Bonky
Rank: Trio
Posts: 156 
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Post by Bonky on Mar 30, 2018 18:24:49 GMT
A Schiit Saga driving a Quad 306 = no mains hum.
Quad replaced with a valve amp = mains hum
If earth lead from the Saga is removed = no mains hum (Saga is presumably still earthed via interconnect's screens from the amp) (?)
However, many folk have advised replacing the Saga earth.
I've looked at other possibilities: mains lead away from the inputs; screened mains cables etc.
Should I replace the earth? If so, what can I do re the hum?
Thanks.
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Deleted
Deleted Member
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Post by Deleted on Mar 30, 2018 18:54:24 GMT
As it's an earth loop causing the hum, I'd see no advantage in replacing the earth. It must already be earthed when connected.
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Post by DaveC on Mar 31, 2018 7:45:17 GMT
What valve amplifier are you using ? And if you just have the pre-power interconnect, no inputs plugged in at all, does it hum ?
Dave
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Post by dsjr on Mar 31, 2018 11:25:46 GMT
The Schiit Mani phono stage can have hum issues, although this may well be unrelated!
I discovered lately that not all amps like a passive volume control feeding them and in my case, increasing hum with increasing level when fed from a 10k log pot. Using the once recommended active preamp cured this and no hum at deafening volume levels.
Quad used to have the preamp earthed and the power amp was 'earthed' via the signal leads. having the power amp connected to the mains directly via a three core mains cable along with the preamp's three core lead and there was always a hum loop, but this was more at all volume levels I recall.
From an amateur distance, if the valve amp has a mains earth, then leave that intact. Hopefully the Schiit will be 'earthed' via the signal leads. You could check with Schiit on the safety of this first though? the US still uses twin core mains mostly doesn't it? (S'cuse my ignorance here). Unlike Dave C, I'm not able to properly and confidently discuss floating or semi-floating earthing arrangements. In my book, if it works it works, so if removing an 'earth' from the Schiit works with no hum, then fair enough...
P.S. I've just looked the saga up. In the pics on the European site, it appears the IEC mains inlet is two-pin. On the back of the socket though (board view) it looks as if it's three pin.. As I don't know the earthing arrangements and can't check with a meter, I can't say more, so please regrd my comments above as jottings and thoughts-out-loud  |
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Bonky
Rank: Trio
Posts: 156
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Post by Bonky on Apr 2, 2018 8:48:31 GMT
What valve amplifier are you using ? And if you just have the pre-power interconnect, no inputs plugged in at all, does it hum ? Dave The Schiit Saga preamp feeds a recently made (and very good) WD KEL84 valve amp. No hum now that the Schiit earth lead is disconnected. No hum if all input leads are disconnected. Thanks. |
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Bonky
Rank: Trio
Posts: 156
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Post by Bonky on Apr 2, 2018 8:51:20 GMT
Thanks; understood.
On the WD forum the Uber-Guru (John Caswell) has given it (disconnecting the pre-amp earth ) his blessing, so I'm sticking with that at present.
Thanks again.
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Post by DaveC on Apr 2, 2018 9:35:34 GMT
Thanks; understood. On the WD forum the Uber-Guru (John Caswell) has given it (disconnecting the pre-amp earth ) his blessing, so I'm sticking with that at present. Thanks again. OK, but didn't the pre-amp have only two pins of the IEC connected, so no earth anyway? Or are we talking about another earth ? Whatever I would have both units PAT tested as the WD is probably not CE certified. Regards Dave |
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Bonky
Rank: Trio
Posts: 156
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Post by Bonky on Apr 2, 2018 10:13:19 GMT
Dave, the original lead is 3-pin and yes, the earth is connected from the mains plug to the IEC plug (just tested with my DMM).
After I built the amp I had it tested by Matthew Snell (the very helpful owner of World Designs); all the voltages seemed ok and although I had made a mistake with the wiring of the feedback wire, he deemed it safe to operate.
Thanks,
Richard
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Post by DaveC on Apr 2, 2018 10:33:41 GMT
Dave, the original lead is 3-pin and yes, the earth is connected from the mains plug to the IEC plug (just tested with my DMM). After I built the amp I had it tested by Matthew Snell (the very helpful owner of World Designs); all the voltages seemed ok and although I had made a mistake with the wiring of the feedback wire, he deemed it safe to operate. Thanks, Richard Which original lead, and is the earth connected internally, is the equipment socket 2 or 3 pin ? Did Matthew do a PAT test ? Dave |
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Bonky
Rank: Trio
Posts: 156
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Post by Bonky on Apr 2, 2018 10:43:50 GMT
The original (3-pin) lead that came with the pre-amp. It's near-impossible to disconnect the earth on this as everything is sealed, so I used the MRCU screened lead I was already using anyway with the pre-amp and just disconnected the earth at the IEC end - but kept the screening earthed at the mains end.
Matthew didn't mention a PAT test.
Thanks again for your interest.
BW
Richard.
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Post by DaveC on Apr 2, 2018 11:06:32 GMT
OK, that doesn't answer my questions and you do need a PAT test. But I'll leave it here now.
Dave
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