2. amps-preamps
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120hz hum coming from all-tube system - but only at high volumes

I generally listen to my system at 8-9olcock on the volume dial.  A friend and I were pushing the dial up to 11-12 oclock and a fairly loud 120hz hum would start to appear after a while.

Bringing the dial back down would eliminate it.  You could then pushing it back up and it'd be fine for a bit and then then hum would reappear.

Do I have bad tubes somewhere?  Ground loop that only rears its head occasionally at high volumes?


(System is Manley Steelhead pre, Manley Mahi's mono amps, Forman Elite-15 PFi power conditioner, schiit yggdrasil DAC, Klipsch Forte IV speakers)
otherones
millercarbon's avatar
millercarbon
12,531 posts
 
If it was there all the time and only became audible at high volume then I would say it is just the way it is, perfectly normal run of the mill noise, and you can track it down if you think it is worth it. But "occasionally" and "fine for a bit" then reappears indicates to me this is heat or power related. Could be a tube, could be something else, but more than likely not right.   

Since you run mono then if it is both then probably not the amps, but more likely the preamp.
audition__audio
1,522 posts
 
First you need to be aware of the difference between a hum and tube/system noise. To me at least the 2 are not easily confused. 

Usually microphonics is a ring or a howl, but to be certain tap around your components to see if the tapping transfers.
elliottbnewcombjr
5,610 posts
 
I suggest you get thee a simple tube tester to help diagnosing this problem and have for the rest of your life

https://www.ebay.com/sch/i.html?_from=R40&_nkw=tube+tester&_sacat=0&LH_TitleDesc=0&_...

make sure you get the manual or can download it.

I am going to part with my 157, works just fine, I recently bought it’s bigger brother 257. tested my preamp’s 17 tubes on both to confirm, they agree with each other on their meters. 

seller says this one has problems, just to show a 157

https://www.ebay.com/itm/274957651485?hash=item4004c0ce1d%3Ag%3APQUAAOSwHeZhS3Ng&LH_BIN=1

this 257  to see it, this one also has comments

https://www.ebay.com/itm/393411222024?hash=item5b9922da08%3Ag%3Aki4AAOSwcXhgzNw-&LH_BIN=1


ghdprentice
7,267 posts
 
60 cycle… I am thinking is what you mean. All ground loops I have experienced have been at low volume or almost none. It is a trickle behind the scenes and does not increase in volume… it is like a, well little trickle of water behind the scenes. So, I don’t think that is what it is.
dill
2,543 posts
 
Pull the power conditioner out of the system and listen for the hum.
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