DIY Schroeder Tonearm???

[Jeffrey Davison]

Very interesting graphic representation of magnetic flux / fields interaction:
K&J Magnetics - Magnetic Fields

[Jeffrey Davison]

An interesting PDF on "potted" magnets...

http://www.goudsmit-magnetics.nl/fil...potmagneet.pdf

and a pull calculator....

http://www.kjmagnetics.com/calculator.asp

[MRupp]

perhaps if you twist pairs + and - for each channel, then the external ground/shield would not be neeeded, as twisted pairs have a shielding effect.

FWIW: If you are interested in reduced RF interference you could off course use a star-quad arrangement of the tonearm wires, i.e. +-+- for each channel. Compared to a twised pair you will get another 20dB of noise rejection, off course at double the cable cost.

Nonetheless I am surprised that you do not see this arrangement even in high end tonearms where cost should not be an ojective, though van den Hul does recommend star-quad topology (and would be selling twice the length in cable along with it ).

[binspaul]

Hello Martin,

The start-quad concept seems interesting....

Best regards,
Bins.

[Jeffrey Davison]

I will be doing up a star quad interconnect from the juction box rca's to my phono stage.

What limits me from doing a star quad is that it will require a pair of star quads through the tonearm proper. That means it's twice the thickness and probably very difficult to thread through the tube. Also, where th wires exit is importatant because they will have more force upon the free rotation of the arm and could interfere with the anti-skate settings and if too stiff, also cause mistracking... true we're talking about 32ga. wires, but having a total of 8 exiting the arm gives me a bit of pause. If we were to go a finer gauge, then the workability becomes a factor also...probably impractical .

Jeff

Originally Posted by MRupp

FWIW: If you are interested in reduced RF interference you could off course use a star-quad arrangement of the tonearm wires, i.e. +-+- for each channel. Compared to a twised pair you will get another 20dB of noise rejection, off course at double the cable cost.

Nonetheless I am surprised that you do not see this arrangement even in high end tonearms where cost should not be an ojective, though van den Hul does recommend star-quad topology (and would be selling twice the length in cable along with it ).

[binspaul]

JD,

You are absolutely right. I too is having a 32 AWG wire. What about having a simple shield using a bare wire wrapped around the twisted pairs so that it will act as an antenna ?

Best regards,
Bins.

[K.A.B]

I made my own braided tonearms cable with good results with Cardas 33 awg wire.
Then a couple years back I have seen cardas do the same and there are a shielded version too Dedicated Audio - Cardas 33AWG Braided (4) Conductor Tonearm Cable
Take Five Audio - Canada's Online Source For High-End Audio, Parts and Accessories - Cardas

Anders

[MRupp]

Several years ago I rewired my Thorens TP-90 tonearm (TD 2001 table) with a pair of star-quad cables made from Van den Huls MCS - 150 M (not as expensive then as it is now); the external diameter per single wire is 0.25 mm, so 0.5 mm per cable and it does not seem to be impeding the movement of the arm. Also, twisting the four wires together was much easier than I had first anticipated so it should be easy to do even with very thin wire.

Regarding the braided version that Anders is mentioning, I cannot comment other than to say that mine is not braided but twisted. I am not sure how much difference this makes but the idea of the twisted star-quad is that the ("electrical") centre of each pair of conductors (i.e. ++ / -- is exactly in the middle of the cable so that both are overlapping, same as in a coaxial cable, which then explains the reduction in noise pickup. The 20 dB figure is actually from an AES lecture by Bill Whitlock of Jensen transformers which I found on the WEB - and very interesting: AESUK_lecture_0705.mp3

[Jeffrey Davison]

I don't know if I'd like to braid both channels (L+R) into one braid, or even twist all 4 together. I'd be afraid of potential cross-talk between the channels.

Jeff

Originally Posted by MRupp

Several years ago I rewired my Thorens TP-90 tonearm (TD 2001 table) with a pair of star-quad cables made from Van den Huls MCS - 150 M (not as expensive then as it is now); the external diameter per single wire is 0.25 mm, so 0.5 mm per cable and it does not seem to be impeding the movement of the arm. Also, twisting the four wires together was much easier than I had first anticipated so it should be easy to do even with very thin wire.

Regarding the braided version that Anders is mentioning, I cannot comment other than to say that mine is not braided but twisted. I am not sure how much difference this makes but the idea of the twisted star-quad is that the ("electrical") centre of each pair of conductors (i.e. ++ / -- is exactly in the middle of the cable so that both are overlapping, same as in a coaxial cable, which then explains the reduction in noise pickup. The 20 dB figure is actually from an AES lecture by Bill Whitlock of Jensen transformers which I found on the WEB - and very interesting: AESUK_lecture_0705.mp3

[MRupp]

Originally Posted by Jeffrey Davison

I don't know if I'd like to braid both channels (L+R) into one braid, or even twist all 4 together. I'd be afraid of potential cross-talk between the channels.

Jeff

Maybe my previous posts were not clear, but I was NOT suggesting to use 4 wires in total, i.e. to twist both channels together. This is unfortunately the usual approach which you will see in most tomearms.

My suggestion is exactly to use 2 times 4 wires, configured as a proper star quad, i.e. 4 wires per each channel, so that there is no crosstalk between them.

P.S. On a separate note, and after listening to the AES MP3 again, the 20dB as quoted above should read "up to 40dB", though I am not sure what this is relating to, i.e. 40 db better than twisted pair or untwisted conductor pair.