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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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26th May 2007, 11:53 am | #1 |
Hexode
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Record Decks - to earth or not?
Hi! I have just finished restoring a Marconiphone record player (from approx 1969) as a favour for somebody I know. The old mains lead was a bit scabby, so I have replaced it with a new one (together with new, legal plug!). My question is, would it be good practice to earth the BSR turntable? The single-valve amp chassis is earthed already, but the deck isn't. Also, as the motor body and the deck are separated by rubber mounts, would it be sensible to earth this too? What do others do?
I would normally leave things as they were for myself, but as this is for someone else, I need to be a bit careful. Thanks, Neil. Last edited by Darren-UK; 15th Jul 2011 at 1:48 pm. |
26th May 2007, 1:13 pm | #2 |
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Re: Turntables - to earth or not?
Just out of interest, what is the model number of this player? I only ask because most of the BRC valve players of this era that come to mind used U series valves and the AC/DC technique - with understandably just a two core cable.
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26th May 2007, 2:46 pm | #3 |
Hexode
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Re: Turntables - to earth or not?
Hi Stewart,
It's a Marconi Model 4026. The chassis was definitely earthed - the cable looks like it was the original one (old colours etc.). All it needed to get it going was the usual grease removal / relube of the BSR deck and a spot of switch cleaner on the volume pot. For a single valve set, it gives out quite a decent volume! I have never come across the turntable before, it has a little peg which rises up at the side of the platter to determine record size rather than the more conventional method. |
26th May 2007, 5:24 pm | #4 |
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Re: Turntables - to earth or not?
Indeed - a transformer fed ECL86 circuit! Sorry to have doubted you...but you can't be too careful!
In which case I personally can't see any reason not to earth the motor and turntable metalwork. There is a slight chance of creating a earth loop and getting hum problems given the pick-up ground probably goes to the turntable metalwork as well as the amplifier chassis - but at the gain levels involved I don't think it will be an issue.. Given you mention the amplifier chassis having an earth connection already - does that not earth the turntable via the pickup screen? Links on the centre three tags on the turntable connection tag-strip would suggest so if present. That IS an unusual BSR changer...I've yet to see one in the flesh! It's the UA45 model. I'm trying to think of a good reason for them making such a variation over the standard models - and failing though! |
26th May 2007, 9:24 pm | #5 |
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Re: Turntables - to earth or not?
I would earth the deck, for safety. Should a fault cause the deck to become live you wouldn't be very popular (plus it would fail a PAT test if not earthed).
The motor body doesn't matter as it can't be touched when the record player is being used normally. |
27th May 2007, 12:16 am | #6 |
Octode
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Re: Turntables - to earth or not?
Earthing.....
The worst that can happen if you do is an earth loop...... the worst that can happen if you don't is death. Regards, Trev. Last edited by Darren-UK; 13th Jan 2008 at 10:56 pm. Reason: Made comprehensible. |
27th May 2007, 11:37 am | #7 |
Hexode
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Re: Turntables - to earth or not?
Thanks for that. I always tend to err on the side of safety, but I wondered if earthing could cause any problems. I have just tested it with and without the turntable earth lead fitted and there is no difference to the sound. Was it just penny-pinching which dictated no turntable earthing in the original design I wonder?
Stewart - I didn't realise this was such an unusual deck - I know I have never seen one before though! The deck functions well (as most BSRs do when they have had a bit of lubrication). I have quite a few variations of BSR autochangers from the early Monarchs to the last plasticky things - maybe I should start collecting all the versions and start a mini museum. I know they aren't popular decks in record collectors' circuits or for hifi afficianados, but I have always had a soft spot for them, having always had one or two around when I was growing up - there is something about the sound of them firing up that just takes me back. . . Thanks! Neil. |
27th May 2007, 6:04 pm | #8 |
Octode
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Re: Turntables - to earth or not?
I had an interesting problem with my Rotel RP2500 turntable. This came with two core mains cable which I thought was unusual. At the time I used it with my Technics SU-Z150 amplifier, which is also two cored although did have a provision for Earthing the turntable.
The results with this combination resulted in a background buzz with a "brush tingle" feel on the turntable's metal parts, clearly akin to leaving the Earth disconnected in any 3-cored appliance when working normally. I replaced the turntable's flex with a 3-core one which solved both problems. The reasons for this are interesting: In 1975 when the turntable was made non Earthed amplifiers were just about unheard of. The turntable was dependent on the Earth connection at the amplifier, which was proven on trying a Pioneer 3-cored amplifier with the turntable before fitting the 3-core flex to the latter! The turntable is now connected to my Leak Stereo 30 with no need to fit the turntable's original Earth lead to it, both now being 3-cored of course. Thec Technics is now used as a main amplifier. Brian R |
30th May 2007, 11:21 am | #9 |
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Re: Turntables - to earth or not?
Hi
The motors are double insulated with no need to earth and if the chassis is earthed so will the deck be through the screen of the input lead so should be ok. Regards Peter. |
10th Jun 2007, 8:37 pm | #10 | |
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Re: Turntables - to earth or not?
Quote:
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11th Jun 2007, 12:37 am | #11 | |
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Re: Turntables - to earth or not?
Quote:
Re. hum loops. Easy to prevent. Thoroughly ground the autochangers' metalwork to the mains earth, but make sure the "signal" earth (ie cartridge "cold" connection and cable screen) is not connected to any metalwork. This should be grounded only via the amplifier's input. Pete |
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11th Jun 2007, 8:43 am | #12 |
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Re: Turntables - to earth or not?
This is where I feel that the 'rules' that relate to PAT testing needs to be followed.. If the turntable has exposed metalwork that can be touched. And what it is connected to (be it control circuitry or motor) isn't double insulated or isolated via a transformer. Then it should be earthed.
As for Hum / Earth loops. Most stand alone turntables have a seperate earth lead that connects to a terminal on the amplifier.. The point of this is to create a star earth system, which avoids hum loops. Star earthing is standard practice in sound studios. Once you have got your head around what earth loops are about. You are then on the way to getting it right everytime. Regardless of what the equipment is.. There is lots of technical information available about this if you do a quick search. If in doubt ... Earth it. Your life is valuable. Trish |
17th Jun 2007, 9:01 pm | #13 |
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Re: Turntables - to earth or not?
Trish is right of course. I suppose the bone of contention is that alot of our beloved old stuff isn't made to modern standards...so do we make it conform, or leave it? Since safety is the main issure regarding 'modern' standards, then I reckon it's best to err on the side of safety. I shan't go on since this approach has been covered elsewhere....
However, even 60 year-old stuff was made such that you wouldn't get a shock (no matter how small!) if it was all working correctly...any subsequent problems are all about deterioration of insulation rather than downright design faults. So we must now address these deterioration issues (and potential for deterioration) in the 21st century! If you are worried about introducing hum-loops on turntables (a real problem with adding extra safety earths), then why not add an audio isolating transformer between pick-up and pre amp? Maplin, CPC and goodness-who-else do these for a couple of quid or so and are about half-an-inch square so will fit anywhere. I've used several of these when renovating vintage organs where the owner wants to interface them to modern mixing desks for studio use. |