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Phono Cartridge Connections

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    Posted: 23 Mar 2022 at 5:12pm
The cartridge connection(s) to the input of your phono stage are very critical to be done right.

I have been asked to help people find why they have hum or extra noise or even radio audio coming into the inputs of their phono stage.
Most needed to check and repair/correct the connections described below.

If I have missed anything you would also check/correct, post a reply. 

First is the small cartridge wires connecting to the tonearm, they must be connected firmly and to the correct orientation... usually following a color code.

Next is the tonearm internal wires, best is using a separate ground wire inside the tonearm that connects to the metal parts of your tonearm and to the phono stage ground screw... this is the turntable ground. Some turntables also connect this to other metal parts in the mechanics inside.

The tonearm wires connect to the TT rear panel RCA connectors or direct to coaxial cables for connection to the phono stage R/L inputs.

The coaxial cables that connect the TT cartridge wires to the phono stage R/L inputs are the most critical and must be completely 360 degree shielded, end to end.

This is as agreed by all ESD / EMC engineering professionals... including those contracted to test EMC susceptibility.
  
Read the following...



Do not use any cables without a proper continuous shield connected at both ends.



Edited by BAK - 23 Mar 2022 at 5:50pm
Bruce
AT-14SA, Pickering XV-15, Hana EL, Technics SL-1600MK2, Lautus, Majestic DAC, Technics SH-8055 spectrum analyzer, Eminence Beta8A custom cabs; Proprius & Reflex M or C, Enjoy Life your way!
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Post Options Post Options   Thanks (1) Thanks(1)   Quote BackinBlack Quote  Post ReplyReply Direct Link To This Post Posted: 23 Mar 2022 at 5:28pm
I'd agree with that. Lowest level audio signal in the chain, with the most fiddly of connectors to fit to the cartridge. Soldering the cartridge connectors and phono sockets to the very fine tonearm wire is quite a task, certainly one for those with a steady hand.

Ian
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 23 Mar 2022 at 5:31pm
We've had people complain of the stereo image going off to one side.

A similar complaint was from an owner of one of our mono switched phono stages - in mono there was just a varying distorted sound.

In both cases swapping over the + and - cartridge wires to the correct way round solved their issue.

Mostly we get complaints where their other phono stage works just fine, to which I sometimes ask "why'd you buy one of ours?" The answer is "because it sounds better except for this fault." Well, we can't swap cartridge phases inside the product, and their other phono stage can't either, but neither can it do the "air" like ours, and so ours shows up their mistake.

We get a few who just keep on arguing.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote BAK Quote  Post ReplyReply Direct Link To This Post Posted: 23 Mar 2022 at 5:53pm
Originally posted by BAK BAK wrote:

The cartridge connection(s) to the input of your phono stage are very critical to be done right.

I have been asked to help people find why they have hum or extra noise or even radio audio coming into the inputs of their phono stage.
Most needed to check and repair/correct the connections described below.

If I have missed anything you would also check/correct, post a reply. 

First is the small cartridge wires connecting to the tonearm, they must be connected firmly and to the correct orientation... usually following a color code.

Next is the tonearm internal wires, best is using a separate ground wire inside the tonearm that connects to the metal parts of your tonearm and to the phono stage ground screw... this is the turntable ground. Some turntables also connect this to other metal parts in the mechanics inside.

The tonearm wires connect to the TT rear panel RCA connectors or direct to coaxial cables for connection to the phono stage R/L inputs.

The coaxial cables that connect the TT cartridge wires to the phono stage R/L inputs are the most critical and must be completely 360 degree shielded, end to end.

This is as agreed by all ESD / EMC engineering professionals... including those contracted to test EMC susceptibility.
  
Read the following...



Do not use any cables without a proper continuous shield connected at both ends.

If I have missed anything you would also check/correct, post a reply. 
Bruce
AT-14SA, Pickering XV-15, Hana EL, Technics SL-1600MK2, Lautus, Majestic DAC, Technics SH-8055 spectrum analyzer, Eminence Beta8A custom cabs; Proprius & Reflex M or C, Enjoy Life your way!
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 23 Mar 2022 at 6:12pm
Many years ago there was a test record called HiFi Sound 75 Stereo Test Record (probably 1975).

The first track is left-right signal identification.

The next track is the phase test.

Provided you hooked-up your speakers correctly, then if any of the above didn't work, you would find your cartridge was wired wrong.

The thing about the mono switch (above) was that on one channel + was swapped to - and vice-versa.

So, instead of the mono switch doing a + b/2 it was doing a - b/2, and as soon as John explained that to the blokes wife, she understood.

You see, a - b/2 (or even b - a/2) produces the stereo difference signal so cancels everything else.

It's also how sum and difference circuits used in (good old analogue) radio transmission, worked.

a + b /2 = sum (mono broadcast signal)

a - b /2 = difference (stereo broadcast signal)

Both circuits go in a box marked M+S (no, not the shop), along with a 19kHz tone generator.

M is transmitted normally, but S is transmitted at twice its frequency, and if the receiver is stereo, it will also pick up the 19kHz tone and de-mod the "upper deck", and mix it to give stereo.

Clever stuff!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote patientot Quote  Post ReplyReply Direct Link To This Post Posted: 23 Mar 2022 at 7:18pm
It's very easy to make a mistake with this stuff. Not every cartridge manufacturer clearly labels the connector pins. I've also seen instances where a cartridge has larger or smaller connector pins and the user doesn't have the wiring clips connected firmly enough.
SL-1200 MK7 (modified) + Reflex M + PSU-1 used with AT150-40ML, AT VM95ML, Stanton 680mkII + Ogura, and Shure M35X cartridges.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 23 Mar 2022 at 8:22pm
More on shielding

An all-encompassing, 360 degree shield is afforded by a coaxial cable fitted with metal bodied RCA plugs. The shield is connected to the outer terminals within each plug. When connected, both items become the same Faraday shield (1st image)

Faraday shield


Edited by Graham Slee - 23 Mar 2022 at 9:18pm
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