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Audiovox Wired FM Modulator Whines



 
 
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  #1  
Old July 12th 06, 03:52 PM posted to rec.audio.car
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Posts: 2
Default Audiovox Wired FM Modulator Whines

Just installed my second Audiovox FMM100A wired FM modulator. The first
one had a high-frequency "whine" (like a carrier tone, but audible)
even with no audio source feeding the box and with the car engine shut
off. It's like taking a hearing test at the doctor's office with very
high-pitched tones. Audiovox tech support said that shouldn't happen
(the most dangerous words in technology: "it *should* work" followed
closely by "that shouldn't happen") and advised me to return it. The
second unit performs identically. It's not that I'm overly sensitive to
high freqs; the rest of my family hears it, too.

I've tried relocating the ground, feeding power from a separate
battery, wrapping the loose wires separately, enclosing the whole
package in foil and connecting that to ground with a capacitor to
intercept stray RF, etc.

The whine isn't as audible while driving, but it's loud enough to be
annoying even with the car radio treble turned down a bit. Otherwise it
works like a charm: when switched on, it routes the audio through the
car speakers on one of two FM frequencies even if there's a strong
station on that freq.

Anyone else have this problem? And/or a fix?

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  #2  
Old July 13th 06, 01:26 PM posted to rec.audio.car
e-nigma
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Posts: 180
Default Audiovox Wired FM Modulator Whines


> wrote in message
oups.com...
> Just installed my second Audiovox FMM100A wired FM modulator. The first
> one had a high-frequency "whine" (like a carrier tone, but audible)
> even with no audio source feeding the box and with the car engine shut
> off. It's like taking a hearing test at the doctor's office with very
> high-pitched tones. Audiovox tech support said that shouldn't happen
> (the most dangerous words in technology: "it *should* work" followed
> closely by "that shouldn't happen") and advised me to return it. The
> second unit performs identically. It's not that I'm overly sensitive to
> high freqs; the rest of my family hears it, too.
>
> I've tried relocating the ground, feeding power from a separate
> battery, wrapping the loose wires separately, enclosing the whole
> package in foil and connecting that to ground with a capacitor to
> intercept stray RF, etc.
>
> The whine isn't as audible while driving, but it's loud enough to be
> annoying even with the car radio treble turned down a bit. Otherwise it
> works like a charm: when switched on, it routes the audio through the
> car speakers on one of two FM frequencies even if there's a strong
> station on that freq.
>
> Anyone else have this problem? And/or a fix?
>


I have seen this happen before with that unit.
If you unplug the RCA inputs to the modulator, is the sound still there or
does it go away?
If it goes away then the problem may be the source unit. It could also be
radiated in from the RCA cables.
The RCA cables may be running near Vehicles computer or other electrical
devise.
If you still have the whine when you unplug the RCA's then It would have to
be the modulator or the power source.


  #3  
Old July 14th 06, 07:09 PM posted to rec.audio.car
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Posts: 2
Default Problem Solved (Was: Audiovox Wired FM Modulator Whines)

The high-freq. noise was there whether anything was plugged into the
RCA connectors or not. It was slightly louder with a DVD player
connected and with the engine running, but it was evident even when
just plugged into the radio antenna, even running on its own 12v power
supply (i.e., not the car battery).

The modulator comes with an isolation transformer which Audiovox tech
support advised me should be installed. It was, but had zero effect.
The spurious noise was not coming in through the audio cables or RCA
connectors.

For anyone else who encounters this problem, the source was apparently
an RF choke molded into the power lead coming from the fuse and 12v+
wire and just before the on-off switch. Feeding 12v directly into the
switch connector (i.e, bypassing the fuse and choke) eliminated the
noise. Though Audiovox wasn't able to solve my problem, I have to give
them credit for responding quickly to my email and then following up
with an "OK" when I proposed removing the choke.

Can't guarantee the same fix will work with anyone else's system (FWIW,
mine is installed in a 1999 Chevy Express van). Or explain why it
works: the choke was still there in my testing, dangling from the
on-off switch with the fuse and 12v connector wire trailing off it.
It--or the system comprising the choke and a few inches of wire on
either side--apparently generates a signal or acts as an active antenna
when there's 12v across it, but is harmless when connected to the power
lead so long as there's no voltage drop across it.

BTW, the wired modulator is a nice idea: a reasonably easy way to add
an aux. input to a car radio for a DVD, VCR, and/or satellite radio
without the problems of the wireless FM modulators. Sound quality is
good and it completely disconnects the car antenna from the radio when
it's switched on, with no discernable effect on radio reception when
it's switched off. We have a moderately strong station on 89.1 Mhz (one
of the two freqs. it uses to squirt the audio signal into the radio)
but the station is totally inaudible, with no interference, when the
modulator is switched on (unlike the wireless FM modulators that can't
share a freq. with an active station).

  #4  
Old April 22nd 17, 08:30 PM posted to rec.audio.car
external usenet poster
 
Posts: 1
Default Audiovox Wired FM Modulator Whines

On Wednesday, July 12, 2006 at 10:52:25 AM UTC-4, Chip Bearden wrote:
> Just installed my second Audiovox FMM100A wired FM modulator. The first
> one had a high-frequency "whine" (like a carrier tone, but audible)
> even with no audio source feeding the box and with the car engine shut
> off. It's like taking a hearing test at the doctor's office with very
> high-pitched tones. Audiovox tech support said that shouldn't happen
> (the most dangerous words in technology: "it *should* work" followed
> closely by "that shouldn't happen") and advised me to return it. The
> second unit performs identically. It's not that I'm overly sensitive to
> high freqs; the rest of my family hears it, too.
>
> I've tried relocating the ground, feeding power from a separate
> battery, wrapping the loose wires separately, enclosing the whole
> package in foil and connecting that to ground with a capacitor to
> intercept stray RF, etc.
>
> The whine isn't as audible while driving, but it's loud enough to be
> annoying even with the car radio treble turned down a bit. Otherwise it
> works like a charm: when switched on, it routes the audio through the
> car speakers on one of two FM frequencies even if there's a strong
> station on that freq.
>
> Anyone else have this problem? And/or a fix?


I installed the Audiovox FM modulator on my Range Rover and it works correctly intermittently. The fader only sounds out of my driver side speakers despite the fact that the fader is in the middle balance. We have tried changing the RCA cable the problem persists. I tested it with 2 different Iphones and my Ipod and problem persists. I tried changing the frequency from 89.1 to 88.7mhz tyhat did not work either. Anyopne has any suggestions?? Lou
 




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