Thorens TD150 hum following re-wire. - UK Vintage Radio Repair and Restoration Discussion Forum

qualityten · 31st May 2009, 9:00 pm

I obtained an dusty original TD150 Mk1 today which needed to have its rusty RCA sockets replaced. I soldered a new cable with sockets directly to the tags, but can't quite silence a soft hum.

I've checked my soldering, including the original grounding, as well as other things like the contacts between the cartridge and tags. I also tried an earth link from the mains plug to the earth screw of the deck.

The hum is not loud at low volume, but is louder than my TD125. Might it be deteriorated wiring within the arm? Any other suggestions would be appreciated.

David

Nickthedentist · 1st Jun 2009, 12:51 am

Hi David,

As supplied, the chassis of the deck was earthed via the screen of the RH output cable. You should be able to spot a link connecting the tag that's connected to chassis, to ONE of the screens.

Check that only one screen is connected to this earth, or you'll get a hum loop.

Could you post a picture of the tagstrip where you've soldered the new lead?

Nick.

qualityten · 1st Jun 2009, 8:27 am

Hi Nick,
The deck is unmolested (or was when I got it!), and the earthing arrangement was as you describe.

Noting a suggestion on another site (re. a TD125: to separate the ground from the signal cable completely and have a dedicated ground wire to the chassis, with tonearm ground connected to this), I tried disconnecting the link. But this made matters worse, so I replaced it.

I'll post a pic of the underside this evening.

David

Nickthedentist · 1st Jun 2009, 1:09 pm

Hi David,

A few other things to check:

(1) Is the amp near the turntable? As you no doubt know, you will get hum pickup by magnetic cartridges from the amp's power transformer. Try moving it further away or rotating the deck.

(2) Presumably the deck has the original 2-core mains lead with no earth. If someone's fitted a "safer" 3-core one, hum loops can result.

(3) Does your cartridge have a little lug under one of the signal ground pin, linking this pin to the cartridge body? Sometimes, these can introduce a hum loop, as the arm is then being grounded in more than one place.

(4) Have you tried removing and replacing the headshell a few times, to clear any bad connections there? (assuming yours is fitted with a Thorens arm).

(5) Does the level of hum vary if you touch the arm, or if you move the arm towards the centre spindle?

Nick.

qualityten · 1st Jun 2009, 9:34 pm

Thanks for latest suggestions Nick. Will check these. As promised, here is a pic of the tag connections and one of the front of the deck, just for interest.

David

Nickthedentist · 1st Jun 2009, 9:46 pm

That looks fine as far as I can tell. Where do the grey and second black wires connected to the earth terminal go?

I do like the Goodmans presentation. Very 1970s styling, and much more robust than the Thorens plinth and dustcover. The latter always seems to crack.

They also came badged as Leak, Tandberg and many other well-known brands.

Nick.

qualityten · 1st Jun 2009, 10:02 pm

Have made the checks you suggested. None of those tweaks affect it. But, to be honest, it is pretty minimal at normal listening volume, before a record is put on.

What does increase the hum is handling the cable to the RCAs. I just took a cheapish interconnect. Perhaps it is not adequately screened?

David

Nickthedentist · 1st Jun 2009, 10:35 pm

Quote:

Originally Posted by qualityten

What does increase the hum is handling the cable to the RCAs.

That's very odd, I've never come across this.

Have you got an alternative amp you could try it with?

It really should be silent. Mine certainly is.

Nick.

AlanBeckett · 1st Jun 2009, 10:51 pm

Nick,
[There's a lot of TD150s about at the moment!]
I don't remember mine, into a Leak 2000, producing any hum at all. Indeed, the first sound you heard was the usual hiss as you lowered the head on to the record. I think your idea of another amp would be a good test.
Alan

qualityten · 2nd Jun 2009, 8:49 pm

Hi Nick and Alan

The moment Alan said that it should be silent, I realised it must be a poor connection somewhere. I checked it with another solid state amp and it turned out to be the replacement RCA cable.

I've just put a replacement in and it's dead silent. Result! Now I just need to source the missing outer platter, probably from the usual dodgy sources.

Many thanks to you both, and apologies to the moderator for giving him some work.

David

Nickthedentist · 2nd Jun 2009, 8:53 pm

Well done!

AlanBeckett · 2nd Jun 2009, 9:11 pm

Splendid!

31st May 2009, 9:00 pm	#1
qualityten Octode Join Date: Feb 2009 Location: Wallasey, UK. Posts: 1,314	Thorens TD150 hum following re-wire. I obtained an dusty original TD150 Mk1 today which needed to have its rusty RCA sockets replaced. I soldered a new cable with sockets directly to the tags, but can't quite silence a soft hum. I've checked my soldering, including the original grounding, as well as other things like the contacts between the cartridge and tags. I also tried an earth link from the mains plug to the earth screw of the deck. The hum is not loud at low volume, but is louder than my TD125. Might it be deteriorated wiring within the arm? Any other suggestions would be appreciated. David

1st Jun 2009, 12:51 am	#2
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,865	Re: Thorens TD150 hum following re-wire. Hi David, As supplied, the chassis of the deck was earthed via the screen of the RH output cable. You should be able to spot a link connecting the tag that's connected to chassis, to ONE of the screens. Check that only one screen is connected to this earth, or you'll get a hum loop. Could you post a picture of the tagstrip where you've soldered the new lead? Nick.

1st Jun 2009, 8:27 am	#3
qualityten Octode Join Date: Feb 2009 Location: Wallasey, UK. Posts: 1,314	Re: Thorens TD150 hum following re-wire. Hi Nick, The deck is unmolested (or was when I got it!), and the earthing arrangement was as you describe. Noting a suggestion on another site (re. a TD125: to separate the ground from the signal cable completely and have a dedicated ground wire to the chassis, with tonearm ground connected to this), I tried disconnecting the link. But this made matters worse, so I replaced it. I'll post a pic of the underside this evening. David

1st Jun 2009, 1:09 pm	#4
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,865	Re: Thorens TD150 hum following re-wire. Hi David, A few other things to check: (1) Is the amp near the turntable? As you no doubt know, you will get hum pickup by magnetic cartridges from the amp's power transformer. Try moving it further away or rotating the deck. (2) Presumably the deck has the original 2-core mains lead with no earth. If someone's fitted a "safer" 3-core one, hum loops can result. (3) Does your cartridge have a little lug under one of the signal ground pin, linking this pin to the cartridge body? Sometimes, these can introduce a hum loop, as the arm is then being grounded in more than one place. (4) Have you tried removing and replacing the headshell a few times, to clear any bad connections there? (assuming yours is fitted with a Thorens arm). (5) Does the level of hum vary if you touch the arm, or if you move the arm towards the centre spindle? Nick.

1st Jun 2009, 9:34 pm	#5
qualityten Octode Join Date: Feb 2009 Location: Wallasey, UK. Posts: 1,314	Re: Thorens TD150 hum following re-wire. Thanks for latest suggestions Nick. Will check these. As promised, here is a pic of the tag connections and one of the front of the deck, just for interest. David Attached Thumbnails Last edited by Brian R Pateman; 1st Jun 2009 at 9:50 pm. Reason: Embedded images converted to thumbnails.

1st Jun 2009, 9:46 pm	#6
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,865	Re: Thorens TD150 hum following re-wire. That looks fine as far as I can tell. Where do the grey and second black wires connected to the earth terminal go? I do like the Goodmans presentation. Very 1970s styling, and much more robust than the Thorens plinth and dustcover. The latter always seems to crack. They also came badged as Leak, Tandberg and many other well-known brands. Nick.

1st Jun 2009, 10:02 pm	#7
qualityten Octode Join Date: Feb 2009 Location: Wallasey, UK. Posts: 1,314	Re: Thorens TD150 hum following re-wire. Have made the checks you suggested. None of those tweaks affect it. But, to be honest, it is pretty minimal at normal listening volume, before a record is put on. What does increase the hum is handling the cable to the RCAs. I just took a cheapish interconnect. Perhaps it is not adequately screened? David

1st Jun 2009, 10:51 pm	#9
AlanBeckett Rest in Peace Join Date: Dec 2008 Location: Burton upon Trent, East Staffordshire, UK. Posts: 1,686	Re: Thorens TD150 hum following re-wire. Nick, [There's a lot of TD150s about at the moment!] I don't remember mine, into a Leak 2000, producing any hum at all. Indeed, the first sound you heard was the usual hiss as you lowered the head on to the record. I think your idea of another amp would be a good test. Alan

2nd Jun 2009, 8:49 pm	#10
qualityten Octode Join Date: Feb 2009 Location: Wallasey, UK. Posts: 1,314	Re: Thorens TD150 hum following re-wire. Hi Nick and Alan The moment Alan said that it should be silent, I realised it must be a poor connection somewhere. I checked it with another solid state amp and it turned out to be the replacement RCA cable. I've just put a replacement in and it's dead silent. Result! Now I just need to source the missing outer platter, probably from the usual dodgy sources. Many thanks to you both, and apologies to the moderator for giving him some work. David

2nd Jun 2009, 8:53 pm	#11
Nickthedentist Dekatron Join Date: Jan 2005 Location: Oxford, UK. Posts: 17,865	Re: Thorens TD150 hum following re-wire. Well done!

2nd Jun 2009, 9:11 pm	#12
AlanBeckett Rest in Peace Join Date: Dec 2008 Location: Burton upon Trent, East Staffordshire, UK. Posts: 1,686	Re: Thorens TD150 hum following re-wire. Splendid!