Long cables from turntable or phono stage

09-21-13: Dbphd
Last night the local Thorens expert recommended I move my Parasound JC-3 to a shelf just below my TD 124. The arm is an SME 3009 Series III with Ortofon SME 30H cartridge. Should I use a 1 meter cable even though a half meter would be sufficient? I'm thinking of using Linn Silver cable.

It appears that the Ortofon SME 30H moving magnet cartridge has a recommended load capacitance of 400 pf, which is on the high side. And your phono stage does not provide adjustable load capacitance, so its input capacitance is probably smallish, perhaps something like 50 pf or even less. I couldn't find any info on the capacitance per unit length of the Linn Silver cable, but I suspect that it is unlikely to be more than around 50 pf/foot.

So the problem you would probably have with either length is too little total capacitance. With a MM cartridge having too little load capacitance is likely to result in thinness somewhere in the treble region.

You might want to consider using, at least experimentally, this kit, which makes possible adding various amounts of capacitance. It costs $46, and is sold by DB Systems (see the "Accessories" link).

After determining the optimal amount of added load capacitance you could then install a capacitor of that value into the JC3, for each channel. Or, if you would prefer not to make any modifications to the JC3, using a pair of the capacitors that are in the kit in conjunction with good quality y-adapters would probably be a reasonable long-term solution. (IMO, that is. Other opinions about using y-adapters as a long-term solution will certainly differ in some cases).

Regards,
-- Al

Ninox, in the case you described just above my guess is that the total load capacitance would probably not be very far outside of the recommended 150-300 pf range for either setting of the Moon's input capacitance. And it's quite possible that you might even be within that range for both settings. So while I would expect the two settings to result in some difference in sonics in the treble region, both settings would have to be tried to determine which is preferable.

A point to be aware of, btw, is that the "0 pf" setting will not really be zero. It will be some small amount of stray capacitance in the connectors and internal wiring, plus some small amount of input capacitance of the circuitry. The "100 pf" setting will presumably be 100 pf greater than that amount.

Regards,
-- Al

09-22-13: Dbphd
The input capacitance of the JC-3 is about 200 pF.

Interesting. I'm surprised it's that high. The optimal load capacitance for many and probably most MM's falls somewhere in the area of 100 to 300 pf. A phono stage input capacitance of 200 pf would make it impossible to optimally match nearly all of those cartridges, the possible exceptions being those in the 250 to 300 pf area when used with short lengths of low capacitance cables.

How did you obtain that information?

Best regards,
-- Al

DB, after checking further I found the following quotes from John Curl, the very distinguished designer who as you are undoubtedly aware did the electrical design of the JC-3. The quotes appear on pages 3953 and 3956 of this thread:

There is a 100pf cap at the input to ground for the JC-3. Some criticism has made me now wonder if 50 pf might be better?

... My best guess at this time [May 20, 2013] is that the effective input capacitance of the JC-3 is 125pf or slightly less. I could drop that in half, and I might, in future. The potential advantage may not be worth much. I will think about it.

Best regards,
-- Al