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Subject: RE: Getting rid of that damn noise.
From: Bryan Sivak (
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
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
By the way, this is quite interessting. Two outputs of this device are
to GND, to inputs are left unconnected.

> BTW: with no direct feedback from the switcher output to comp, there
> 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
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
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,
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
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
(I know, the solution is a bit unprofessional, but it works for me ;-)


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