Why the 1-meter limit on interconnects between the Seduction and pre-amp?

[vynyltap]

I've been able to arrange my equipment so that I can limit to a 1-meter interconnect.  I'm just curious as to why it would be a requirement.  FYI - my associated equipment are Ultimate Cables Silver Series C4 Interconnects going to a Cayin A-88t integrated amp that has an input impedance of  100k-ohms.

[Paul Joppa]

The Seduction output impedance is fairly high - 4K or 5K approximately. Cable capacitance will require extra current from the output stage at high frequencies, so the short cable is intended to minimize that extra current. Incidentally, the output stage and its limitation are the same in the Eros.

There is a substantial margin built into that requirement; the measured frequency response and power response won't be affected until the cable gets pretty long, 5 to 10 meters I would guess. But most careful listeners find some subjective loss of treble cleanliness and detail long before the simplistic measurements show an audible frequency response loss.

I've designed two RIAA preamps with greater drive capability, both needed an extra stage to do it. One had a cathode follower, the other a line driver with output transformer. It can be done if you need it, but it can't be done without at least a little sonic price to pay.

[Grainger49]

I've been able to arrange my equipment so that I can limit to a 1-meter interconnect.  I'm just curious as to why it would be a requirement.  FYI - my associated equipment are Ultimate Cables Silver Series C4 Interconnects going to a Cayin A-88t integrated amp that has an input impedance of  100k-ohms.

PJ probably answered this to your satisfaction but...  I asked a very similar question a little while back on the old forum.  I wondered how low was a "low capacitance" cable.  Most good commercial cables qualify.  I have made some long cables out of Belden 9259 cable (now 89259) 17pF/Ft.  That is well under his quoted "low capacitance" as is the Cardas I use (19pF/Ft) between my Seduction and FP 2.  Just a little more information.  

[Grainger49]

This is the text from Paul's post on high frequency roll off and Seduction:

"1000pF would give -3dB at 40kHz, or -1dB at 20kHz. That's probably the limit. But many claim to hear subtle problems with 1/10th that capacitance, typically in "passive preamp" applications. I don't know why - possibly they are hearing the dielectric of the cable? - but it seems a good rule of thumb, to be cautious with more than 100pF on a Seduction or Eros output."

The figures he quotes is for the total capacitance of the cable and the preamp input.

Two things are worth noting here, cables are rated in pF per foot, so multiply by the cable length and a roll off of 1dB at 20k Hz is inaudible.

[Len]

 I have made some long cables out of Belden 9259 cable (now 89259) 17pF/Ft.  That is well under his quoted "low capacitance" as is the Cardas I use (19pF/Ft) between my Seduction and FP 2.

Hey Grainger, do can you post info on the cables you made? I'm at the cable making stage.  I've been using triple wound lengths of Myron Toback's pure silver wire covered in teflon tubing for each strand, but I need something a bit more durable now that things are coming together. Thanks.

[Grainger49]

For years I used Belden 9259 which has been re-nunbered 89259.  The center is stranded and needs to be tinned before soldering.  The shield is braded copper not foil.  So that solders well.

The specs are here:

http://www.bluejeanscable.com/pages/technicaldocs/89259tech.htm

Blue Jeans Cable sell it at this page:

http://www.bluejeanscable.com/store/shopbycable/89259.htm

It is not the ultimate but it is good and low capacitance.  I have seen it used in some really fine systems.

[Len]

For years I used Belden 9259 which has been re-numbered 89259...It is not the ultimate but it is good and low capacitance.  I have seen it used in some really fine systems.

Thanks Grainger!

So you use coax for audio? I don't know if I have Belden 89259 at home, but I have about 40 feet of digital coax from years ago when I ordered a projection TV that never arrived. I'll check if the screen is braided. I know that back in those days I would have ordered decent stuff.

[Grainger49]

For a long time I used to cut off 6' lengths of any coax I could find at work to try as audio cables.  Nothing was as good as 9259.

Can't hurt to try whatever you have.  And fun too!

[Len]

As a rule, were they all better than twisted pair of the same quality?

[Grainger49]

I can't compare to twisted pair, I haven't used them much.  Specifically, the 9259 was preferable to Kimber KCAG between my Seduction and FP 2 because the KCAG had lots of hum.  KCAG is not shielded and I need shielded there.  

[Len]

Thank you Grainger!

Now I feel like such a moron. For my phono stage, I bought Cardas and other tweak components. Fancy wire, teflon tubing, copper braid for shielding, then fancy sleeving. This was all to construct shielded low capacitance runs within the signal chassis. I bet the 9259 is lower capacitance, better sounding, and much much cheaper!

[Grainger49]

I use Cardas Neutral Reference to the FP 2.  It is 19pf/Ft.  But sounds better than the 9259.

[Len]

I just looked up the Cardas NR. $466.00 for a half meter pair. I'll play with the 9259.

[Grainger49]

Len,

You KNOW I didn't pay that for mine.  I'm a confirmed cheapskate!