[chbot] Measuring capacitance of audio cables

[hamster]

Hi Paul, 

I doubt you will be able to measure this directly, especially over a
meter or two of cable. And 1m cables don't act as transmission lines
until the signals are well in the MHz range. 

Assuming a 300 ohm source impedence, and 100pF cable capacitance, the
-3db frequency is around 5 MHz. 

(Rough numbers from
https://www.diyaudio.com/forums/parts/285128-measuring-capacitance-rca-cables.html
) 

However, I can either lend or you can come around and use my Analogue
Discovery 2. It has a Vector Network Analyzer function. that injects a
test signal and lets you measure gain and phase of the thing under test.

https://reference.digilentinc.com/learn/instrumentation/tutorials/waveforms-network-analyzer/start


If you want, I can get something like
https://www.jaycar.co.nz/2-way-phenolic-rca-socket/p/PS0263 to make up a
test jig ( 300 ohm source resistor, 10kOhm load resistor, test points). 

I just worry that getting a "no result" is very uninspiring, and we all
expect that pretty much all RCA cables are much like each other. 

Mike. 

On 08.09.2020 09:38, Paul Willmott-Dalton wrote:

> Hello all 
> 
> I am trying to support my 14yo boy with his homework but am a bit out of my depth. He is aiming to demonstrate understanding of the scientific method. To do this he wants to make a comparison of the electrical properties of different brands of audio cables. His hypothesis is that there is no difference between 'audiophile' cables vs cheapies. 
> 
> I under that folks talk about capacitance being a variable. I'm told that this will be very small in any cable and potentially difficult to read (in the tens of pF range). 
> 
> Does anyone out there have the equipment necessary to do this? If so, could we bring some cables to you for testing? 
> 
> Kind regards 
> Paul Willmott Dalton 
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