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Am i receiving alien transmissions?
June 18, 2014 3:48 PM   Subscribe

So i finally got my turn table hooked back up and got a phono preamp. Awesome! But now i'm having mysterious interference, and receiving radio signals on it(!?!?)...

So a while back around black friday i upgraded to The 21st Century, and bought a fancy pioneer network receiver to go with my "smart" tv and other futuretech gadgets. It rocks and i've been pretty impressed with it, but it didn't have a phono preamp. It took me tons of foot dragging through other money obligations and just general procrastination to finally get one, but i just did recently.

So i hook it up, connect the ground wire, and use some really nice heavy-gauge RCA cables to run it into one of the random assignable RCA inputs on my receiver. Fire it up and... it sounds pretty good. The preamp isn't amazing, but it's good enough for casual listening until i get somewhere to set up my dedicated phono system...

And then i noticed a weird "rumble" noise. It persisted even if the turntable was completely off(it's a technics 1200, so it has a power switch). Upon turning up the volume a lot on the receiver, i realized not only was i picking up a constant "bupbupbupbupbupbup" type sound, but also the radio.

At least part of the rumbling seems to be from my wireless router, which it's within a few feet of... but the further i move it away from that the more other interference i pick up. There's no position within the reach of the cables that doesn't either have lots of talk radio and other interference, or lots of rumbling/rhythmic popping noise.

So what do i do? how should i position this thing? does it need to be in a lead box? Is a 6 foot RCA cable too long and somehow acting as an antenna? I've never had a problem like this in the past when i've had receivers/preamps/integrated amps that had a built in phono stage which i just jacked straight into. Is this preamp just crap?

The preamp by the way, is basically this one by MCM, but MCM branded. I'm totally open to buying another one if this one sucks and am open to suggestions. I just planned on using this one until i had more cash laying around... But this is infuriating.
posted by emptythought to Technology (10 answers total) 1 user marked this as a favorite
 
I've had a similar issue with a different set-up when my cords are too long and pick up radio transmissions. Yes, infuriating.
posted by quince at 4:05 PM on June 18


I think it's your RCA cables.

There are shielded ones.
posted by jamjam at 4:14 PM on June 18


Yes, shielded cables are the best solution. If those are not sufficient, cheap ferrite choke cores have solved RFI problems for me, though this requires experimentation.

The bupbupbup noise I've heard from external power supplies. You might systematically unplug items and turn off lights to see if the absence of a device on the same power circuit cures or changes the noise. For a power wart for the audio equipment itself, look for a substitute with the same voltage, current or watts, and polarity, and experiment.
posted by gregoreo at 5:15 PM on June 18


Six foot is a long run for unbalanced audio, particularly in an electrically noisy environment and particularly if that is the cable from the turntable to the pre-amp. The cable is in fact acting as an antenna, the radio you hear will be AM.

If that cable run is between turntable and pre, move your pre closer to the table, six foot is far too long. Turntables output extremely low level signals and your pre is very high gain, it amplifies very low level noise as well as your music signal. Six foot of cable will pick up a lot of noise...

If that six foot run is line level out of the pre you are in better shape. As said above, upgrade your cables, use ferrite beads but also make sure you haven't created a ground loop. Experiment with disconnecting the earth on the turntable (this can make things a lot worse though - so no guarantees) and very much make sure that all of your audio equipment is fed from one power outlet only (a pair together on the wall is normally fine and is near enough to being electrically one outlet).
posted by deadwax at 5:40 PM on June 18 [1 favorite]


Oh, one other thing. Your existing RCA cables are almost certainly shielded, I don't think I've ever found one that wasn't and I've made a lot of cables. Of course, the quality of the shielding does vary.
posted by deadwax at 5:44 PM on June 18


to clarify a couple things:

1. the long cable run is out of the pre to the receiver, not from the turntable to the pre(that's using the stock tech12 cables for now). It's a pretty nice 90s-ish set of monster RCA cables, and if they're not shielded i have no idea why they're as thick and stiff as they are(this is back from when monster sort of made real stuff, they're from an old school home theater setup). They look like a thicker version of the ones linked above.

2. it's all being fed off of one outlet, and through a sort of decent power conditioner(also 90s monster stuff...). i've had ground loop issues with previous equipment here before(and power quality issues) which i sorted by both switching everything to one outlet, and through that power unit.

3. the bupbup noise is definitely interference from my airport extreme. i've process of elimination'd that one out. it's just that nothing else i own picks up that interference, including analog stuff. That thing used to be within inches of my 70s harmon kardon amp and... nothing. although that thing has some of the fattest filter capacitors i've ever seen in anything.

I've just never gotten this kind of interference on any other gear i've used, and i've had some pretty janky, cobbled together, sketchy setups. Like stacks of adapters and cables christmas-storied together on top of piles of junky gear and the power supplies therein all jammed in a tiny space.

I'll try a ferrite when i get home, i have some random ones around in my office i can snap off of unused cables. i'll also try shortening the runs as much as i can and tucking the pre either behind the receiver or next to the turntable instead of on the floor...
posted by emptythought at 6:53 PM on June 18


Unplug the long cable from the pre-amp but leave it in place and change nothing else. Still noisy?

It it is, look at your amp, cable, etc. If it's not, look at your pre and table (and cabling).

Do the same but unplug the table from the pre instead. You can chase faults like this, it gets really fun when you are doing it over an entire theatre or something.
posted by deadwax at 8:38 PM on June 18


The bupbupbup from your wifi is probably the power supply. I can actually hear some of them and its annoying as hell. A new power supply might fix the issue, or move it to another circuit.
posted by fshgrl at 9:50 PM on June 18


Where's your closest AM radio station? I had friends who lived just a couple of miles from the huge Droitwich transmitter in England, and they would quite regularly complain of hearing the ghostly sounds of BBC Radio 4 emanating from their kettle or toaster.

If the AM signal is strong enough, it resonates at all sorts of harmonic frequencies that it shouldn't, and can be 'heard' on various non-radio pieces of electrical equipment. Definitely throw some ferrites on the mains and audio cables (one or two at either end works best in my experience) and see how that goes.
posted by winterhill at 1:24 AM on June 19


Just a piece of anecdata, but my external audio card (digital audio out and shielded RCA cables out) HATES my cellphone being anywhere near it. I don't get the same "bupbupbup," but it's still interference.
posted by kuanes at 5:50 AM on June 19


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