TD166 MkII Hum issue

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Landolaman1
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TD166 MkII Hum issue

Post by Landolaman1 » 13 Sep 2019 17:39

My first Thorens TT. Going through the usual stuff, checking everything out and all seems to be in good shape apart from an infernal hum! Aaaaagghh! I've done the hum fix as shown in the service manual but no joy. I've also wired in a new terminal block for the tonearm wires which i've checked and double checked Anyone offer any suggestions? Thanks in advance. Neil

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Re: TD166 MkII Hum issue

Post by user510 » 13 Sep 2019 19:47

It is typical that hum issues have to do with the signal path and not the power circuit to the motor. So the first area of focus is on tonearm wires all the way through and starting with the cartridge clips out at the headshell. You need a multi-meter with the ability to check continuity. With that check continuity from each cartridge clip at one end out to the rca plug at the other. If there is continuity on all wires, hot and ground, then check to make certain that the ground strap from the arm to the turntable chassis has continuity. On the Thorens there is also a ground strap from the chassis of the turntable to the output terminal. The terminal within the Thorens puts a ground strap to the ground on the left output channel. Make certain that you have that circuit intact with continuity. (tonearm body to chassis to terminal left channel ground.)

One area that trips us up often enough is having the clips fitting too loose on a cartridge pin. Sometimes it is a simple matter of oxidation on the metal of the clips, pins and rca plugs as well as oxidation on the rca inputs of the preamp we're plugging into.
Stuff like that.
-Steve

Landolaman1
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Re: TD166 MkII Hum issue

Post by Landolaman1 » 13 Sep 2019 21:44

Hi Steve, thanks for your input. Guess it's a multi meter then to track down the issue. I really should have one the amount of time i spend messing about with TT's. Got one on order so will hopefully find the bad guy before too long. Just out of curiosity i changed the cart to a high output Pioneer PC-3MC and hum gone! I'm sure that's something to do with the MC circuitry. But, i want to use a MM cart so do need to sort it. Thanks again, Neil.

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Re: TD166 MkII Hum issue

Post by raphaelmabo » 13 Sep 2019 22:29

What cartridge do you have? I know that Grado cartridges can hum on some turntables, because they are unshieled, but it's not common that other MM/MI cartridges hums. Bad contacts at the back of the cartridge?

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Re: TD166 MkII Hum issue

Post by user510 » 13 Sep 2019 23:15

Landolaman1 wrote:
13 Sep 2019 21:44
Hi Steve, thanks for your input. Guess it's a multi meter then to track down the issue. I really should have one the amount of time i spend messing about with TT's. Got one on order so will hopefully find the bad guy before too long. Just out of curiosity i changed the cart to a high output Pioneer PC-3MC and hum gone! I'm sure that's something to do with the MC circuitry. But, i want to use a MM cart so do need to sort it. Thanks again, Neil.
If the hum goes away with another cartridge then it may have been to do with ensuring positive contact between pins and clips at the back of the cartridge, -- and then just making certain there was continuity all the way back for ground and hot leads both channels.

As Raphelmabo notes we don't know the cartridge you were having issues with. But, as always check fit between clips and pins on the back of the cartridge. It will vary from one cartridge to another regarding the diameter of the output pins on its backside. Also it is worth while to clean all metals at plugs and jacks, clips and pins to be certain there is no oxidation issues. I'll use acetone to scrub off whatever gunk may be on the metal. There is a product commonly used among audiophiles called "Deoxit". This will dissolve oxidation readily. We want maximum conductivity for the signal as it passes through the wires, clips and plugs on its way into the circuitry of the phono stage.

Good about the multi-meter on order. Playing with turntables pretty much requires that we all have one.
-Steve

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Re: TD166 MkII Hum issue

Post by Landolaman1 » 14 Sep 2019 11:22

raphaelmabo wrote:
13 Sep 2019 22:29
What cartridge do you have? I know that Grado cartridges can hum on some turntables, because they are unshieled, but it's not common that other MM/MI cartridges hums. Bad contacts at the back of the cartridge?
The cartridge i'm experiencing the hum from is a relatively new Ortofon OM10. No issues with it on other TT's so i think that narrows it down to a Thorens tonearm issue. But strange that the Pioneer High Output MC worked fine with no hum at all! This also makes me suspect that it could possibly be connected to a grounding issue but for the life of me i don't understand how. Ah well, multi meter should arrive in a day or two so hopefully that will give the answer.
Thanks for the input/suggestions folks.
Regards, Neil.

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Re: TD166 MkII Hum issue

Post by theclosetguy » 26 Sep 2019 00:35

I had one of these for a while. Had no issues with hum. Then taking advice from others I replaced the original terminal strip with a better one. Hummed like you could not believe. Checked every connection a dozen times with a DVM . Not a single reason for the hum. Re-installed the original terminal strip.. No more hum.

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Re: TD166 MkII Hum issue

Post by Landolaman1 » 29 Oct 2019 17:12

theclosetguy wrote:
26 Sep 2019 00:35
I had one of these for a while. Had no issues with hum. Then taking advice from others I replaced the original terminal strip with a better one. Hummed like you could not believe. Checked every connection a dozen times with a DVM . Not a single reason for the hum. Re-installed the original terminal strip.. No more hum.
Just a quick question. I installed a new terminal strip for the signal cables. Would this need any shielding? Clutching at straws here with the hum issue. Suppose it won't hurt to try.

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Re: TD166 MkII Hum issue

Post by bernard1 » 29 Oct 2019 21:51

Landolaman1 wrote:
29 Oct 2019 17:12
Just a quick question. I installed a new terminal strip for the signal cables. Would this need any shielding? Clutching at straws here with the hum issue. Suppose it won't hurt to try.
By terminal strip, do you mean that you add RCA sockets on the plinth, so you have to plug a phono cable from those sockets to the preamp ? Or are you talking of the strip where the tonearm wires connect to the phono cable ?

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Re: TD166 MkII Hum issue

Post by Richard Coxon » 29 Oct 2019 22:43

I had a hum problem with my TD 166 mk 2 for years with various MM cartridges but the problem was solved when I mounted an Ortofon Vivo Redto the arm.

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Re: TD166 MkII Hum issue

Post by Landolaman1 » 01 Nov 2019 20:17

bernard1 wrote:
29 Oct 2019 21:51
Landolaman1 wrote:
29 Oct 2019 17:12
Just a quick question. I installed a new terminal strip for the signal cables. Would this need any shielding? Clutching at straws here with the hum issue. Suppose it won't hurt to try.
By terminal strip, do you mean that you add RCA sockets on the plinth, so you have to plug a phono cable from those sockets to the preamp ? Or are you talking of the strip where the tonearm wires connect to the phono cable ?
Hi Bernard. Yes i installed RCA sockets. These are connected to the terminal strip. And yes i use phono cables to connect to the pre amp. Also connected to the terminal strip are the tonearm wires. The terminal strip is fixed to the inside of the plinth. Can't believe this would be causing hum but you never know! Any way i'm going to make myself a "Shield" and see what happens. If anything! Interestingly MC cartridges play perfectly silently. But i don't want to use MC on this particular TT.

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Re: TD166 MkII Hum issue

Post by Turnbacktime » 17 Nov 2019 15:31

Have you tried the Hum mod in the Thorens service manual downloadable from this site. From memory involves splitting the green tone arm wire away from chassis ground on the terminal strip. I had hum on my MKII and tried various things before checking for the mod. It had actually been done but badly, very easy to leave an accidental connection.
Service manual is downloadable from this site.

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Re: TD166 MkII Hum issue

Post by Landolaman1 » 17 Nov 2019 16:00

Turnbacktime wrote:
17 Nov 2019 15:31
Have you tried the Hum mod in the Thorens service manual downloadable from this site. From memory involves splitting the green tone arm wire away from chassis ground on the terminal strip. I had hum on my MKII and tried various things before checking for the mod. It had actually been done but badly, very easy to leave an accidental connection.
Service manual is downloadable from this site.
Hi, TBT, yes the hum mod was the first thing i tried. Did nothing! However i have found a spare NOS Pioneer PC3MC which is a high output MC cart and conical stylus. Strange but no hum. I'm sure someone on this site, more knowledgeable than i in this sort of stuff, will provide the reason. Thanks for your input anyway!
Regards, Neil.

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Re: TD166 MkII Hum issue

Post by hebridean » 20 Nov 2019 19:38

As user510 Steve said make sure there's an earth wire from a metal part of the turntable chassis soldered to the tonearm wire bridge which would then continue the earthing through the thicker phono wires to the RCA jacks on the unit. Then being transferred to your pre amp with your phono cables.

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