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Safe earthing of Quad II amps connected to a passive preamp

ampedup

ampedup

Lost in audio
I did some research on this and discovered this thread from back in 2015:
https://pinkfishmedia.net/forum/threads/quad-11-earthing-issues.174877/
I'm still not clear how to do it.
My amps have had the Jones plug replaced by an in-chassis rca socket.
They are powered by the original two-pin bulgin plug, to two-prong USA type mains plugs, into an earthed heavy duty Tripp-lite multi-outlet.
The passive pre has no earth connection.
I'm using well-shielded interconnect between them.

How exactly do I provide earthing for my two amps?
Thanks.
 
I’d expect the Quad IIs, like vintage Leaks, for that matter the 303 to have the amps chassis as ground. If so then taking new ground wires to appropriate case bolts (e.g. attach an eyelet to one of the bolts that hold the bottom panel on or similar and take that to the earth pin in the mains plug) would do all you need. Not especially elegant, but that would certainly earth it. You could do it fairly neatly with a three-core mains lead to the Bulgin connector with the earth exiting just before and going to a suitable eyelet to be bolted to the case. I’d get someone more knowledgeable than me to second-guess this though, but I can’t see a direct case earth as anything but safe, and it could certainly be done without damaging the amp in any way.

PS I didn’t like the wording of my post on the earlier thread so I’ve deleted. Bottom line is I would not be happy with any scenario where a vintage valve amp with a metal chassis wasn’t directly earthed.
 
Thanks Tony, I imagined that to be a possible way to go. But I profess no knowledge of things like earth loops etc, so I welcome affirmations of your post from others too, for my peace of mind
 
I’d only worry about earth loops if and when they appear, and then deal with them up-stream of the Quads. I’d personally keep the vintage valve amp earthed in all scenarios. That’s where the high voltages are!

PS There is a fashion in audiophile circles to bung 13 Amp fuses in mains plugs as a matter of course. Check your Quads have 3A fuses as IIRC that is all Bulgin connectors are rated for. Same goes for two core mains wire IIRC too. My Leaks thankfully have three pin connectors so are fully earthed, fuses are all correct too. Always worth checking these things. I never power up any second hand piece of audio kit without checking everything.
 
Tony L said:
I’d personally keep the vintage valve amp earthed in all scenarios. That’s where the high voltages are!
Click to expand...
OK, will do. I can maybe use the screw to the left of the bulgin socket, scraping some paint from underneath.
 
ampedup said:
OK, will do. I can maybe use the screw to the left of the bulgin socket, scraping some paint from underneath.
Click to expand...

That looks perfect. You won’t need to worry about the paint, it will find earth from the bolt thread. Just do it nice and tight and check everything with a multimeter for continuity. I’d crimp or solder (or both!) a round eyelet (so it can’t come loose) to the earth wire, heat-shrink it so there is no way it could swivel and find its way under the Bulgin and bolt it down nice and tight. I can’t see that not being a safe earth, but I’d still wait for a grown up, e.g. @martin clark, @Robert or @snowman_al to confirm.
 
IMG-0144.jpg

This worked out well and is relatively easy to do. I used a standard 10A computer cord, cut the female end off and wired the bulgin plug on to it, leaving the earth wire with some length to play with. I tinned all wire ends first. This is necessary to get a good contact under the screws inside the bulgin plug. I found a small crimpable spade connector for 18-22 AWG wire, and I had to get inside the amp chassis to loosen the left hand screw of the bulgin socket, since it has a nut on the inside. The spade connector fit perfectly and is very tight under the screw head. Tested for continuity all through the system. I feel down to earth now. thanks Tony.
 
I stress my electrical knowledge is near zero but that's very similar to what I've done on my Quad ll's. My earth goes under the chassis to the screw that holds bottom plate.
Have a feeling though I read somewhere (could have been the keith snook pages) that the earth wire should really go to the bare chassis and not just the outer plating ?
 
bill spears said:
I stress my electrical knowledge is near zero but that's very similar to what I've done on my Quad ll's. My earth goes under the chassis to the screw that holds bottom plate.
Have a feeling though I read somewhere (could have been the keith snook pages) that the earth wire should really go to the bare chassis and not just the outer plating ?
Click to expand...

Yes, ideally you should scrape the paint off and make sure the earth connection is to bare metal.
 
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