Tube amplified computer audio: how to kill the hum?

[erichayes]

Well, here are the numbers for the RS unit--only one minor surprise.

Unit tested:
Radio Shack #270-954

Test equipment:
Tektronix SG-505 signal generator
Tektronix AA-501A audio analyzer

All measurements referenced to 1dBM (600Ω), 1kc. Residual distortion (0.0027%) has been factored out.

Insertion loss: -0.3 dB both channels

Frequency response L/R:

10~ -5.5/-5.6dB
20~ -2.9/-3.2dB
100~ -.6/-.6dB
1kc 0/0dB
10kc +0.2/+0.2dB
20kc +0.3/+0.4dB
30kc +0.6/+0.6dB
40kc +0.9/+1.0dB
100kc +6.0/+6.7dB

THD @ 1kc 0.084/0.09%

I don't know if the response curve was intentional on Radio Shack's part (I doubt it) or not. In any event, it appears that this product is aimed at the "medium-fi" market that wants a band-aid cure for the symptom, rather than the serious audiophile looking for a cure for the disease. Mind you, I'm not faulting the product. For 17 bucks, it does an admirable job of performing its intended function: remove hum. I'm reiterating with test results what Tom said: Don't expect fantastic results if you choose to go this route.

Edit: My Sound Tech 1510A analyzer started throwing error codes at me this afternoon. I'm going to try kickstarting my somewhat senile 1500 and try to get pictures of the response curves from 20-40,000 cycles posted.

[Geek]

Looks like a darn spectacular band aid for $17 if you ask me :)

Cheers!

[TomMcNally]

Thanks for the lab tests Eric.
They are actually better than I guessed.
I figured the repsonse would be way down at
100 Hz ...

I wouldn't use one in line with a high quality source,
but to couple a computer, which has a sound card
with 79 cents worth of parts in the output stage, it's
fine !

[wiredbecker]

very cool, thanks guys