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Subject: Re: Line out vs headphone jack
From: Michael O'Quinn (michael_at_oquinn.info)
Date: 2003-04-01


On 31 Mar 2003, Bradley Alexander wrote:

> Hi all,
>
> Got a problem with my JB6000. I was playing it in the car and all of a
> sudden, I heard a pop (like a pop on an LP), and the right channel
> started playing with nearly no output, with garbled peaks. I switched to
> the headphone output and it was normal.
>
> This brings up several questions. First, are there separate channels
> between the line out an the headphone out? I have not yet taken it apart
> (I have a talk to give at our LUG this weekend, perhaps after that), but
> I am trying to isolate the problem. Is it possible/likely that the jack
> went bad or more likely that something on one of the boards went out?
>
> In the interim, since the headphone jack is working, what volume level
> would work best to not blow out the input section of my tape deck? I set
> it at 50%, and it seemed to work. Should I set it lower?
>
> Thanks,

Are you sure it's the Jukebox and not the car stereo? Have you tried
plugging something else into the line out jack to see if it works? I just
plugged some headphones into the line out jack, and I heard the music,
although not very loud. But it was enough to verify that the signal was
present in both channels.

In general you won't burn anything out connecting the headphone output to
a line input. In fact, I do it all the time. I have an amp that is a
good amp, but it's input is not terribly sensitive, so the extra boost
from the headphone amp in the Jukebox (such as it is) give the input stage
of the amp a signal more to it's liking.

The voltages are actually pretty close. The difference is that the
headphone jack is (a) adjustable, and (b) capable of supplying more
current, and (c) capable of supplying a slightly higher voltage signal.
Since a line input has a high impedance, it draws very little current from
either output jack, so there's no problem. The signal will become
horribly distorted before it gets high enough to damage your equipment.

You can test if it's the jack by just wiggling the plug while it's
playing. If you hear anything, even just crackling that changes as you
move it, I'd suspect something mechanical like the plug, jack, or cord.
OTOH, since you heard a sudden pop out of the blue, followed by a dead
channel, I suspect something is most likely blown.

Michael



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