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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
nagel
48 posts
 
I have an ifi dc pur, and it is nice, helps the sound quality whether feeding my startech rex or uptone audio regen when fed from their wallworts. I do still plan to buy LPS for all of my dc powered devices for the reasons stated. I've also learned that R-core transformers are the best. I highly recommend the LPS links at head-fi and the ultra usb link at usaudionmart. Lengthy reading and different on the bleeding edge, but lots of useful info there. My system has never sounded better, and I expect many more cost effective upgrades in the near future.

https://www.head-fi.org/f/threads/audio-power-supplies-part3-smps-lps-supercap-battery-diy-route-new...

http://www.usaudiomart.com/forum/viewtopic.php?f=35&t=1172&start=1710

I don't think the DC Pur is the solution to your hum problems though. If the PS replacement doesn't solve it, maybe your turntable motor has issues.
designdude OP
23 posts
 
Well, some interesting developments on the hum issue. I got the new "low noise" power supply today (switching mode), and yes, it adds AC noise to the line, even more than the old wall wart. I got a little frustrated, and went on a power mission. I went through the house, and unplugged as much as I could find of AC/DC devices, including everything in my office, battery chargers in the kitchen, devices around the TV, you name it. I then unplugged everything in the audio system except the amplifier, (a Sony STR-DA5600ES), and the phono preamp (an Eastern Electric Minimax). On every input selection, the system is dead quiet, but when I set the input on the receiver to the phono preamp, there is just a taint of a hum. The hum is faint. (and yes, I have tried all kinds of variations of grounding wires between the turntable, the preamp, and the receiver, and while some are better than others, there is always a faint hum. You can only hear it when your ear is say 6" in front of the speaker, but it's there).  When I connect the wall wart that powers the turntable motor, there is a jump in the hum. There is also a slight jump in the hum when I plug in my Olive Musica server - not as much as the wall wart, but a jump nonetheless.

Again, the hum is only present in the phono circuit. So, my conclusion is that there is either some AC noise in the line, something in the Minimax, something in the cartridge (Shure V15VMXr), or something in the cables - and that something is getting amplified. 

I don't have any kind of power conditioning or power filtering, just a WireMold power strip. I do have some good cables in the system, but at this point, I don't think cables are the issue. 

Open to thoughts. 



designdude OP
23 posts
 
THE HUM IS GONE!

Took a little effort. First thing I did was buy a Ebtech Hum Exterminator. I plugged the power cord on my Eastern Electric Minimax into it. 90% of the hum was gone.

http://www.ebtechaudio.com/humxdes.html

There was still a very faint hum at higher volumes. Worse yet, when I would touch certain things (the motor housing, the tonearm, the phono adapter) the hum would increase. Made me think grounding wasn’t right.

Turns out there are two ground screws on my Cardas phono adapter. Even thought they both connect to the main body (aluminum, black anodized), I don’t think they are perfectly grounded. I moved the ground wires to the same post and everything is fine. Dead quiet.

http://www.cardas.com/phono_box.php
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