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Car radio hum

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April 17, 2005 9:38:43 PM

Archived from groups: rec.audio.tech (More info?)

Before getting rid of an old car, I salvaged the radio, which is excellent,
for use in my basement. I had an old 12V adapter and a couple of speakers
which I hooked up and it works very well. The only problem is a bit of hum.
I'm sure the radio is OK because there was no hum in the car. Could the hum
be caused by a faulty adapter which needs more filtering? If so, is there a
simple way of doing this?

More about : car radio hum

Anonymous
April 17, 2005 9:38:44 PM

Archived from groups: rec.audio.tech (More info?)

The 12V adapter doesn't have enough filtering. Look for a regulated
supply to avoid hum problems. It is unlikely that you would be able to
modify the adapter cost effectively. You could try adding more
capacitance and a voltage regulator but packaging would be an issue and
the adaptor may not have a sufficiently high output voltage for the
regulator to function.



Norman wrote:
> Before getting rid of an old car, I salvaged the radio, which is
excellent,
> for use in my basement. I had an old 12V adapter and a couple of
speakers
> which I hooked up and it works very well. The only problem is a bit
of hum.
> I'm sure the radio is OK because there was no hum in the car. Could
the hum
> be caused by a faulty adapter which needs more filtering? If so, is
there a
> simple way of doing this?
Anonymous
April 18, 2005 1:07:30 PM

Archived from groups: rec.audio.tech (More info?)

For your car radio, you will need a regulated power supply that is properly
filtered, and rated for the current load of the radio.

--

JANA
_____


"Norman" <normanwt@optonline.net> wrote in message
news:BE884FA3.307B9%normanwt@optonline.net...
Before getting rid of an old car, I salvaged the radio, which is excellent,
for use in my basement. I had an old 12V adapter and a couple of speakers
which I hooked up and it works very well. The only problem is a bit of hum.
I'm sure the radio is OK because there was no hum in the car. Could the hum
be caused by a faulty adapter which needs more filtering? If so, is there a
simple way of doing this?
Related resources
Anonymous
April 18, 2005 1:07:31 PM

Archived from groups: rec.audio.tech (More info?)

"Norman" wrote ...
> Before getting rid of an old car, I salvaged the radio, which is
> excellent,
> for use in my basement. I had an old 12V adapter and a couple of
> speakers
> which I hooked up and it works very well. The only problem is a bit of
> hum.
> I'm sure the radio is OK because there was no hum in the car. Could
> the hum
> be caused by a faulty adapter which needs more filtering? If so, is
> there a
> simple way of doing this?

The simple way is to add filter capacitor(s). However,
note that a "12V adapter" of the kind used for charging
batteries, etc will possibly have a too-high voltage when
you hang suficient filtering capacitance across it. Might
even be worth getting a smalish 12v lead-acid (or "gel-
cel") battery to serve dual purpose of filter "capacitor"
and "battery backup".
Anonymous
April 18, 2005 5:52:44 PM

Archived from groups: rec.audio.tech (More info?)

On Mon, 18 Apr 2005 07:34:47 -0700, Richard Crowley <rcrowley7@xprt.net> wrote:
>"Norman" wrote ...
>> Before getting rid of an old car, I salvaged the radio, which is
>> excellent,
>> for use in my basement. I had an old 12V adapter and a couple of
>> speakers
>> which I hooked up and it works very well. The only problem is a bit of
>> hum.
>> I'm sure the radio is OK because there was no hum in the car. Could
>> the hum
>> be caused by a faulty adapter which needs more filtering? If so, is
>> there a
>> simple way of doing this?

>The simple way is to add filter capacitor(s). However,
>note that a "12V adapter" of the kind used for charging
>batteries, etc will possibly have a too-high voltage when
>you hang suficient filtering capacitance across it. Might
uh... I don't think so.

Filtering will give you the average of the signal presented.

If you try using a "battery charger", you're going to instantly fry your
equipment. 50V spikes wouldn't be unusual. Putting filtering on it will
probably blow up the filter caps. It won't raise the average voltage.

The OP obviously didn't fry his radio, so I think it's a safe bet that he
was simply using a 12V supply albeit a badly filtered one. Putting some
decent filtering on it won't raise the voltage.


>even be worth getting a smalish 12v lead-acid (or "gel-
>cel") battery to serve dual purpose of filter "capacitor"
>and "battery backup".
April 19, 2005 5:45:07 AM

Archived from groups: rec.audio.tech (More info?)

>Before getting rid of an old car, I salvaged the radio, which is excellent,
>for use in my basement. I had an old 12V adapter and a couple of speakers
>which I hooked up and it works very well. The only problem is a bit of hum.
>I'm sure the radio is OK because there was no hum in the car. Could the hum
>be caused by a faulty adapter which needs more filtering? If so, is there a
>simple way of doing this?
>
>
>
Just a layman's 0.02... but what about earthing? I know from very limited
experience that improper earth connections cause the kind of hum you describe.
Also, some (perhaps most?) car radios are earthed through the antenna connector,
to the car's chassis.

Anyway, I messed around with a similar set-up, and only got good results when I
connected the negative lead to the antenna socket. OK, so that contradicts what
I've said above... anyway, I was using a standard selectable voltage adapter,
which I doubt is very well regulated, and managed to get a clean sound in the
end (from the cassette deck, I didn't try using the radio function). But that
was simply because a lack of regulation/filtering never occured to me as a cause
of the problems.

Hope this helps, at least a little,

Adam.
Anonymous
April 19, 2005 6:48:10 AM

Archived from groups: rec.audio.tech (More info?)

"Norman" <normanwt@optonline.net> wrote in message
news:BE884FA3.307B9%normanwt@optonline.net...
> Before getting rid of an old car, I salvaged the radio, which is
> excellent,
> for use in my basement. I had an old 12V adapter and a couple of speakers
> which I hooked up and it works very well. The only problem is a bit of
> hum.
> I'm sure the radio is OK because there was no hum in the car. Could the
> hum
> be caused by a faulty adapter which needs more filtering? If so, is there
> a
> simple way of doing this?

I used to bench test car radios using a 12-volt car battery charger and a
5000uf/35v capacitor that I put inside the charger case (there was plenty of
room). Worked just fine. Car radios aren't that finicky about regulation,
but they don't expect 120 Hz ripple.
Anonymous
April 21, 2005 12:47:20 AM

Archived from groups: rec.audio.tech (More info?)

Norman wrote:

> Before getting rid of an old car, I salvaged the radio, which is excellent,
> for use in my basement. I had an old 12V adapter and a couple of speakers
> which I hooked up and it works very well. The only problem is a bit of hum.
> I'm sure the radio is OK because there was no hum in the car. Could the hum
> be caused by a faulty adapter which needs more filtering? If so, is there a
> simple way of doing this?
>
You should have "salvaged" the car battery too. Then you could have just
run it off the car battery and recharged it with you not so clean power
supply when it ran down.

Bob

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