Balanced Phono Wiring

simon · Post by **simon** » Sat Jan 03, 2015 7:14 pm

I'd like to try running my tonearm wiring balanced from the cartridge to the step ups. If I leave "+" and "-" wires floating then it hums so I think I need a pseudo earth (otherwise they're not balanced I guess).

I can't find anything out there on the net but do I simply add say a couple of 1k resistors in series at the input to the step ups, between "+" and "-", then connect earth to the middle of them?

Are there any particular pros and cons of balanced in this way?

Ali Tait · Post by **Ali Tait** » Sat Jan 03, 2015 10:35 pm

A screen might work?

simon · Post by **simon** » Sat Jan 03, 2015 11:34 pm

Yeah, would do I'm sure. Balanced should negate this though? I guess there's a good reason why most phone wiring isn't balanced per se.

Andrew · Post by **Andrew** » Sun Jan 04, 2015 10:15 am

Most are, I thought, least that's how I do it.

Andrew

Post by **Nick** » Sun Jan 04, 2015 10:35 am

Check its actually flaoting, ie, its not earthed at one side at the cartridge end.

Andrew · Post by **Andrew** » Sun Jan 04, 2015 12:55 pm

Good point, easy enough to change.

simon · Post by **simon** » Sun Jan 04, 2015 4:48 pm

It was definitely floating - I twisted 4 lengths of kynar together and connected to the cart and step ups. It was only when I earthed the "-" wires that the hum became bearable. Which made me think they might not have been properly balanced originally.

IslandPink · Post by **IslandPink** » Sun Jan 04, 2015 4:54 pm

I had exactly the same experience a few years ago . Couldn't get a good result without one side earthed .

simon · Post by **simon** » Sun Jan 04, 2015 9:09 pm

Oh dear, that doesn't bode well. Did you try a pseudo earth Mark?

shane · Post by **shane** » Mon Jan 05, 2015 10:38 am

This may or may not help.

I re-wired my Mission 774 to balanced config a while ago, taking the four signal leads to a 5-way tag strip inside the plinth of the TT2, and the arm earth to the fifth tag. I then used 2-core screened interconnect cable (Navships stuff, PTFE and silver plated copper, a bit like WD's ICT of old) with the screens taken to the fifth tag. I took the interconnects to a 5-pin din plug with the screens to pin 2, and mounted my BBC-type SUTs in an ally box with a 5-pin DIN socket. I connected the signal pins of the DIN socket to the i/p pins on the SUTs, took one of the SUT o/p pins on each channel to an insulated phono socket, and star-earthed the other o/p pin, the case, the SUT bodies and the phono socket bodies back to the earth pin of the DIN socket.

Not a whisper of a hum....

simon · Post by **simon** » Mon Jan 05, 2015 1:11 pm

Thanks Shane, perhaps I just need to screen the wires? Though the hum's okay with the neg wire grounded. Perhaps I should just leave it as it is and concentrate on something more productive!

shane · Post by **shane** » Mon Jan 05, 2015 2:55 pm

If you've go no screening at all, that's probably going to be it. Although balanced operation should in theory wipe out the hum induced, in practice, it often doesn't!

simon · Post by **simon** » Mon Jan 05, 2015 11:11 pm

Yes, and the wires are quite long, maybe a couple of meters which won't help. My thoughts were to go balanced to cancel any hum, but that didn't work! Its interesting that the same wires don't hum if I earth the neg wire though. I might have to try some navships stuff just out of curiosity.

shane · Post by **shane** » Tue Jan 06, 2015 9:27 am

It's good stuff and not hugely expensive. Bit of a bugger to strip though!

http://www.ebay.co.uk/itm/231178888917

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