DIY Schroeder Tonearm?

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#283
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.
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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 😀 ).
 
#285
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

MRupp said:
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 😀 ).
Click to expand...
 
#288
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
 
#289
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

MRupp said:
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
Click to expand...
 
#290
Jeffrey Davison said:
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
Click to expand...

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.
 
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#291
When I tried one braid for a DIY arm I made all warned me that there would be some cross-talk, but it turned out that it was not so.

Then I tested the twisted wire to hear the difference but I heard non at all between these two. I have no measuring equipment, but I think the signal is so weak from the cartridge there will be no interference.

I tried to braid them tight and lose do not braid tight the cable will be dull and boring medium to lose is preferable. To tight are to stiff and interupt the movment of the tonearm too.

Anders


Jeffrey Davison said:
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
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#292
Interesting picture..... In this arm, it appears that Frank has intertwined the left and right channels into a single quad braid.......

Frank, care to comment?


Jeff
 

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#294
Almost all arms twist all the wires together because it's easy to do and most arm manufacturers are mechanical engineers not electronics engineers. However, twisting the channels individually as pairs works better IF you have a proper balanced input. That means either a balanced transformer or a differential electronic input. Star quad would be even better but I doubt if it's necessary. After all, most people manage adequate results with single-ended inputs; a balanced input with twisted pair is very nearly immune to everything. Star quad is used in TV studios when you need to run long microphone cables next to lighting cables driven by dimmers.

And yes, I take each channel as a twisted pair from cartridge to transformer input. I don't get hum. Not even if I put a finger on one pin of the cartridge at full volume.
 
#295
On my systems I don't run balanced, but I do run complete S.E. dual mono. Also, I'm running a high GM input tube (6C45S) all tube phone pre, with 3 gain stages, the 6C45S, then an LCR RIAA, then two stages CCA's with no input transformer (70 db gain and no hum).

JD

EC8010 said:
Almost all arms twist all the wires together because it's easy to do and most arm manufacturers are mechanical engineers not electronics engineers. However, twisting the channels individually as pairs works better IF you have a proper balanced input. That means either a balanced transformer or a differential electronic input. Star quad would be even better but I doubt if it's necessary. After all, most people manage adequate results with single-ended inputs; a balanced input with twisted pair is very nearly immune to everything. Star quad is used in TV studios when you need to run long microphone cables next to lighting cables driven by dimmers.

And yes, I take each channel as a twisted pair from cartridge to transformer input. I don't get hum. Not even if I put a finger on one pin of the cartridge at full volume.
Click to expand...
 
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#296
Hi Jeff,
The braid has two functions. Lowering succeptability to hum and, more importantly, making shure that the wire, once inside the armwand, can't "flop around". The double twisting is a viable option, but with low impedance carts running into a balanced(or even unbalanced) high impedance input, hum will only become an issue if you placed your turntable too close to a hum source, like a mains transformer(not a good idea in any case....).
Plainly twisting 4 wires(most often found) will reduce RFI interference to a degree, but doesn't do much against hum(unless it has A LOT of turns per cm, like Nordost Valhalla).
It will increase crosstalk as well, but all carts a way worse in that department, particularly above ~7kHz, where capacitive coupling comes in.

Cheers,

Frank
 
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