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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

Showing 1 response by bcowen

bcowen
68 posts
 
The power feeding a turntable motor can have a profound effect on the resulting sound.  Most wal-warts are switching supplies, and as Ghosthouse notes, can inject a lot of noise into the AC....which affects everything in your system.  You should really consider a linear power supply which will likely pay some nice dividends, and beyond just the sound of your analog rig.  Yup, way more than $25, but if you are a DIY type person there are some nice kits that can get you going for around $200. 

Also, be sure the wal-wart you just purchased can handle the amp draw of your motor.  If not, either it or the turntable motor itself are at risk of an early demise.
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