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 Post subject: Turntable hum
PostPosted: 13 Mar 2019, 17:49 
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Joined: 19 Oct 2018, 15:30
Posts: 125
Location: Montréal, Québec
Hi everyone !

I’ve been reading about turntable hum in hope of finding a way to reduce my thorens td-165 hum. The hum only happens when the needle touches the vinyl. When the motor turns with the needle up, it’s completely silent. I’ve separated the cassis ground from the signal and added a ground wire according to the owners manual. When I cleaned the grounds of this wire, the hum reduced, but there is still too much for me. Also, the hum is only present with the turntable. CD and other sources are fine. Could you point me out on what could cause a hum that’s only audible when the needle is down ?

Thanks to all !


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 Post subject: Re: Turntable hum
PostPosted: 13 Mar 2019, 20:13 
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Joined: 23 Feb 2017, 02:02
Posts: 494
Don't have any exprience with turntables but could be just that poor quality design.
Some humm and noise pickup when the needle is down is might be normal.

Second could possibly be power supply, I think this is vintage turntable, maybe capacitors dry up.
Or maybe orignal design has capacitors for power supply too small.


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 Post subject: Re: Turntable hum
PostPosted: 14 Mar 2019, 12:22 
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Joined: 19 Oct 2018, 15:30
Posts: 125
Location: Montréal, Québec
There is no real power supply in this turntable. It as a synchronous motor that uses the mains frequency (60hz) to keep its speed. There originally was a cap between the hot and the neutral wires, supposedly to prevent pops when you turn the motor on and off. Maybe I could try to replace it with a new safety cap (Y2 rated wich fails open to prevent both ac wires to get shorted)


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 Post subject: Re: Turntable hum
PostPosted: 14 Mar 2019, 18:46 
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Joined: 23 Feb 2017, 02:02
Posts: 494
Yes I think that may help.
Could it also possibliy be a warned out turntable needle that needs replacing or is dirty that causing the noise?


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 Post subject: Re: Turntable hum
PostPosted: 18 Mar 2019, 11:36 
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Joined: 19 Oct 2018, 15:30
Posts: 125
Location: Montréal, Québec
The cartridge Was bought new a couple months ago. It should still be fine


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 Post subject: Re: Turntable hum
PostPosted: 18 Mar 2019, 21:23 
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Joined: 04 Jun 2008, 20:59
Posts: 3987
Location: Arizona, USA
Hi, I have some experience with turntables and yours is a good model. I only have six at present (an Empire 598, a Sota, a custom direct drive, a Pro-ject, a Philips and a Transcriptor Saturn). I also design gear both diy and commercially including a number of phonograph preamps. Anyhow. If the hum is present only when the stylus is on the record then the issue is mechanical. I would first check the motor mounts. They wear out and can be replaced. Second verify that there are no wires or assemblies touching the plinth that ought not to do so. You would be looking for something that can transmit vibrations particular from the motor to the plinth.

The capacitor is useful for spark suppression, but really doesn't have any impact on the residual hum. Inadequate chassis grounding, corroded connectors at the cartridge or with the connections to the amplifier can though.

A great source for information on turntables and associated gear is the vinylengine.com forum. Friendly and lots of folks that have Thorens.

Good listening
Bruce

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 Post subject: Re: Turntable hum
PostPosted: 19 Mar 2019, 09:01 
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Joined: 19 Oct 2018, 15:30
Posts: 125
Location: Montréal, Québec
Thanks for your answer !

First of all, I’ve been reading on the forum quite a bit in the last months, and I see you as one of the most knowledgeable people here. Your answers are really valuable to me and need no introduction.

That being said, I was looking at my stylus and found the it looks a bit crooked or slightly bent from side to side when looked from the front. It is a shure M97xE that I bought in December. Could this cause the hum I hear ? My logic tells me that if it was actually bent, one channel would be louder than the other, or ar least one of the channels would have a problem that is not (or less) present on the other.

Also, the tonearm wires and rca cables are original. Could they have to much resistance wich could cause a hum ? I am thinking of doing a complete rewiring...


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 Post subject: Re: Turntable hum
PostPosted: 19 Mar 2019, 18:01 
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Joined: 04 Jun 2008, 20:59
Posts: 3987
Location: Arizona, USA
Hi, A bent stylus is not a source of hum. It can cause other things ...like distortion and mis-tracking, but not hum. That particular cartridge is not prone to picking up external hum either. Some like ones by Grado do not have built in shields and will pick up radiated hum. The probably ancient wiring in the arm and from the base to the phono preamp or input of the amplifier can easily introduce hum. I still suspect from your description that the cause is mechanical not electrical (see below though). I would likely rewire the arm and replace any cables between the turntable and preamp or amp input. Just something that can improve the sound. These things are good to do on most vintage gear but are not likely to solve you hum problem. Now beware, I don't know your skill with handling electronic gear. Rewiring a tone arm is frequently difficult and you can damage some of the more delicate parts of the arm in the process. BTW I like to use the super flex wires from KAB Audio on the web. They can be testy when you strip the ends and solder the connectors to them. I make my own interconnects but there are many decent commercial ones available. The really cheap ones (like $3-5 each) are not going to be suitable, IMO neither are the $100 and up ones worth the price in most systems.

A question...with the turntable not turning is there still hum if you place the arm on a record? If not then for sure the problem is mechanical. If it is still there then there may be a shielding issue. The plinth may not be grounded well or the motor case ground may be faulty.

Good listening
Bruce

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 Post subject: Re: Turntable hum
PostPosted: 20 Mar 2019, 07:01 
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Joined: 09 Oct 2012, 19:43
Posts: 335
Location: Vancouver Canada
Are you sure it is electrical hum or could it be "turntable rumble" heard only when the needle is down and thus
making physical contact with the record. Help comes from using a pad like felt etc under the record on the platter.
Turntables do note have their chassis gnd connected to the electrical gnd
of the pickup,, so, there must be a separate gnd wire from the turntable chassis gnd to the preamp chassis gnd
to eliminate any pickup of turntable motor noise getting into the audio lines. Unlikely in your case since this would
be making noise all the time it is connected not just when the needle is down.


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 Post subject: Re: Turntable hum
PostPosted: 22 Mar 2019, 14:20 
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Joined: 19 Oct 2018, 15:30
Posts: 125
Location: Montréal, Québec
It could be the turntable rumble. The original mat is made of some kind of hard rubber or plastic. Not the most insulating material.

The chassis ground was originally connected to the right channel ground. Thorens provide instructions in the owner manual for what they call "hum modification". They also mention that adding a separate ground wire can be needed in some cases. I made the modifications according to the manual.

Bruce : the hum is only there when the platter turns. When it comes to audio, I do it myself. The only "difficult" part of the process is punching the pin that holds the connections between the arm and headshell out. But with an appropriate size punch it shouldn’t cause me any problem. If I was able to rebuild car engines and transmissions at the job, I will definitely be able to do this.

Once again, I really appreciate your help ! Thanks !


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