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Subject: Re: Getting rid of that damn noise.
From: Rob & Liz Ward (wards_at_paradise.net.nz)
Date: 2001-12-28


Agreed. C14 delays power off.

Rob

----- Original Message -----
From: "Joachim Schiffer" <gemoin_at_gmx.net>
To: <jukebox_at_cool.haxx.se>
Sent: Saturday, December 29, 2001 1:20 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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