On Sat, 10 Jul 1999, Garst R. Reese wrote:
>Hi folks,
>Has any brave soul opened up their 380XD and looked at the input circuit
>on line in. I need real LF response for some amplifier testing. I
>suspect I could find the input coupling capcitors and short them out,
>but I somebody has tried this and either succeeded or failed, I would
>like to hear about it.
I don't like the sound of it, Garst. With bigger caps you can overdrive
the sound circuit, but with no caps at all you have all the problems of
polarities, impedances and voltage levels as well. I blew away a motherboard
on a laptop with this sort of messing - floppy, mouse, sound, lpt, & com port
in one glorious zap! Then you want to start testing (READ OVERDRIVING).
Something will die, going on the law of averages.
I gather IBM have rolled off the lower frequencies, probably to protect
the "squeakers" they have on board to hear with. It may also be that tha
SOUND CHIP is set up that way, for tiny speakers. Does it HAVE to be a laptop?
Why not an audio amp? Or a real sound card? Might I suggest playing with a real
toy ;-)?
As an aside, the input coupling caps are only one way of rolling off the
LF, and I expect IBM has used others (like the bass/treble area, and OUTPUT
caps) so I would expect little gain for your pain. You typically have a high
impedance on the input. The effect of a smaller cap (= larger resistance at LF)
is fairly limited, unless you sacrifice quality completely. Not so at the
output, which is low impedance, and the bass/treble area allows them to set it
any way they want. Doubling the OUTPUT caps (if such exist) is the quickest way
to achieving what you want.
--
Regards,
Declan Moriarty
