Simple tube question...
Sep 9, 2009 at 2:10 AM Thread Starter Post #1 of 6

JungleMan

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So I'm aware that tubes go bad after so many hours. I've had Mullard M8100 and Ulyanovsk 6S19P-V tubes in my DV332 amp hooked up to my AKG K701 for about a year now. They still sound pretty good though lately I've noticed a hissing sound at higher volumes. If I turn the amp more than about 40% I hear a hissing sound which gets louder as I turn the volume knob.

Definitely isn't a ground loop, I have a Xitel Ground Loop Eliminator and I tested with a 3-to-2.

My question is, one, do you think the tubes being old is causing this? And secondly, which set of tubes would it be, the driver tubes (Mullard) or power tubes (Ulyanovsk)? Thanks... I'd rather not buy two new pairs of tubes if just one pair needs to go. Thanks.
 
Sep 9, 2009 at 2:20 AM Post #2 of 6
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Usually the volume control is a voltage divider at the amp's input, before any of the active devices. In these cases, a hiss or hum proportional to the volume setting indicates noise from the UPSTREAM components. Noise on the amp's part would be constant and independent of volume setting. Btw, a hiss does not normally indicate a ground loop - a hum or a buzz does.

What are you using for source, and do you have any other sources you could use for comparison?
 
Sep 9, 2009 at 2:21 AM Post #3 of 6

bergman2

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it doesn't sound like a tube related issue to me ... is the hissing a new problem or has it been around awhile?
 
Sep 9, 2009 at 11:13 AM Post #5 of 6

JungleMan

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Actually don't know why I didn't think to try another source, just didn't think the source was the problem I guess. My source right now is my desktop computer (Creative Audigy 2 ZS); plugged in my iPhone and sure enough, not a single hiss even at maximum volume.

I was inclined to think "tubes" because the original tubes in this amp were causing a hum, which these new tubes got rid of (as well as drastically improving sound quality)

A few things have changed recently; I added a Wi-Fi dongle to this computer as well as an extra video card, and I also moved to a new house in July, so any one of those may be causing the issue. When I get back from work today I'm going to try installing drivers for/plugging in to the onboard sound (gag) and seeing if I can at least get it to not hiss, then maybe messing with the Wi-Fi or second video card. Any other things I should try?
 

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