High THD...sometimes...
Mar 14, 2006 at 8:58 AM Thread Starter Post #1 of 1

goandeatsomestuf

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My main (only) computer station is surrounding an Acer Ferrari 4005 laptop. For some time it has been doing fairly well, amplifying my headphones well-enough through a USB line-out of sorts (Griffin iMic).

At any volume level, there is audible and ANNOYING distortion that is probably close to 10%, but it is only noticeable (to my ears, at least) when using my speakers, not any of my headphones (HD280 and ER-6i). My DVD player (JVC VX-N50) produces worse output under any configuration (save optical/coaxial digital outs; i have no method to use or test these at the moment). By comparison, my iPod has a pristine out, with little to no distortion above that introduced by the preamp, and even my XBox has less exponentially less distortion than the laptop and DVD player.

The strangest thing is the distortion persists through powered USB connections on the laptop; connecting my iPod to the computer translates the distortion present in the laptop's headphone/SPDIF-out and iMic to the iPod, causing it to emit the same distortion as if it were an audio-out of the computer as well. Removing the iPod from the computer results in a once-again clean connection (even though it was charging on "dirty" power... which once again baffles me)

To say the least, this is lame. Really lame. I'm not too sure how this all persists through the preamp and amp yet not through headphones, but I'm not too happy with it. To note, I'm using fairly high quality interconnects and (at the moment) any other power sources besides those mentioned are not significantly present around the system.

Layout:
Ferrari 4000 running off of wall power, connected to an external HDD, external mouse, Griffin iMic, ethernet cable, DVI cable to monitor
iMic -> 1/4 -> 2x RCA -> NAD 1130
NAD 1130 powered off of surge-only protected outlets of an APC XS1000 uninterruptible power supply. NAD sending signal to powered amplifier via normal outs, to powered subwoofer using high-level outs (15V per specifications, untested)

Things I know:
-The distortion is not due to the preamp or amp, each has been tested individually.
-The distortion has been routed down to the laptop and connected peripherals.
-The distortion persists through any peripheral attached to the laptop via any digital or analog connection known.
-The distortion cannot be detected on headphones.
-Unplugging the laptop does nothing
-Turning off the LCD does nothing
-Disconnecting the external hard drive is not an option (that's where all the music is
smily_headphones1.gif
). Disconnecting the DVI is highly unfavorable.

Things I don't know:
-Whether or not a USB-based DAC, or any output, for that matter, is capable of eliminating this problem, either by using an outboard power supply or ignoring the poor grounds in the laptop.
-If the distortion persists through the PCMCIA slot.

This is where your advice comes in, because at this point I have no idea what to do, since the two components I would have thought most likely to be of decent quality (computer and DVD player) and carry the majority of my media have now failed me. Thank you for any advice in advance, or even for reading this far.
 

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