NAP / 500 / Loud Speaker - Capacitance and Inductance

Hi-Fi Corner
1

So getting a little frustrated with the explantion on why I must use recommended cables from Naim.

I see that it is almost impossible to find the technical specs of the Super Lumina vs the NAC-A5 speaker cable. However, I see hosted on the Naim website, this article: https://www.naimaudio.com/sites/default/files/HFN_Naim%20SL%20HiRes.pdf

Which states:

66.4pF per metre capacitance
0.74µH per metre inductance

vs

NAC-A5

16pF per metre capacitance
1uH per metre inductance

So the capacitance is over 4 times more and presumably this goes up with cable length. I really wish Naim would publish what are acceptable ranges for LS cables - according to the output stage design. Moan over.

2

It’s the inductance that is the critical component AIUI.

3

With what - the aim of a lower value or a higher value here?

For example my cable is:

0.13uH per foot (0.426 uH per metre (0.13 * 3.28084))

4

I assume that you want a lower figure in general but the amp still needs some load… (I’m using 4 Ohm speakers for example)

5

The amp need to see a minimum inductance of 3.5uH per channel to be stable. Optimum is around 5-10.

6

That would suggest that my 4m SL cables are not stable. They sound stable to me. It’s most confusing.

7

So forgive me lack of knowledge, can I assume that for every metre you have of cable per channel this figure acts as a multipler e.g.

Cable inductance is 0.74uH per metre. I need approx 5m to be inline with your 3.5uH.

8

I’m on!y going off what Naim recommend. It should be in the FAQs somewhere.

9

But the question is, is 0.74 per positive and negative wire, so in affect a single channel is 1.48. This could mean that you only need approx 2.2M per channel with SL to be stable and in-line with your 3.5uH figure.

10

https://community.naimaudio.com/t/speaker-cable-for-naim-power-amplifiers/87/2

11

I agree, but SL is around 25% less inductance than the NAC-A5. That is a big difference comparatively, so that really doesnt answer what the acceptable ranges really are according to the output design.

It would of been far simplier to say: Within this range e.g. 0.3 to 1.4 is OK providing that you have meterage of xx (hypothetically)

12

My underlining suspicion is, this means you have to buy Naim LS to be “safe” but not “better” according to materials, insultation, etc

13

No that is not correct, you don’t double up pos & neg.
The review said it measured loop inductance which is the correct standard,
I just wonder if Naim agree with that result & what method they used.
Whatever the 0.74uH/m is more than the average inductance & as the amps have all moved on over a few design cycles since the first days of NACA4 & 5, I wonder how important the 3.5uH per channel actually is these days

14

Yeah, I asked support and got a very unhelpful answer. I just want to know if these cable specs meet the amp design spec or not. Surely they know what is inherently stable and what is not. I’m not asking will it sound good, just im not going to blow the output stage!

15

That was a 7m cable and they measured all of it not just a metre so inductance seen by the amp was 5.18uH, I’d take a guess a 3m pair would have a different specific inductance so as to provide enough for stability.

16

With the inductance it will reduce linearly with cable length, so whether you take the loop inductance or single cable inductance, a 5m length will be 5/7 of the inductance of a 7m length.
Similarly the capacitance reduces linearly with length so a 5m length with have 5/7 of the capacitance of a 7m length.

The exception to this would be if a cable manufacturer slugged the values by putting fixed components at one end of course.
Best

David

17

With NACA5 Naim I believe state a minimum length of 3metres per channel

18

3.5m per channel. See the forum FAQ for more info.

19

I stand corrected Richard thank you, it’s in my user manuals but my recollection was incorect

:grinning:

1 Like
20

Managed to pick-up some SL on ebay - 7m length (not come yet). Anyone know what guage / diameter the wire is? I need to run it through a floor cover.