Interconnect conundrum

[farflungstar]

I have a question....

I need to buy 2 pairs of interconnects, 1 between SUT and phono, the other between phono and linestage.

I've been taking with Paul at RFC as I know his cables have an excellent reputation. Paul has recommended Pluto for SUT to Phono and maybe Mercury or Venus for phono to linestage.

But here's my question... The Pluto isn't as refined as the top mercury and Venus, and doesn't have their ultimate resolution of fine detail. So, if the Pluto is losing information what's the point of putting a higher resolving cable after it - information will have been lost beforehand - no?

Paul says that the mercury and Venus aren't suitable due to their capacitance - so should I be looking for a better cable to go between SUT and phono?

[walpurgis]

Paul is the one to answer this Adrian. Speak to him again to gain some clarification.

[Infinitely Baffled]

I wouldn't worry. I very much doubt that you will hear any difference.
IB

[farflungstar]

I've been speaking to Paul about it and he's been incredibly helpful. I guess it's more complex than I suggested in my post but my thinking and methodology has always been to have the purest source possible and then try to maintain that down the chain. Knowing that there is a cable above the Pluto that has more finesse and fine resolution in my (maybe topsy-turvy) world means it should go first. Just frustrating that capacitance means I can't.... Hence my question about a better cable from another maker followed by Paul's Mercury or Venus.

I hate buying bloody interconnects!

[Stryder5]

Can anyone answer what difference does capacitance have on IC cables, and why do they differ in different position in the chain?

[Reffc]

Can anyone answer what difference does capacitance have on IC cables, and why do they differ in different position in the chain?


Capacitance is really only an issue between MM cartridges and phonostages. Many (not all) MM cartridges work well with lowish total capacitative loading, in the region 150 to 350pF total. If you have a cable with capacitance of say 150pF/m and a 2m run to the phonostage, you already have 300pF before you count the plugs (5pF per plug usually), and the tonarm cable (another 20-50pF or so) then there's the phonostage loading. Many use a standard load on the input for MM of 150pF. Some don't use any. If you take the 150pF case, then you may end up with a total load of about 520pF which, cartridge depending, may be enough to cause quite an audible roll-off in response.

For that reason, it is usually sensible and desirable to keep cable capacitance as low as possible between MM output and phonostage.

It's not always an issue between MC outputs and SUT's or phonostages, as capacitance may not be quite as important a consideration here (post edit: providing that the SUT's design means that cable capacitance won't be detrimental, but always safer to stick with lower capacitance cables in such cases anyway).

It's also not so much an issue at the source output from line level as that can drive reasonable lengths. E.g. At line level from pre or from phonostage/DAC/CD outputs, it's pretty much a non issue and you can get away with fairly long lengths providing that you keep geometry sensible and don't use unusually high capacitance cables.

[farflungstar]

Paul, are you saying that the mercury would be OK between my MC cart/SUT/ MM input in phonostage?

[bronzeage]

I can't comment about the specifics of your situation, although I do understand you want the best cables in place along the whole chain.
What I can say is, Paul has never given bad advice - if he says the Pluto is the best cable for the job, then I would believe him.
Maybe you could have a Pluto cable with the Venus super-dooper plugs?
I have yet to come across a better set of plugs than those, and they do make a significant difference (at a price).
Maybe Paul does not think that it is worth it for its position, or there is some technical reason not to do so - I'll let him comment.

[hifinutt]

i have used the pluto in 24 k worth of amplification and still do . its a superb interconnect . i was using some high end interconnects and paul made some hyperion the other day . pretty damm good for 100 quid and he is highly recommended for care and attention to detail

save your money for better boxes

[Reffc]

Thank you for your kind comments chaps.

Ade, the reason that I recommended the Plutos for your situation is that I believed they'd give the best VFM and performance in your particular case. Being unfamiliar with your specific SUT, I don't know whether it uses (for example) any specific series zobel across the secondary windings to control HF ringing as some do so I suggested the least reactive cable for that situation. For most SUT's it's not an issue and the Mercury may or may not have advantages depending on length (for shorter lengths where capacitance is not an issue, there's little advantages, but for much over say 1.5m lengths, I'd recommend the Mercury as the design in theory results in slightly better S/N retention). After your phonostage, between it and your amp, the Mercury is the one I would recommend. The Pluto and Neptune are my go-to cables for most phono applications using modest lengths because they are very low reactance and well shielded. I've send a private e:mail explaining this further for you.

[dimkasta]

About cable capacitance, the low pass filter created with the output impedance of the source is usually way above the audible frequency region for most decent devices. Unless you are using something like a passive attenuator, or a valve pre with silly output impedance. So the effect of the filter should be negligible for line levels as Paul already noted.
Cart loading was already explained nicely by Paul.

I have however noticed that low capacitance interconnects tend to sound better in general. Perhaps it's a sign of better design or quality, or we are underestimating the value of bandwidth way above the audible frequencies. But that is a different discussion which tends to cause flames.


So, if the Pluto is losing information what's the point of putting a higher resolving cable after it - information will have been lost beforehand - no?

Well think about it this way. All cables by definition are imperfect and should have some diminishing effect (let's consider their electrical compatibility and synergy equal for simplicity).
Then, the total diminishing effect is the sum of the effect of the two. So a better second cable should still offer a benefit (smaller total effect).

The only case that would make the quality of the second cable irrelevant, is if the first is so bad that its effect swamps any benefits from better wiring anywhere else.
But that would be a really bad cable anyway.

[RothwellAudio]

Can anyone answer what difference does capacitance have on IC cables, and why do they differ in different position in the chain?
The capacitance of a cable places a capacitive load on the source it is connected to. The nature of the source impedance determines what effect that load capacitance will have. For example, a simple passive pre-amp using a 25k pot would have a highish output impedance which would be 6.25k at its highest point (lower for other positions of the pot). That 6.25k source impedance combined with the cable capacitance will roll off the high frequencies. However, a metre of even poor quality cable will have a capacitance of only about 300pF, so the HF roll-off is still well above the audio band. It works out at about 85kHz. Anyway, it should be a nice, predictable and gentle roll-off - nothing nasty.

A capacitance load on the output of a transformer is a different matter. The output impedance of a transformer is more complex and the effects of capacitance are different from the case of the passive pre-amp. With an MC step-up transformer the effect is usually to create a peak in the frequency response before a rapid roll-off. There will also be some ringing (though in reality the two effects are the same thing). In this respect the output of a SUT is rather like that of an MM cartridge and capacitance should be kept low if possible.

Op-amps are another thing again. In basic theory an op-amp will have a very low output impedance and a capacitive load won't worry it. In practice some op-amps can go nuts into a capacitive load and start oscillating at audio frequencies or above. It's considered good practice to put a resistor of about 200 ohms in series with an op-amp's output to prevent such problems.

Anyway, the point I'm trying to make is that the effects of cable capacitance depend on where the cable is used, but as a general rule it is best to have as little capacitance as possible.

[Stryder5]

Thanks for your explanations guys, very useful.

[Reffc]

The capacitance of a cable places a capacitive load on the source it is connected to. The nature of the source impedance determines what effect that load capacitance will have. For example, a simple passive pre-amp using a 25k pot would have a highish output impedance which would be 6.25k at its highest point (lower for other positions of the pot). That 6.25k source impedance combined with the cable capacitance will roll off the high frequencies. However, a metre of even poor quality cable will have a capacitance of only about 300pF, so the HF roll-off is still well above the audio band. It works out at about 85kHz. Anyway, it should be a nice, predictable and gentle roll-off - nothing nasty.

A capacitance load on the output of a transformer is a different matter. The output impedance of a transformer is more complex and the effects of capacitance are different from the case of the passive pre-amp. With an MC step-up transformer the effect is usually to create a peak in the frequency response before a rapid roll-off. There will also be some ringing (though in reality the two effects are the same thing). In this respect the output of a SUT is rather like that of an MM cartridge and capacitance should be kept low if possible.

Op-amps are another thing again. In basic theory an op-amp will have a very low output impedance and a capacitive load won't worry it. In practice some op-amps can go nuts into a capacitive load and start oscillating at audio frequencies or above. It's considered good practice to put a resistor of about 200 ohms in series with an op-amp's output to prevent such problems.

Anyway, the point I'm trying to make is that the effects of cable capacitance depend on where the cable is used, but as a general rule it is best to have as little capacitance as possible.


Exactly as Andrew has explained, this is why I would always specify the least reactive (but necessarily very well shielded cable) between SUT and phonostage, hence the Pluto (or Neptune) would both be fine there. Ade has selected the Pluto, so all's good.

Great overall summary Andrew. Perhaps it's time some "stickies" were made for the cable area, so that these recurring queries could be addressed by a few simple explanations? Happy to contribute.

[RothwellAudio]

Perhaps it's time some "stickies" were made for the cable area, so that these recurring queries could be addressed by a few simple explanations? Happy to contribute.
I'd be happy to make a contribution but I'm not sure that what I have to say is what people want to hear. The idea that Brand X has good soundstage width but lacks control in the bass or that silver tends to sound over-etched except with valves is not one I subscribe to - and I wouldn't want to alienate forum members.

[farflungstar]

Andrew your information was very useful, nowt wrong with technical explanations.

Have ordered my cables from Paul and looking forward to receiving them[emoji3]