Mains interference - culprit found (see later post)

[flash]

Going for this....

So I think I know I need to put an unearthed (at one end) phono pair betwen my tuner and amp. Before I apply this magic healing balm...

1) If the earth connection (apparently) serves no function in normal use then why is it there?
2) Is this a procedure that anyone who can change a plug can do by following a few instructions, or does it require a specialist?
3) I'm happy with my Van den Hul i/cs generally, though I don't do much high fidelity listening using the tuner; but out of interest, is disconnecting the earth going to change the performance/dynamics in any way besides getting rid of the hum?
4) If you don't need to be a geek to give a phono cable "the snip", can anyone point me to instructions on how to do this?

I suspect the end result is probably going to be getting someone else to sort this but I'd be interested in further info on the above.

Thanks,

Nigel

 

[Tenson]

The earth does serve a purpose. When interference hits the cable it is conducted by the shielding down into the earth and away from your audio signal. By disconnecting one end of it you still leave somewhere for the interference to go. Normally both ends are connected to ensure that both units see the same potential difference for the hot line. However both your units are clearly using the same earth so it doesn't necessarily need it.

Here is yet more of my brilliant art work lol! The inside of your phono plug should look like this. The shielding of the cable should be connected to the earth 'clamp' of the RCA. The hot line will be connected to the centre pin on the RCA. You need to disconnect the earth. This might be a bit tricky to do as they are normally soldered on. You could use the soldering iron to heat it up and try to wiggle it free, or you can simply snip the actual RCA where that long arm part is. You would not be able to put it back how it was if you did this though.

 

[flash]

Experiment 1 - AV ok, tuner not...

Interconnects are Van den hul D102 III Hybrids. I won't try to draw the components at each end because I can't compete with Tenson's skills but the outer (earth) consists of four parts:

1) threaded outer connector which normally connects to source/amp. If unscrewed this is removeable from the cable assembly
2) threaded outer connector which screws into this. if unscrewed this slips down the sheath of the cable freely
3) inner clamp which goes right round the cable (not just a single bridge a la Tenson cartoon)
4) inner sleeve which butts against this and lives predominantly beneath (1)

I unscrewed (1) and (2) at the source end of both cables, removed (1) and let (2) slip down the cable.

I put the inner connectors into the source (tuner) and the unmodified ends into the amp. Thus there was no connection from the tuner to the cable sheath (earth).

The AV mains hum has gone.

The problem is the tuner now! Whereas the amp had a low hum the tuner had a higher pitched noise which was never really an issue as we don't listen to the tuner at such volumes that is noticable. With the modification however, it is as if the mains hum has been transferred to the tuner and overlayed on the higher pitched noise. In real life use this is less of an issue than the AV hum but it seems less than satisfactory.

Advice so far has really helped in narrowing down the problem. If the above description is sufficient to allow anyone to proffer further advice then it would really be appreciated.

Until I understand what is happening, I don't want to splash out on new unearthed cables or other solutions only to find that, perhaps because I have inadequately described what is happening, the problem remains.

Thanks in anticipation.

Nigel

 

[Tenson]

I found the description a little hard to follow, but if we assume you have disconnected the earth of the cable at one end then I'm a little unsure of what the issue is now.

You might like to try the cable the other way around so that the earth is disconnected at the other end as it were. It would only change what path interference in the cable takes to dissipate but you never know what it might do!

The other thing is, does the tuner have an earth tag on the back? You know the little screw things you can connect to a good earth. If it does then you could try connecting that via a wire to a radiator pipe or something.

The problem only lies with the tuner now? Everything else works fine?

I'm sure someone will come up with a suggestion!

 

[flash]

tuner earth

Thanks Tenson, I'll check out the "little screw" option and see if I can earth separately. I'll also try cable the other way around tonight.

I might even see if I can rustle up a diagram from somewhere as I knew the words might be a bit hard to follow...

 

[flash]

Picture attached (I think)

Attached is pic of VDH connector (I hope, never uploaded pics before).

You should be able to see (1) the outer connector with the VDH label, (2) the outer knurled connector which screws into this, (3) the end of the inner sleeve. And of course the central connector. The bit you can't see is the earth "clamp".

Not sure if this helps!

In stripped down mode as tested, (1) is removed, (2) floats down the cable, and (3) is also removed. The clamp remains in place but the tuner earth is not connected to it.