strange sound from my Threshold SA3 sometimes

[Tino]

Hi guys, my SA3 once in a blue moon (and more so recently) makes this roaring wind type noise but from only the left channel. It will play music through just fine but there is this noise present. It usually passes on its own. I cant recall if it does it more when its first turned on or not. Also it doesnt mater if there is any input on the back or not. I can disconnect the RCA cables and have the same result.

Here is a video with audio so you can listen. You might have to right click and "save as" and dump it on your computer if you experience any codec issues. It does that on some machines. Once saved locally, its hould play fine.

Any suggestions welcome as to what it could be.


http://powerthings.com/pics/noise.wmv



PS. I can swear that I heard this noise once through my creative computer speakers but faintly and it was also facing the same direction so for example if the left channel on the SA3 is facing south, it was whatever side on the computer speaker that also faces south. Doesnt make any sense I know...

[analog_sa]

Originally posted by Tino
the left channel on the SA3 is facing south

A chat with a Feng Shui specialist could sort this out but before that i would replace all tantalum caps and inspect the boards for cold solder joints.

[Nelson Pass]

Could be a bad Zener diode, or maybe a bad transistor, or maybe
oscillation.

[Bakmeel]

If I turn down the volume of your movie a bit, it sounds just like the failure I had with my Aleph 2. You're describing a wind-like hiss while audio is playable. This is exactly the effect I could hear.

It turned out to be a broken Zener in the current source supplying the input differential pair.

I suggest you stop playing music with your amp. I'm not exactly familiar with the Threshold topology, but for my case Iwas lucky the failure didn't escalate into a large DC on my output.

Good luck!
Bakmeel

[Tino]

Thanks for the replies See the crazy thing is that the amp is working perfectly right at the moment with no noise.

Its such an intermittent thing. Maybe once every few weeks it will do it. Can it still be a diode or transistor? I would assume such a failure would be consistent no?

Thanks

BTW when the noise is there, it does not go up in volume when I raise the volume level and the music that would come through sounds perfectly clear. That is of course when it does happen which is once in a while for a few minutes and then just goes away.

[Bakmeel]

Yeah I used to think failures would normally occur only as a kind of true or false state... Turned out to be not quite the case.

I found out semiconductors, or at least zener diodes can have a quite particular failure, that causes them to drift.

Depending on the rest of the circuit (as I don't know the Threshold schematics) it causes funny effects that may or may not appear just depending on the weather or who knows.

Have a look here for my "discoveries" on zener failures.

Good night!
Bakmeel

[Tino]

Man that sucks. Well time to find some place in Toronto, Ontario or the Durham region (again in Ontario) that know how to fix Thresholds well.

...anyone know

PS. Thanks everyone for the replies and help. I love this amp and it must stay for ever. LOL