Rockbox.org home
release
dev builds
extras
themes manual
wiki
device status forums
mailing lists
IRC bugs
patches
dev guide



Rockbox mail archive

Subject: RE: Getting rid of that damn noise.
From: Justin Fisher (JustinF_at_valvesoftware.com)
Date: 2001-12-27


The noise is always present and a constant volume, regardless of whether the
vol is up or down. It's just very hard to hear when the vol is up.

Also, the noise is not a constant ripple - it exactly matches whatever the
LCD is actually _doing_ (you can actually control the noise by changing what
the LCD is doing), eg it's whether something is being changed or updated
onscreen. Thus I'm pretty sure that when the HDD reads and the screen
freezes, it's silent because the LCD stoped updating, not because of the
HDD. The HDD doesn't explain all the other links with the LCD.
I'm guessing that this rules out voltage inverters (they would be linked to
power drain such as HDD, not to the LCD screen), and also seems to rule out
the LCD's power supply, clock, etc, as these things would all produce a
constant hum or whine, which the noise isn't.

Turn the volume right down so you can hear the hum, then start browsing
menus. then go back to the level-meter screen. You'll see what I mean - the
noise is directly tied to what is visibly changing on the LCD, not an
underlying constant.
Particularly with the level-meter, which updates constantly at a lowish
frequency (4hz?), the hum is replaces by a pulsing at that frequency and
remains constant with the updates until they freeze.

I don't see how these things can be explained by something outside the LCD
system. No component (other than the CPU) has it's state affected by what is
actually displaying on the LCD, and you can control the noise by controlling
what is on the LCD.
AFAICS, the buck stops at the LCD system.

-----Original Message-----
From: Rob Ward [mailto:wards_at_paradise.net.nz]
Sent: Thursday, December 27, 2001 11:55 PM
To: jukebox_at_cool.haxx.se
Subject: Re: Getting rid of that damn noise.

If you can hear the whistle with the vol right down, then it is probably a
switching regulator. Ofter the chokes (inductors) on these whistle at maybe
5-10kHz, but as you say, the whistling disappears as the load increases -
this is because the duty cycle (or sometimes frequency) changes as the load
varies. What voltage do you need to drive the HDD? Is it 12V?

Rob

----- Original Message -----
From: "Tjerk Schuringa" <regenpak_at_yahoo.com>
To: <jukebox_at_cool.haxx.se>
Sent: Friday, December 28, 2001 2:52 AM
Subject: Re: Getting rid of that damn noise.

> I observed two things about the whistle: it is also present with the
volume all
> the way down and it does cease when the HD spins up in my newish (used to
be
> heehee) unit. I haven't looked at the schematics yet but it could be that
one
> of the voltage inverters (there must be several!) that feeds the HD goes
into a
> sort of "burst" mode which is about 1 kHz (that irritating whistle) and
goes to
> an ultrasonic frequency when the HD draws current. It's likely to be a
messy
> mod in any case!
>
> T.J.
>



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