Crackling noise

[Raphaz]

Hello fellow Audiokarmians,

I get crackling, scratching noises, on both channels, on both receivers.

It's not constant, just every now and then. It can be dead quiet (when nothing is playing) for half an hour and suddenly, without me touching anything, it goes... "chrrk cr crkck chg chk" a couple times, then it's quiet again for 10 min. or an hour, then it comes again, and so on, no clear pattern. It's not super loud.
It also happens sometimes when music is playing – it sounds like a loose contact (scratching, popping, distortion, and short outings), usually only in one channel, not constantly either.

I checked all cables and speaker wires. That doesn't seem to be the issue.
Could it be some dials/knobs on one of the receivers needing Deoxit or WD40? But if so, wouldn't the crackling only appear when I actually turn some of the knobs?
Can it be the power outlet? I'm in a very old industrial building and electricity is a bit of a mystery. Sometimes the lights go dim for a sec when I turn on one of the receivers, or when the A/C comes on. If that's the issue, do I get some sort of power conditioner or something like that between outlet and receivers?

Any ideas on what's causing this?
Thanks!

–––––

Yamaha R-2000
2 x KEF Q500
1 x Klipsch R-112SW

Nikko NR-1219
6 x Minimus 7

MacBook Pro (mainly Spotify)
Technics SL-D3
Nakamichi LX-3
Some Denon CD player

 

[Raphaz]

After running the R-2000 alone for a day, no noise. So we can probably exclude that from being the villain.
Turning the Nikko on and off a couple times makes me think that the issue is coming from the Nikko. For some reason the noise is hearable on the Qs when the Nikko is on, even though the Qs are hooked up directly to the R-2000, and the latter feeds into the Nikko which then powers the Minimus' go figure.. .
I opened up the Nikko and cleaned and deoxed all the knobs, specially the power on/off. Now there's less noise, but standing close enough to the speakers I can still hear it, less obvious/loud though.

What's happening here?

 

[titanstats]

After running the R-2000 alone for a day, no noise. So we can probably exclude that from being the villain.
Turning the Nikko on and off a couple times makes me think that the issue is coming from the Nikko. For some reason the noise is hearable on the Qs when the Nikko is on, even though the Qs are hooked up directly to the R-2000, and the latter feeds into the Nikko which then powers the Minimus' go figure.. .
I opened up the Nikko and cleaned and deoxed all the knobs, specially the power on/off. Now there's less noise, but standing close enough to the speakers I can still hear it, less obvious/loud though.

What's happening here?

Hard to say without fooling around for a while. Is it an external noise caused by stray RF, like a dimmer switch or an appliance, even a neighbour with a radio rig? Or is it an internal noise, say as from faulty transistors?

Those would be the two things I’d try to decide on first. Stray RF can find its way into gear many different ways, and certain vintage transistors will start to make a very particular noise when they are failing, almost like a faint Morse code of noise.

 

[cademan]

FYI, crackling in one channel is usually a noisy signal transistor in that channel. USUALLY!

 

[Raphaz]

Hard to say without fooling around for a while. Is it an external noise caused by stray RF, like a dimmer switch or an appliance, even a neighbour with a radio rig? Or is it an internal noise, say as from faulty transistors?

Those would be the two things I’d try to decide on first. Stray RF can find its way into gear many different ways, and certain vintage transistors will start to make a very particular noise when they are failing, almost like a faint Morse code of noise.

Thanks. Not sure what to make with yours and cademans comments.

I’m not a tech guy but could it be something that is on the same power line like the outlet that the receivers draw power from? As mentioned the electricity in this building is weird. If that’s the case, would a power conditioner or something like that take care of this, by cleaning/filtering the power before the receivers? Does that even make sense?

if it’s a transistor that picks up external stray RF, how can I determine if that is the case and if so how can I find out which transistor it is? And once I know, can I bring it to a tech to swap the transistor? Or can I shield the receiver or certain parts from external stray RF? How?

 

[titanstats]

If it's the transistors, they need to be replaced as the problem only gets worse over time; they're old now, and many have a known issue where they corrode over time and start getting noisy. Lots of different vintage brands have the problem, Marantz and Akai gear have lots of 'em inside but they're not alone.

If it's RF, you're playing a detective game where something in or near your home is making noise and you have to hunt around to find out what it is. Dimmer switches, fridges, ballasts, all sorts of things can do it. I had a weird ghost once that took me quite a while to find -- in the end it was an intercom transformer box on the inside of a closet hidden at the very top of it. One of the external walls of the closet was a few feet from my stereo at the time, and it had no problem broadcasting the few feet required. It's at least a possibility worth looking at first, as it doesn't require troubleshooting/repairing the receiver.

I'm kinda suspecting transistors though, just because of the age of the unit, but you know how opinions are.

 

[wmgwizard]

I have experienced similar issues and found dirty bias trim pots can be the issue.

From your description of your technical ability I would recommend professional or at least experienced assistance as setting the bias wrong after cleaning the pots can lead to significant damage or failure.

 

[Raphaz]

Thank you all. Sounds like I have to bring it in.