?

an EMP that would wipe out any known solid state equipment will barelly cause a burp from the tubes .

As stated-alternators out high frequency hash- noise-garbage and must be filtered at some point and and igition spike can cause equipment failure unless steps are taken.

why do you think car radios turn on slowly and not immediately when the car is powered ?

It isn't about radio/amp warm up time for best sound but a protection mode to prevent failure of the electronics


leave a portable device plugged in on start and you may get away with it or you may not but I don't take the chance -I unplug before exiting the car and don't plug back in until after it is started plus i filter my DC outlet panel with with inline inductors rated at 100uH @ 3A follwed by a shunt capacitor.

any regulators have the in this case required reverse polatiry diodes and current limiting

 

[intlplby]

i guess i shouldnt even be worrying about noise... my concern was the safety of the amp....

my car is a 1966 fj40 landcruiser with only a bikini top..... i hear everything....

i have an aftermarket MSD electronic ignition system and an aftermarket wiring harness.....i cant remember if the harness had any sort of regulating devices when i put it in

basically i should never have my amp plugged in when starting or stopping the car

 

[rickcr42]

Quote:

basically i should never have my amp plugged in when starting or stopping the car

I will tell you what finsally convinced me .about 20 years ago all og my 'mobile music" was in the form of cassettes.I would be driving and listening to music and when i pulled in the driveway just turn off the car while the music was playing and get out.
No big deal.
but from time to time when i would get in and start the car up the cassette would start to play but at something like 20X speed !
Again no big deal.Noted , filed and forgotten.

But every once in a while the tape would spin up ,do the "chipmunk voice" thing and then self destruct !
The tape could not slow down so it spilled from one side faster than the other side could take up the slack and the reult was tape wrapped around the capstan.
And THIS meant taking the damn thing out ,opening it up and removing the tape that was wrapped around everything.The casstte would be ruined but that mattered little-I recorded my own from LPs .

This would happen every so often and it never dawned on me to think about what was going on here until one day a particularly favorite tape was eaten by the "tape monster" and i was on the road so making a copy was out .i thouyght about "why is this happening" and I realised the motor was spinning up faster than normal only on start up so SOMETHING must be going on that is different.
It was different .
The "instant on" from a cold start was throwing a very non linear voltage at the casstte deck and I reasoned further that this "non linear voltage" must be WAY out of the norm or the motors of the deck would barely be noticing it.
After all , automobile audio gear is specifically designed for an environment of temperature extremes and an "unpredictable" power source that would range in voltage from below 12 volts to a high of near 14 volts (alternator guage boys and girls ) so something drastic was happening at the "startup" !

And that something was mentioned above : a wildly unpredictable and non linear voltage spike filled with all kinds of garbage.

So yeah.Unplug the amp when starting up the car or add some inline protection.It took me forever to finally "get it" but once i did the habit stuck and is still there even though my vehicle has not even SEEN a cassette tape.

I wonder how many blow gear in the car from the above mentioned scenario and then blame it on something else because they are not putting 2+2 together and coming up with 4.