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Interesting experience with a wall wart

I’ve been experiencing some hum in my system. It’s been going on for a few months. It only happens on the turntable input. Both channels (or all channels) equally. No different when I change grounding wires and/or locations, or when I swap tubes on my Eastern Electric Minimax. I tried changing cables, changing cartridges, grounded and non-grounded power cords. No change. It’s gotten so annoying I’ve stopped listening to vinyl.

Sure I could turn the volume down, and/or ignore it, but it’s an annoying hum.

Today, I got inspired. I pulled the rack forward, and started unplugging things. One by one, I eliminated causes. Finally, I found the guilty culprit. It’s a wall wart. 24V DC, driving the turntable motor – a stock motor from Acoustic Solid. Thing is at least 10 years old. Anyway, I plug it in, I hear the hum. Pull it out, the hum is minimal. This is true no matter where I connect the plug – in the rack, a separate outlet, even an extension cord running from the dining room. I tried shielding it with an aluminum sheet, so I don’t think RF is involved, maybe a magnetic field? Or some electrical frequency that is propagating the the house electrical.

I ordered a new “low noise” AC adapter off of ebay for $25, we’ll see if that fixes it.

Any event, thought I’d share. Open to ideas.

P.S. You can see some pics of my Big Sur turntable in my flickr album.
designdude
designdude OP
23 posts
 
Thanks for the ideas. I don't know if the existing wall wart is switching or linear. I did do some internet research today - my conclusion was that it's not the architecture, it's the implementation.  (although, I was quite surprised at how much the adapter affected the system, even when connected to an outlet in another room). So, I opted for a quick, low cost solution. If it works, yeah. If not, no harm, no foul. 

As far as option B, I think the next option would be a rechargeable 24V battery. 

BTW,  the existing wall wart has an amp rating of 600mA, the new adapter (switching architecture) is rated at 2 amps.   

designdude OP
23 posts
 
Ghosthouse, that is an interesting little device, could be just the ticket. I will keep it in mind in the event that the new adapter is noisy. 

Also, as an aside, I did have another 24V adapter, rated at 220mA. It has no connector, just raw wires, but a check with a digital multimeter shows it is working. When I plugged this adapter into the system (using the the same outlets as above) I could not hear any difference in the hum.

designdude OP
23 posts
 
Also, I hear the hum when I plug the AC adapter into the power outlet - even if the output wire is not plugged into the turntable motor. And the turntable motor itself has no electrical connection to anything else in the system. 

I think the adapter is injecting some noise into the system, as bcowen suggested.

Thus, my next option of a rechargeable 24V battery. 

 
jl35
3,966 posts
 
Walwarts, video systems, streamers, computers ... unplug them all 
georgehifi's avatar
georgehifi
10,312 posts
 
SMP anything is just a HF noise generator. It pollutes everything in your cherished hifi sytem. 

Here a test, get an AM portable radio (without auto mute between stations) tune it down low around 800khz but off station.
And go near any thing that has an smp power supply, even Class-D amps and listen to noise it makes through that radio.

Cheers George 
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