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Thorens TD160S MkV - Speakers are picking up radio signals!

oztayls

oztayls

Member
Hi all, I'm looking for some advice from Thorens owners.

I've just bought a nice TD160S MkV on eBay and fortunately it has arrived in one piece. I've not owned a Thorens before. It has a Grace 707 tonearm and the RCA leads are also Grace. After having spent a few hours putting some things right, for eg. the platter wasn't level and not bouncing correctly. There were a few other minor issues as well, but I've managed to sort them out and get it set up. I plugged it in to my old Yamaha CA 610 amp and turned it on. First off, there is a bit of hum through both speakers, but not only that, I can hear a radio broadcast!

I noticed the tt did not have an earth connection and when I had the back cover off, I noticed that it is earthed through the power point's earth pin. Could this be causing some kind of earth loop, or is the problem the old RCA leads that may not be as well shielded as they should be? The cable doesn't look to be in bad condition though.

Would it help if I installed an earth wire to the metal chassis and connect that to the ground on the amp? Is it OK to leave the earth pin ground in place or should I disconnect it?

Any help would be appreciated.
 
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No Thorens TD-16X has a stock ground scheme that involves the mains input - ever. If that's what you have, it's been tweaked. It's not necessarily bad, but you need to verify it had been done correctly. The tonearm grounding connects to the chassis, the sub-chassis connects to the chassis as well, and chassis goes to the ground prong on the mains input. If just one of these connections is missing, or more than one is connected to ground - it hums. You should also verify nothing is still grounded with the stock grounding scheme, to the right channel's shield. The two alternative grounding schemes should never be mixed. It's either the first, or the second, but never parts of each combined b/c that's what causes ground loops.

All of this got nothing to do with radio interference. It could be related to bad RCA cable shielding or even to exposed tonearm wires, but it may also be related (and more likely) to your amplification.

This is the stock right channel RCA shield grounding scheme - not connected to mains ground

TvTrM7J.jpg


This is the alternate grounding scheme - including mains ground, cancelling RCA shield

lZEGZ8a.png
 
tnsilver said:
No Thorens TD-16X has a stock ground scheme that involves the mains input - ever.
Click to expand...

Unfortunately that's besides the point. The MkV doesn't run on mains voltage, it uses the 16 volt motor and a wall wart.

@oztayls - What cartridge are you using? And when you say your old amp, do you mean you haven't been using it recently? As tnsilver said, it could be a problem with the amp. Also, please update the location in your profile. It shouldn't matter for a low voltage model but the mains-driven ones are of course different depending on the intended region.
 
I found the proper schematic for the MkV on a German forum http://new-hifi-classic.de/Gallery/albums/userpics/TD 160 Mk 5 schaltplan 2.jpg

Wire colors are marked in both German and English but the AC input is marked 220 V, so it may be specific to units sold in Europe.

Your shield is in the bottom left corner, the wires labeled nf / CL. No idea what wire color that is supposed to be, I can't make sense of it in German or in English! I'm not very good at reading schematics, unfortunately. It looks to me like the shield should be connected both to the housing (the dashed rectangle) and to a ground point on the outside (the open circle), presumably for a wire to the amp. I have no idea why there are two parallel lines labeled nf, though.
 
tnsilver said:
The tonearm grounding connects to the chassis, the sub-chassis connects to the chassis as well, and chassis goes to the ground prong on the mains input.
Click to expand...
If minor hum and RFI are present, the arm connection may be deficient (flaky).
Remember a good arm ground connection is reliant on connection to a moving object.
 
bang4buck said:
Unfortunately that's besides the point. The MkV doesn't run on mains voltage, it uses the 16 volt motor and a wall wart.

@oztayls - What cartridge are you using? And when you say your old amp, do you mean you haven't been using it recently? As tnsilver said, it could be a problem with the amp. Also, please update the location in your profile. It shouldn't matter for a low voltage model but the mains-driven ones are of course different depending on the intended region.
Click to expand...
Cartridge is an Ortofon OM20E. Amp is a Yamaha CA610 which I've been using with a Rega Planar 2 (2017 model) Yamaha YP211 and also a Dual 740. No hum from those tts. I've also plugged it into a newish Yamaha A-S501 and the hum is even worse! I'm in Australia, mains is 240V/50Hz.
 
Mmm, thanks guys. I'll now have check the tonearm and cartridge wiring it seems. The earth/ground looks OK to me. Here is a pic I took earlier this morning.
 

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Don't look at it - test it with a meter (continuity) and make sure the black wire from the tonearm to sub-chassis is not connected to one of the RCA shields. I guess it's a DIN plug at the TA? It could be faulty. That same black wire which I assume is TA ground, should be hooked to the main chassis and looks too thick anyway. So does the gray wire that's suppose to connect the sub-chassis to the main chassis. Too thick! The soldering on the grounding point could use some testing too - I can't tell it's condition from the picture. The whole tonearm wiring from the pillar looks like a potential antenna to me and was never suppose to be connected this way. These are not suitable tonearm wires for a suspended table and if not an antenna on their own, definitely look as if they interfere with the sub-chassis suspension.

Look... "hum" is mains frequency disturbance (50Hz in AUS) and is most often caused by grounding related issues. Radio Frequency Interference is a high pitched "buzz" and not related to grounding.
in your case, hearing radio broadcast on the speakers while listening to a TT means something in your TT/pre/amp chain had turned to an antenna. Looking at this TT wiring - there's not too much guess work involved. I think you suffer symptoms of both hum and buzz.
 
I can't really make it out but that does look like a non-standard power arrangement. I would expect a socket and plug from the wall adapter, much like a laptop, but the power cable seems to continue. Is that mains voltage, after all? If so, it conforms to the second scheme tnsilver posted above (arm, subchassis and top plate all tied to mains ground).

I would try lifting the arm ground wire from the subchassis and connecting it to the amp instead.

The radio signal is probably a separate issue.

ETA: I see we posted at the same time. Good point to test for continuity.
 
Guys, radio breakthrough was/is a common issue with phono front ends. You can kill it with a RC filter and/or LC filter. It has nothing to do with his earthing. He is near a reasonably powerful AM station.

RFI is a different issue altogether.

Where in NSW are you? I'll tell you the station you are hearing. :)

It can also occur with amplifier speaker leads acting as a nice antenna with basic detector duty being performed in the NFB loop and bingo- you have a free AM tuner (only tuned to one station- the most powerful local one).
 
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By the way, the ground wires don't look unusually thick to me, but the gray one probably touches the arm cable when the unit is right side up. That will transmit vibrations right up to the arm and cartridge, bypassing the suspension.
 
He doesn't have it with different TT's - just this one so it's not speaker cables. If it is indeed a "hum" as the OP calls it, it's ground related and is not inconceivable to occur in conjunction with parts of the TT wiring picking up radio signals.

Where does this go on the TA? If this has any continuity with any RCA lead - it's a ground loop.

YSURkdF.jpg
 
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OK, looks like I need to relocate those "problem" wires anyway, so thanks for pointing out this issue. I've just taken a piece of copper electrical wire, touched the sub chassis on one end and the ground on the amp, and it all went completely silent. No hum, no buzz, no radio reception! Is it really as simple as me just making this new earth/ground connection wire for connection to the amp? I mean, if this works, could I just leave as is and make a sub chassis to amp earth wire?
 
Haha. Yes Tom, it's a DIN at the TA. It also doesn't feel too secure so I'll check that TA ground as you say and tape the DIN firmly so it doesn't fall out. :)

Many thanks for the contributions guys, I've learned a lot! :)
 
On the plus side, the previous owner did take the time to adapt the stock Thorens armlift to the Grace. How's that working?

While you're at it, it's a good time to set this on a glass tabletop without the bottom and check what the various cables are doing. That arm cable is unsupported all the way to where it leaves the plinth. Probably touches the bottom, again shorting the suspension.
 
bang4buck said:
On the plus side, the previous owner did take the time to adapt the stock Thorens armlift to the Grace. How's that working?

While you're at it, it's a good time to set this on a glass tabletop without the bottom and check what the various cables are doing. That arm cable is unsupported all the way to where it leaves the plinth. Probably touches the bottom, again shorting the suspension.
Click to expand...
Yes, that arm cable sure was sloppy. All fixed now and sounding fantastic, as it should.
 
bang4buck said:
On the plus side, the previous owner did take the time to adapt the stock Thorens armlift to the Grace. How's that working?
Click to expand...
The stock Thorens armlift works well and is quite an elegant solution. I have the Grace armlift mechanism in the event I ever sell the arm which is great. The only possible issue might be playing a warped record as there isn't much leeway in the movement of the lift. The stylus only clears the record by 5mm (<1/4") when in the lifted position. But then I don't have any warped records so it's not an issue for me.

PS. I once bought a nice turntable that was "faulty" and described as not tracking records properly, and skipping. There was nothing wrong with it, it was just a badly adjusted armlift. :)
 
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