Declan Moriarty wrote:
>
>
>
> 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
Thanks Declan, I figured I would hear from you:) I agree with all you
say. In fact I don't use input caps either. I was hoping someone had
been into this particular box. I'll be sending you some stuff privately,
but I've been procrastinating, and yeah, busy.
Cheers,
Garst
