You will not see a 50Hz ripple on a simple voltmeter. You need a oscilloscope that shows the DC output on a CRT screen. In effect you zoom in to a point where you can actually see the 50Hz ripple.

What is oscilloscope? - Definition from WhatIs.com

You can buy a Sky-HD box for next to nothing.

eg

SKY HD BOX AMSTRAD DRX890 500gb Inc Remote And Power Cable | eBay

...
.

You can measure stray voltages with even a farely basic digital test meter although they dont give you all info & I do have Oscilloscopes they are useful to show the voltage if it is at 50Hz. Stray voltages on AV equipment in households today are very common where they are typucally extensively interconnected & especially where aerial distribution &/or multi output lnbs on satellire dishes are included.

As most know on here I install loads of motorised satellite systems, it's the 22kHz diseqc signals to the motor that can serve as a unique but very useful indicator of stray high AV voltages on household AV setups because uniquely those signals can get affected by stray AC voltages even if they are of low power as they usually are. The motor also can act as an earth path. On almost every occasion this happens a fault can be measured as spurious AC usually on the common chassis ground but can be on the 'core' too.

Often stray voltages faults are 1st highlighted by actually receiving a shock when disconnecting / connecting leads & definitely imo should not be solved by attempts to circumvent them but tracked down to their source.
The most common devices to have such faults are old Sky boxes number 1#, old tvs, any older AV gear and some poorly designed / cheap PSUS.

Find the fault and remove it or fix it properly, not just a couple of capacitors but replace whole aging PSUs and these sorts of faults happily track over any interonnecting cables.

Only if it's say a genuine incompatibility issue or a build up of touch voltages & not a fault should a 'fix' be used imo, otherwise you can be masking a potentially serious fault that can cause damage to other newer equipment, or worse, a fire.

I've seen too many of these, it's an issue that now needs addressing, the CAI did offer a bonding solution but I think a device similar to an RCD but designed for this lower power issue and I'm not 100% it should be called an earth loop issue, it's more likely stray voltages.
 
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Other issues around this are SMPSUs producing high frequency energy /AC etc.. hey are amazing how they can be made so much cheaper, smaller & lighter than traditional linear psu' but the main problem with the way they work is the high frequency energy they produce as a byproduct. That when it becomes a problem can't be reliably measured with a basic test meter, doesn't always respect normal electrical separation as it can dance over normal circuitsl design and components, depending 'what' frequency it is and can act as a bridge for larger power.
 
Sorry it's been a long time since I replied. I am the OP of this issue. I decided to make a video please let me know what you think.


BTW forgot to show you, but the issue does persist exactly the same way if I unplug the TV from the mains.
 
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AlexSa, I think the phono isolator on just the TV input will cure this. You won't need to fit them anywhere else.

Worth a punt for ÂŁ6 or so.

Please let me know how you get on.
 
Hi

So this made a significant difference although not fully gone away. I appreciate the step forward.

But something else happened, which was weird... it started happening with pretty much all audio inputs coming into the amp, even inputs not in any way connected to Freesat. Disconnecting the freesat coax kills the noise as per usual. Please note - there is NO bleed in the amps inputs I tested for this.

Here is a A/B comparison via soundcloud:
FreeSat Noise - AB Comparison

So maybe I need to get more of these isolators? :(.
Or the other way is to stop using FreeSat!

Cheers...
 
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I'm glad it's brought an improvement!!

Is this at normal listening levels in terms of the volume control? What happens if you remove the earth connection to the turntable?
 
I'm glad it's brought an improvement!!

Is this at normal listening levels in terms of the volume control? What happens if you remove the earth connection to the turntable?

Recording when is when amp is set to max volume, best way to demo it. It is noticeable at half volume regardless.

I have ruled everything else out by fully unplugging and powering off. The noise just stops when unplugging Freesat cable (as per video). I know the issue is this.

Thx.
 
I would expect some noise from a TV, as their may be a ground loop between it and the dish still. You have removed the main hum loop - which has massively improved things, so is it now audible at normal listening levels? If not, I would call it a win.

It's also worth trying the isolator the other way around. The way they are constructed, this can sometimes help.

If you can still hear it, I guess your only option might be to put a join somewhere convenient so that you can fully disconnect the TV audio when not in use.
 
I would expect some noise from a TV, as their may be a ground loop between it and the dish still. You have removed the main hum loop - which has massively improved things, so is it now audible at normal listening levels? If not, I would call it a win.

It's also worth trying the isolator the other way around. The way they are constructed, this can sometimes help.

If you can still hear it, I guess your only option might be to put a join somewhere convenient so that you can fully disconnect the TV audio when not in use.

Thx, yeah I've tried the isolator in various places.
 
In the end I've just used two of these filters, and gave myself tinnitus in the meantime (seriously). Oh well.e Appreciate everybody's help!
 

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