Rockbox mail archiveSubject: general notes on AJB circuit
From: Andrew Jamieson (ajamiesn_at_mira.net)
Just thought I'd deliver some general info on the AJB HW whilst I am still working on the schematic.
* 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 written to the HD during operation.
* 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 Archos circuit you get a 3dB roll-off point at :
F(3dB) = 1/(2*Pi*R*C)
Where R = (47 + 18) || 1k5 = 62.3 Ohms
Therefore, F(3dB) = 255 Hz !!! No wonder this unit has a problem with bass at low load impedance.
* 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 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!! Maybe I'm just all thumbs, but you have been warned.
Page was last modified "Jan 10 2012" The Rockbox Crew