Humming speakers

December 12, 2019 7:13 AM

I have a very simple setup for my turntable. I got this model. As soon as I connect it to any speaker or headphone there is a really loud 50hz or 60hz humm. I connect the turntable to the output with a symmetrical Jack to 2x RCA Audio Cable like this one. I made the following observations/ tests:

1. The hum persists if I turn off the turntable, but vanishes if I disconnect it from power.
2. There is no hum over the speakers if I connect them to my laptop or old walkman.
3. Turntable and speaker are connected to the same outlet.
4. I tried various cables I had lying around, it was the same with all of them.
5. The hum is stronger on the red RCA.
6. I tried the turntable at different outlets with a portable bluetooth speaker, also humming.
7. All cables are very short and I tested everything at an outlet where no other electrical devices were nearby.

So this is very annoying and I am a bit at a loss what to do next. Any suggestions?

posted by SweetLiesOfBokonon to Technology (18 answers total)

Response by poster: 8. The hum is the same as when I touch the RCA jacks with my fingers.
posted by SweetLiesOfBokonon at 7:14 AM on December 12, 2019

My first instinct is that it sounds like something is not properly grounded... does the power cord for the turntable have a ground pin?
posted by mekily at 7:18 AM on December 12, 2019 [2 favorites]

Response by poster: No, it has two prongs.
posted by SweetLiesOfBokonon at 7:23 AM on December 12, 2019

Response by poster: Though the turntable has a grounding screw. I just connected this to the grounding of my extension with a crocodile clip, but iit makes no difference.
posted by SweetLiesOfBokonon at 7:41 AM on December 12, 2019

The grounding screw needs to be connected to a real ground, separate from your cables -- the cables are likely not a good enough ground in the first place, which is why you have a hum.
posted by AzraelBrown at 7:44 AM on December 12, 2019 [4 favorites]

Agree that this sounds like a grounding issue. Many turntables have or require a ground cable that looks something like this.
posted by gnutron at 8:04 AM on December 12, 2019

Response by poster: I now also think this is the problem but I have no amplifier to connect the ground cable to. If I understadnd it correctly I is no use connecting the turntable ground to a radiator or the ground of my outlet, the goal is to eliminate a potential difference between turntable and speaker. But my speakers have no connection for a ground cable and I have no amplifier or mixer or whatever between turntable and speaker.
posted by SweetLiesOfBokonon at 8:12 AM on December 12, 2019

I think it's totally worth trying to ground to a radiator, if you have one handy, that is a common tip, also recommended on several fora.
posted by SaltySalticid at 8:20 AM on December 12, 2019 [1 favorite]

It is preferable to ground somewhere else than the amplifier -- the reason you have a hum is because the existing ground(s) don't have anywhere to go. This makes sense if you're plugging into some DC-powered speakers or headphones or a laptop, because they're not nicely grounded either, so the "ground" wire just becomes yet another signal source in the circuit, exacerbating the AC hum noise. You might also want to connect the cable "ground" shielding (the outside 'ring' on the RCA jacks) to an external ground too in case they're not properly grounded either (which is likely with cheap converters like that).
posted by AzraelBrown at 8:26 AM on December 12, 2019 [1 favorite]

Response by poster: When grounding to the radiator or the ground of my outlet, it makes no difference. AzraelBrown mentioned I should connect them to a "real ground", I don't know what that means.
posted by SweetLiesOfBokonon at 8:48 AM on December 12, 2019

"real ground" being the radiator or ground in your outlet - something connected to the building's main electrical ground.

I have had similar hums when the cartridge/needle is not seated properly or when wires inside the cartridge have come disconnected.
posted by soundguy99 at 8:53 AM on December 12, 2019 [2 favorites]

If you're sure you're getting a good connection to the radiator (i.e. got a bare metal-to-metal connection with no paint etc), then that would seem to rule out classic ground loop. Can you use a tuning app to check the frequency of the hum? If it's far enough away from AC frequencies or it changes under different configurations, then that would be meaningful, I think.
posted by SaltySalticid at 9:04 AM on December 12, 2019 [1 favorite]

Response by poster: I don't know how to read the output of the App properly, here it is:

The hum seems to be at 100Hz?
posted by SweetLiesOfBokonon at 9:12 AM on December 12, 2019

Turntables need the ground to be connected to the amplifier they are plugged into. Connecting to a radiator or the grounding plug of an outlet will not help. For some reason, North American turntables tend to have a third wire that would be connected to a ground lug on the receiver or amplifier, while European turntables tend to have the ground connected to the outer jacket of one of the RCA cables. Either way works--the European method is easier and eliminates the third wire to the amp. You could try touching the ground wire to the outer metal connector of the RCA plug to see if this provides a ground to the amplifier.
posted by TrialByMedia at 1:27 PM on December 12, 2019 [3 favorites]

Another thought -- since this has a built-in phono preamp, it probably does not need a grounding wire run to the amplifer. This could easily be an unseated cartridge wire. Make sure all 4 wires going into the cartridge are fully plugged in.
posted by TrialByMedia at 1:33 PM on December 12, 2019 [3 favorites]

Sonos have a good no quibble returns policy, you shouldn't have to spend hours futzing with this, just package it up and return it.
posted by Lanark at 4:18 PM on December 12, 2019

Looks like there are a few versions of the Project Essential III, yours is the one with the built in preamp, right? You could have (as Trial By Media & sound guy said) open wires to the cartridge. If there's an open, it will pick up stray hum. The power supply for the turntable could be faulty or the wrong one (IIRC, these Projects use a "wall wart" type) if it's putting out a lot of ripple, it might be able to make the turntable's motor work fine but will wreak havoc with the built in preamp. The preamp itself could be faulty. Just for the record- the comments about "real grounds" and so forth are red herrings- in fact, calling the extra wire on turntables "ground" is kind of a misnomer even if they are labeled as such- it really should be called a shield and should only go to the chassis on the amp, not to the safety ground on an electrical outlet, a pipe, a grounding rod, etc. This is not a big deal in a turntable with a built in preamp, but it's mandatory on a conventional turntable with a cartridge-level output. (Qualifications: electronics technician with over 25 years experience repairing and installing consumer audio equipment.)
posted by Larry David Syndrome at 4:56 PM on December 12, 2019 [5 favorites]

https://en.wikipedia.org/wiki/Ferrite_bead

Pretty sure that is what you need. Old tech needs old solutions.
posted by iStranger at 6:16 AM on December 13, 2019