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Subject: RE: Getting rid of that damn noise.
From: Bryan Sivak (bryan.sivak_at_electricknowledge.com)
Date: 2001-12-28


While I know nothing about all this hardware hacking you guys are doing (but
i think it's pretty damn cool), one other piece of info that might be useful
-- when I plug my AJR into my car stereo, and use it with a car charger
plugged in simultaneously, the background whine (which is difficult to hear
if you've got the thing turned up loudly) becomes an incredibly annoying,
high-pitched squeal. I've never tried the test while the jukebox is plugged
into the wall, but i'm guessing the same thing might happen. Although I
suppose it could be something with the charger itself (?)...

Anyway, thought that might be helpful...

-----Original Message-----
From: Joachim Schiffer
To: jukebox_at_cool.haxx.se
Sent: 12/28/2001 4:20 AM
Subject: Re: Getting rid of that damn noise.

> The 10k resistor (on the high side of T3 and the 34063 supply) seems
to be
> the current limiter for the battery charger.

Oops. First mistake. Thank you :-)
It's a 0.47 Ohm Resistor. You're right, 10K is a bit high...
Sorry, as I said, there might still be some Bugs :-)

Second mistake, I found: note 2.) must be named note 1.) on U13C and
U13D.
By the way, this is quite interessting. Two outputs of this device are
connected
to GND, to inputs are left unconnected.

> BTW: with no direct feedback from the switcher output to comp, there
is
> absolutely no voltage regulation; the switcher is being used more as a
> current source than a voltage source.

I hope this is not because there is a connection missing...
But I didn't find additional connections in this area.

Because of the behaviour of the recorder, when turning off the power,
i think there is also something missing in the part of the circuit
around
Q11, Q12, C14. I think C14 is responsible for the delay when powering
off the unit, but there has to be at least an additional resistor, if it
was
that way. But i didn't find one...

As I said, the schematics are only almost complete ;-)

Regarding the noise, it's still there when you turn off the backlight,
and
even if I disconnect the LCD completely. I think the power generation
(neg. voltage for LCD) is done by the built-in driver chip itself.
Otherwise I can't explain all the caps, which are conneted to it.
So the power generation in the LCD can't be the trigger for that noise.

BTW, I have a simple solution to increase the signal to noise ratio ;-)
I have headphones with a volume regulator. When I turn the volume
down on the headphones an up on the player a bit, i can't hear the noise
anymore, even if i hear silent classical music.
So if nothing helps, i think, a modification of the output filters to
reduce
the volume a bit, so that the volume of the player must be turned up a
little, would reduce the noice. In my opinion, the recorder is loud
enough...
(I know, the solution is a bit unprofessional, but it works for me ;-)

/Joachim



Page was last modified "Jan 10 2012" The Rockbox Crew
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