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Subject: Re: general notes on AJB circuit
From: Eric Linenberg (elinenbe_at_umich.edu)
Date: 2001-12-14


It seems the Archos writes a few things to the hard drive which in the
long run make the player better/worse depending on the case. I am
assuming this is done by just having some blanks data space in the mod
file that the Archos can write to. But, then wouldn't the checksum
change? If this was the case, then the checksum would have to be
recalculated every time a write takes place. You can see this
behavior in action when you change the volume on the player and you
have to wait for the drive to spin up, so it can save the value, thus
the delayed action. I think it would be much better if it were to do
this at shutdown, not only making the device operate more smoothly,
but also increasing the battery life at the same time.

-eric

AJ> Just thought I'd deliver some general info on the AJB HW whilst I am still working on the schematic.

AJ> * During the whole time I've been buzzing this thing out, it has remembered the last song played - this without attached batteries. Therefore, the status of the currently played song must be
AJ> written to the HD during operation.

AJ> * The value of the caps on the output circuit is only 10uF (which is still kinda impressive for a 1206 based ceramic, but I digress ...). Therefore, with 18 Ohm buds and the stock standard
AJ> Archos circuit you get a 3dB roll-off point at :

AJ> F(3dB) = 1/(2*Pi*R*C)

AJ> Where R = (47 + 18) || 1k5 = 62.3 Ohms
AJ> and C= 10uF

AJ> Therefore, F(3dB) = 255 Hz !!! No wonder this unit has a problem with bass at low load impedance.

AJ> * For those of you wanting to take the unit appart to get at the LCD or Backlight, I gotta warn you - it can be a bastard getting the zebra stripe (little rubbery thingie that connects the LCD
AJ> to the PCB) connected again. TJ didn't seem to have any problem with this when he did his blue backlight mode, but I spent about 2 hours trying to make my LCD work again after disconnecting it!!
AJ> Maybe I'm just all thumbs, but you have been warned.



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