Weird intermittent hum from phono stage. Ideas?

This morning I turned on my system to be greeted with a nasty mains hum. I was playing records last night and it was fine.

It only presented through the phono output so I started messing about with the phono chain.

I was bloody worried because I’ve just bought a new to me cart and it would be sods law that having bought it from a mate, it would go wrong. So I disconnected the leads from the arm and that made no difference. Shit, phono stage (Pro-ject Phono Box SEII) has gone was my next thought. I picked it up and as I did the hum disappeared. So I moved it around a bit and the hum came and went. I checked that the cables weren’t dodgy and that no mains cables were parallel to the interconnects.I unplugged the 401, hum gone. Plugged it back in, hum back.
I remembered a diagram showing how EM fields are sort of a fat, 3d, figure of 8 vase shape and that would account for the hum coming and going as I moved the stage around.

I swapped out the pro-ject for my Angle Audio and got the same result (plus a lovely pulsing throb from the WiFi, which I know the Angle is sensitive to).

Changed everything back, tidied the cables & the the hum was still there.

At this point I was about to lose it and do something that would end up being an insurance claim to be blamed on the dog/kids/both.

So I turned everything off and went to the beach with Claire and the dog.

Got back about an hour ago, turned everything back on…

No hum. Nothing until you turn the volume knob to about 3 o’clock, which is stupidly loud if music is playing.

Sooooo, in the words of Marvin Gaye, what’s going on? @Agrail @Valvebloke?

Cables

Don’t think so Adam, the cables are exactly as they were this morning when the hum was there, now the hum has gone.

I’m thinking something like a 40yrs old capacitor or something in the Garrard is on its way out?

The Spark Suppressor on the Garrard will simply keep the motor turning with the unit off (Still on at the wall) if faulty.
Take a single core piece of cable and touch the tonearm base with one end and touch the other end to the top (or underside of the Garrard chassis - Does this knock the hum out?

Are the cart tags touching or faulty?

It is odd that the hum comes and goes, it rather suggests a wiring failing. If the phono was too near a field it would be constant. if the deck was playing up it would likely be constant. An internal arm wire issue / phono cable / grounding point may cause intermittent hum

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Cheers Matt, I’ll try that in the next day or two.

Cart tags are fine, I’m pretty sure they are any way. But I have just changed the cart so it’s definitely something to look at.

I’ll have to check the arm wiring (hope it’s not that, because it’s a Tabriz ZI and the cable is relatively expensive). My only multimeter is an automotive one so probably not suitable, but I’ll dig it out and see if it’s able to check the continuity.

But as I said, with the arm cable disconnected from the phono stage the hum was still present, being picked up by both of my stages. It was definitely coming from the turntable electrics because when I unplugged it from the mains it went away.

A dry joint in a cable is a great candidate for an intermittent hum problem. Also a nightmare to find.

Is the hum on/off, or does it very in intensity with how you move the items around?

Are you sure it’s not just the usual rumble? :grin:

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It varied as I moved the stage around, but an EM field isn’t a perfect sphere so you would expect that.

Did it vary as you touched anything?

Tend to favour this given it’s intermittent and responds to movement - it’s not necessarily cable, but people do abuse the poor things (and their sockets), especially by twisting them to unplug, and pulling them out by the cable not the plug. Certainly worth trying some spares in the first instance.

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No, except when I touched the earth post on the stages, then it decreased very slightly.

If it’s a faulty cable, then it has to be in the stage -> amp cable, so if it comes back I’ll try swapping that out.

Could also be the sockets rather than the cables

On both stages? Could be I suppose, but I doubt it.

Also, forgot to mention, it came from both channels.

That would be your dipole field sir, seen here rotating, which they often don’t

Was the 401’s motor running when you had the hum ? If not then the field’s unlikely to be primarily magnetic. My first thought might be a loose ground connection somewhere in the 401’s wiring (electric fields can be spatially varying too). When you say ‘I unplugged the 401’ was that unplugged from the Phono Box or unplugged from the mains supply ?

EDIT I started to write this about 2 hours ago. Then suddenly there was competition from dinner (er, no contest) and in the meantime I now see you’ve had loads of other replies, some of which also suggested iffy wiring.

VB

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Best diagram on here for a while. Kudos.

Why are there sperms? Nobody told me electrickery had sperms. :open_mouth:

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Courtesy of these people http://earthweb.ess.washington.edu/space-propulsion/plasmamagnet.php. Heaven knows why they’ve put tails on their electrons.

VB

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It hummed when the platter was both turning and stopped. I need to check Matts observation about a faulty spark suppressor to see if the motor stops when I turn the switch to off.

From the mains.

The Spark suppressor is probably a separate issue - Some tonearms need to be earthed to the ground point of the phono and another wire to the chassis (Hence the touch a wire to the base of the arm and the chassis to see what happens) This would in most cases not be an intermittent fault but rather a constant.

As the noted variable is changing carts could you swap back to see if the issue persists?

I could Matt, now I know how the Transfiguration sits in the headshell so it wouldn’t be a total ball-ache to re-align, but it still hummed when the tonearm cable was disconnected from the phono stage, so surely that takes the cartridge & tonearm wiring out of the equation?

It seemed to me like both phono stages (or possibly the interconnect from the stage to the amp) were picking up something “radiated” from the turntable rather than sent down the tonearm cable to the stage.

I iz confuze…