Remove hum/buzz from Thorens TD 160 turntable

[albert3d]

Hi everyone,

I need help trying to eliminate a hum/buzz I have between my Thorens TD 160 turntable and a Denon PMA-700V amplifier. Sorry if there is any misspelling, I am not english native.
I was having problems with the turntable because it was only playing one channel intermittently and I couldn't find a way to fix it so I ended up rewiring the whole tonearm. This humming was already happening before I rewired anything, so the situation regarding the hum was the same. The problem of the channel working intermittently got fixed with the rewiring. I am now trying to eliminate the hum completely.

The current situation is:
I have the turntable disconnected from the power, and have it connected via RCA and ground wire to the amp. And there is already hum, which increases if I increase the volume of the amp. If I connect it to the power and make it spin, there is no difference. If I disconnect the RCAs from the amp, the noise disappears immediately. If I plug the CD player into the phono RCA input (to try something), there is no noise. It only appears when I connect the RCA that goes to the turntable. So I assume that the problem is in the turntable.

It is old and has a somewhat complex ground and RCA wiring, these two are the only wires I have not replaced. I am waiting for quality RCA shielded cables to arrive to replace the ones that are currently there, as I don't trust the ones that are there.

Notes:
- It is not visible in the picture, but of the five sections the connecting strip has, the center one is connected to the screw that collects all the ground wires.
- I have checked that the RCA connectors of the cable fit well and are tight to the amp. All the connectors of the capsule and the capsule holder are well fastened.
- I have tried connecting the two ground wires (LG and RG) coming from the tonearm and connected them directly to the ground so they do not go through the RCA cable and there is no difference.
- I have tried disconnecting the ground wire that connects the lower chassis to the upper chassis (it has two chassis because it has a suspension system to avoid vibrations) and it slightly increases the hum, so I have left it connected.
- If I touch with my hands the red or white wire (left and right channel) the hum increases significantly. I don't know if this is normal or if it means something I don't know. If I bring closer my hand without touching the wire, or my smartphone to these cables, also increases the noise or new ones are introduced, although less. It makes me think that it is a generalized interference of the environment, but I hope that it can be eliminated somehow.
- The ground wire that comes out of the turntable and connects to the amplifier is an unshielded wire of approx. 1mm section, quite thick.
- In all these tests I have done, the amplifier is placed in my forniture and the turntable on the floor, they are not on top of each other or anything like that.

I have ordered a Pro-Ject RCA cable with the two channels individually shielded to see if replacing it will eliminate the hum, I have it pending.

Any help or suggestions would be welcome.
Thank you very much.

I leave here a schematic of the wiring:

 

[gadget73]

Can you check to see if there is any connection from either the L or R cable shield to chassis ground? I'm wondering if you have a ground loop going on. I've had issues with metal body cartridges in metal headshells when mounted without plastic washers doing this. There should not be any connection from chassis to either shield when there is a separate ground lead like this.


As an unrelated suggestion, it might be a good idea to move the terminal strip from where it is to the fixed chassis. Hanging things off the suspended part of the table can affect how the suspension acts. Might also want to consider a thinner, more flexible wire between the fixed chassis and sub-chassis for the same reason.

might also consider twisting the + and - of each channel from the tonearm to the terminal strip. That will provide some screening and reduce the chances of hum pickup.

 

[Fishead]

On my TD-160, there is no ground wire to the amplifier/receiver/phonostage.....the ground, if I remember correctly, is connected to the right channel negative wire (green wire in my case) and that is all. (If I don't remember correctly, it is connected to the left channel negative wire.) If you connect a ground wire from the chassis to your amp, you will in all likelihood get the hum you are describing. For not being english native, you did an excellent job with the language part as well as the pictures! Congratulations and welcome to AudioKarma albert!

PS - If you haven't already, here is a great site to go to for all things Thorens:

https://www.theanalogdept.com/thorens_dept_.htm

You might be able to learn all you need to get your TD-160 back in more original condition.

 

[gadget73]

In stock form, yes the chassis ground is done through one of the audio cables. Somewhere you can find the factory instructions for how to modify it to take a separate ground wire but just from memory I think this looks like it has been done correctly. The factory instructions involve retaining the original terminal strip so it will look a little different anyway.

 

[WizardWG4]

As part of your troubleshooting you could try disconnecting the green/yellow ground wire. Not sure what country you're in but this looks like a mains ground with a three prong plug. Every turntable I've ever owned had a two prong (ungrounded) plug.

 

[Fishead]

Hey gadget, I think if I were the OP I would remove the ground wire going to the amp just to see if that fixes things. I don't believe he has done that yet, or maybe I missed something? I would do the following:

1) Remove the ground wire coming from the tonearm from the block it is currently attached to and instead attach it in the same block where the right channel ground is attached.
2) Remove the ground wire going to the amplifier altogether.

See how that affects things.

And good call, Wizard, would be good to know what country the OP is in. My TD-160 also has only a two prong power cord. That may indeed be where the problem lies.

 

[gadget73]

Hey gadget, I think if I were the OP I would remove the ground wire going to the amp just to see if that fixes things.

fair point, I didn't even notice that. If this is earthed through the mains, to the amp, and if the amp is also earthed through the mains that would be a ground loop.

Mine is also on a 2 prong cord, using the original Thorens cables, wired as it left the factory.

 

[albert3d]

Thank you all very much for your replies, I really appreciate it. I will try your tips in the next days after I receive the new RCA cables aswell, you guys shared some great ideas.

I am living in Spain, and some electronic devices have two prong plugs and ground on the side (as my turntable does, but I don't know if it was added, I bought it second hand) like this:

I have another little problem... Despite of the hum, I get a high pitch constant noise, that happens intermittently. It's not there, then all the sudden appears, stays for about 20 seconds and disappears for a while, and so on. This could be the same problem as the hum, or can it be something else? Sounds like electric interference to me. Could it be other wires that are around, like the speaker wires, a lamp wire...?

 

[tnsilver]

I leave here a schematic of the wiring:

Sorry to say, this is one gigantic mess. You need to sort this out!

Thorens classic TD-16X turntables are grounded through the right channel RCA return path (sheath). There's no additional grounding wire to connect to the amp, and if one is added on top of the stock grounding scheme - it creates a ground loop and a 50Hz (Europe) hum to complement it. You've noticed that!

This is the stock grounding scheme:

For all intents and purposes the stock grounding scheme is preferable and has a lesser potential to cause trouble.

The 5th lead coming out from the tonearm base is the grounding lead and it connects to anywhere on the main chassis. The sub-chassis (floating deck on springs) connects to the main chassis using a thin gray lead (such that is won't hinder the suspension) and the right channel return path (green lead) is grounded to the same point once! In this grounding scheme there's no room for an external grounding wire hooked to the amp or pre-amp, whatsoever.

As an alternative to the stock grounding scheme, one can disconnect the grounding through the right channel (green/ground), and connect an external grounding lead to the main chassis. This lead is then connected to the chassis of the amplifier or phono pre-amp via a designated ground lug.

In this case 'earthing' (connection of the turntable to the ground pin of the power socket) can be utilized, but care should be taken to make sure this is only done once. If the amplifier or phono pre-amp are already earthed to the power socket, there's no need to earth the turntable too. In some cases you could get away with both devices earthed, in some cases you'll get hum, it depends on your home's wiring and to which power socket you hook up stuff to, and with which circuit breaker that power socket is associated.

One more issue to note is the headshell connections. Thorens has their own connection scheme, which is different than the ROW.

Mix this up with the standard headshell wiring scheme, and you'll lose the grounding and get hum.

 

[albert3d]

Hi everyone,

Thank you all for your detailed replies. I haven't had time to work on it again until today.

Here's what I did. I tried to simplify it as much as I could, following your instructions. I hope I did it right.
Unfortunately, I still have the same hum/buzz. I recorded the noise and, as mentioned, the main hum is at 50Hz and the second most annoying one is at 9KHz.

Note that the pegs are there to hold the wires while I took the picture, and the RCA female connectors would be moved to the plinth once I have everything working.

Is this wiring correct?

Some notes:
- I think this is a mistake, but there is not a wire connecting the two chassis to anything, only the two chassis between them. The only grounding wire connected is the one coming from the tonearm to the right channel - wire. Should I connect the two chassis to the right channel - wire too? EDIT: I tried and it reduces hum, but not complitely, it's still there.
- I am performing this tests with the turntable DISCONNECTED from the main power. Just plugging the RCA cables with the turntable off, as soon as I increase the volume in the amp, starts creating the hum.
- I have replaced the old RCA cable with a new one that is shielded, but it didn't help.
- I checked the headshell wiring to my ortofon 2M red capsule and they seem to be properly connected. I tried to switch the wires and it didn't help, so I left it as it was.
- As you can see in the image, I removed the extra ground wires connecting the turntable to the amp.

I am wondering if the amplifier might be part of the problem, but I don't think so.
- If I set the amplifier to phono WITHOUT any RCA cable plugged into the phono connector, it is complitely silent. Great. As soon as I plug the RCA cables into the phono connectors, the hum starts. Even if I don't plug the other end of the RCA cables in the turntable. Is this normal?

I don't know what else to do.
Thank you.

 

[gadget73]

Connect from the chassis to the right channel ground and see what that gets you. The chassis should be grounded along with the tonearm.

 

[albert3d]

I just did it, nothing really happened...

 

[tnsilver]

nothing really happened

Because it's messy!

Move the TA wiring to the chassis (yellow arrow), wire the chassis ground to the right channel's return path (orange arrow), lift the RCA jacks from the sub-chassis (that's a ground loop) and snip off the yellow ground wire (it's an antenna at least, if it's not shorting too).

Naturally, when you mount those RCA jacks in the plinth, the orange arrow wiring will become much shorter and jacks won't ground with sub-chassis.

 

[albert3d]

Thank you again, I did all of that, and the hum is still there.
- I wired the TA to the chassis.
- I wired the chassis ground to the right channel's negative wire.
- I moved the RCA jacks outside of the turntable, so they are separated and not in contact with anything else.
- I've cut the yellow+green ground wire, even though the turntable is still unplugged from the wall plug and there's no power running through it.

Any other ideas?

 

[tnsilver]

Does it get any different when you wiggle the headshell in the armtube?
Can you show me a good picture of the cart wiring in the headshell so I can verify it's the Thorens scheme?

On that note... Judging by the color of the TA wiring, it's been rewired. Use a DMM continuity test to make sure none of the signal leads conduct with the TA ground (other than green). Also... Is it possible the TA was rewired SME style and the headshell is wired Thorens scheme?

EDIT: ...and I've just noticed the TA ground lead is black and the left channel return path is black too. It requires some mental focusing not to mix up. Was it mixed up? Test with a DMM from blue headshell lead to left RCA plug circumference. Neah, forget that. I saw a shadow.

 

[albert3d]

Does it get any different when you wiggle the headshell in the armtube?

Not really :/

Here are two views of the connections of the headshell:

 

[tnsilver]

Right. This has got to be the weirdest wiring convention I'd ever seen, but luckily and wittingly you've also showed me the connector wiring and it checks out. It's eventually bound to bite someone in the rear, if not them then possibly you in a few years. I'd redo this by the conventional SME or Thorens wiring schemes, if it was mine. Just saying.

However!!! That resin connector is shot to hell (yeah, they crumble away even without extracting them) and it looks like the audio leads may very well be shorting with the armtube. You can try to wrap some shrink around the entire connector (or what's left of it).

 

[albert3d]

- I ran a continuity test with a multimeter on the 4 headshell wires, and they are correctly connected.
- I've wrapped the resin conector with plastic tape and placed it back into the tonearm, and the hum is still there. I tried a continuity test on top of the plastic tape to see if it was isolating or not, and it isolates properly.

Right. This has got to be the weirdest wiring convention I'd ever seen, but luckily and wittingly you've also showed me the connector wiring and it checks out. It's eventually bound to bite someone in the rear, if not them then possibly you in a few years. I'd redo this by the conventional SME or Thorens wiring schemes, if it was mine. Just saying.

I'm not sure how to do that. Are you talking about the wires getting out of the tonearm and connecting to the headshell? Does the ortofon 2m red have anything to do with this?
I want to solve this mess the best possible way, so I am willing to do whatever it takes to fix it forever. Maybe if I see a picture of everything done properly I can try to replicate it.

 

[tnsilver]

Does the ortofon 2m red have anything to do with this?

No. I'm talking about the headshell / connector wiring convention. SME is top left and clockwise: white, red, green, blue - like this:

Thorens is top left and clockwise: green, blue, white, red) like this:

The white/blue and red/green are always on the same side (left and right channels).

What you have there is top left and clockwise: blue, green, white, red with the hot and ground leads cross channeled. It's very confusing.

One more thing. I had that same audio technica HS wiring kit and I've tossed it. Other than the leads not being color coded, they're too short, too thick, too rigid - but, worst of all, the connectors are way too wide. I had to squeeze them with nose pliers - and wrap the inner headshell connector with shrink, so those AT pin grabber connectors don't come in contact with it.

 

[tnsilver]

This is one of my SME rewires:

This is the piece of shrink I've wrapped around the connections:

It is p-e-r-f-e-c-t. To sound good - it needs to look good too. My experience is you never have the first without the second.