Tube amplified computer audio: how to kill the hum?

[wiredbecker]

Increasingly, my audio source consists of downloaded mp3s or streaming web audio from my computer. Tom mentioned that there were some workarounds for killing computer related hum. Anyone have any leads on a how to? I'd love to run everything through my Darling or ST35 without that dadgummed hum

[sorenj07]

try bypassing ground pins for various components that plug into your computer. if you find floating voltage on things like digital cameras etc. after plugging them into the usb, you should re-ground the computer at one point, and try lifting the ground between your amp's signal/chassis and earth.

[Geek]

Hi,

After months of driving myself insane with the same problem, I broke down and bought an inline ground-loop isolator - fixed! Yellow_Light_Colorz_PDT_16

Cheers!

[mesherm]

http://store.xmfanstore.com/gli.html
http://www.radioshack.com/product/index ... Id=2062214
http://www.provantage.com/xitel-gli1-x1~7XITL004.htm
http://www.ramelectronics.net/html/GLI1-X1.html

[wiredbecker]

Thanks guys.

[TomMcNally]

Just so you guys know ... those things contain a set
of cheezy little transformers that do the isolation.
I only have personal experience with the Radio Shack
device - and while it does work just fine, and has a
nice 1/8" stereo adapter included, the audio quality
for you purists is far from good. The freq response
is probably 100 to 10,000 ... the price of a set of good
transformers would be a lot more than $ 16.95 or
$ 34.95 ... so keep that in mind.

Thanks for all of the links Mike !
I have one here on my system - now I wish they would
come up with something for RS-232 so the connection
from the PC to the Polk XM Tuner wouldn't cause a
nasty ground loop !

[wiredbecker]

hmmm any chance an isolation transformer would do some good here?

[TomMcNally]

Sometimes you get lucky - if the amp and the computer are plugged
into the same outlet it may not hum at all. Like Soren suggested,
try lifting the ground on the amp with one of those old-fashioned
3 prog adapters - just don't ground the ground. The amps own
power transformer IS an isolation transformer, BUT - the chassis
is grounded to the audio - as it in in the computer ...

It's best to leave the computer grounded and unground the amp -
as it's not a real safety hazard (no flames please - haha)

... tom

[wiredbecker]

haha good one Tom

unfortunately, the computer is plugged into a UPS backup... I guess I could try running the amp on that as well. Or plugging both directly into the wall outlet. All stuff to try.

[TomMcNally]

You can't go wrong trying the Radio Shack ground isolation
thing ... it's only $ 16.95 and is very handy for messing
around anyway.

[Geek]

The Radio Shack one is the one I used and as long as the source resistance is really low (100 ohms or less, like a soundcard or other SS source, even an ECC88 in a WCF configuration as a linedriver [~180 ohms] does good), there's little loss.

[erichayes]

Now that my sight's getting good enough to start resuming bench work, I'll pick up one of the RS units tomorrow and run it through its paces. I'll report back tomorrow afternoon.

[mesherm]

Tom, here is a link to an RS-232 optical isolator.
http://www.pcconnection.com/ProductDeta ... ku=5202496

[TomMcNally]

Thanks Mike ...

Have you seen a schematic for something like that ?
I'd rather build than buy.

[mesherm]

http://www.delabs-circuits.com/png_circ ... 60115.html
http://chaokhun.kmitl.ac.th/~kswichit/R ... Rs232.html