RG59 for interconnect ( disscusion )

[sakis]

To Moderation:
Please allow my post here even though its related to a cable but since the nature of the question needs to be answered from solid state people .Thanks .

We are having a discussion in a Greek forum about using RG59 family cables for line level or audio signal generally ( obviously there is no question about spdif or digital signal )

I stand against that and i base my argument on that RG 59 cables meet specification to applications that are terminated at 75 Ohms generally. If cable is terminated to 22 to 100k input imp. which can be the input of one amplifier is way out of specification and behavior of the cable is expected to be unpredictable .

As far as i know there is no documentation on Belden cables for example or suggestion to recommend the cable for audio use also .

Obviously the cable will play but how well and what drawbacks might have i don't know .

I d like to here opinions please and the most welcome will be the ones coming from documentation

Thankful regards
sakis

[jez]

As interconnect cable has no sound of it's own, any screened cable should do
I'm just off to board up my windows and lock the doors....

[sakis]

hmmm are you sure about that?

Rg 59 presents a capacitance of 21pf per feet ...would you like to know what exactly will do a capacitor of 100pf in the input of on amplifier that features impedance of 100K ?

how about a filter at 15.9 KHZ ?

let us not forget that the predicted capacitance of 21pf per feet probably applies when cable is properly terminated at 75 ohms Obviously if the cable is terminated at 47k or 100K specs might be by far different...

think it over ....it might not be exactly like that

( or may be the way i think is wrong and someone has to explain to me please )

[jez]

Originally Posted by sakis

hmmm are you sure about that?

Rg 59 presents a capacitance of 21pf per feet ...would you like to know what exactly will do a capacitor of 100pf in the input of on amplifier that features impedance of 100K ?

how about a filter at 15.9 KHZ ?

let us not forget that the predicted capacitance of 21pf per feet probably applies when cable is properly terminated at 75 ohms Obviously if the cable is terminated at 47k or 100K specs might be by far different...

think it over ....it might not be exactly like that

( or may be the way i think is wrong and someone has to explain to me please )

The capacitance on the input of an amp should have no effect on the amp itself.... The effect on the driving pre amp is another matter.... I think that is what you meant?
No decent pre amp should have an output impedance of any more than 1K which would then make it 1.59 MHz yes? I don't think we can hear a roll of at that frequency!
I was really just throwing stones at a wasps nest anyway Sakis !
P.S did you get anywhere with that CD player?

[sakis]

do you mean the audio alchemist ? if so i think yes i got my way around it ...i found soldering issues in the board down under the pickup fixed many of them on smd IC got a lot better but not perfect ..as we speak i am waiting to get a new transport fit it in and see how it goes ...

in a gig ...i run out of cables Guitar cables .....i was too faraway from any shop to get a cable so the only thing available in my car was 3 meters of RG 59 cable ...i solder quickly 2 Jacks on it and i give to the Guitar player .... when the player crank up the Guitar the sound was awful and what really troubled me is that when i touched the cable it actually worked as a mike ...Tap your fingers on it and you can hear the tap on the amp also ....
Can you explain that ?

[v4lve lover]

bad soldering RG59 is fine . BNC outdoes everything in use for audio hell yeah it even simlifies amplifier measuring abit

[jez]

Originally Posted by sakis

do you mean the audio alchemist ? if so i think yes i got my way around it ...i found soldering issues in the board down under the pickup fixed many of them on smd IC got a lot better but not perfect ..as we speak i am waiting to get a new transport fit it in and see how it goes ...

in a gig ...i run out of cables Guitar cables .....i was too faraway from any shop to get a cable so the only thing available in my car was 3 meters of RG 59 cable ...i solder quickly 2 Jacks on it and i give to the Guitar player .... when the player crank up the Guitar the sound was awful and what really troubled me is that when i touched the cable it actually worked as a mike ...Tap your fingers on it and you can hear the tap on the amp also ....
Can you explain that ?

Piezo-electric effect related to the dielectric of the cable... only a problem with very high impedances
Hope it works out with the CD player

[sakis]

Originally Posted by v4lve lover

bad soldering RG59 is fine . BNC outdoes everything in use for audio hell yeah it even simlifies amplifier measuring abit

cannot be a soldering issue ...its pretty straight forward ... if its not soldered properly the guitar will not play at all....there is no chance that it plays bad due to soldering issues

[sakis]

Originally Posted by jez

Piezo-electric effect related to the dielectric of the cable... only a problem with very high impedances
Hope it works out with the CD player

that sounds more like it

( i will try to keep you posted about the player just for the fun of it )

[DF96]

RG59 is 75ohms characteristic impedance at RF and somewhat lower frequencies. Its distributed shunt capacitance will be around 21pF/ft whatever termination it has - the capacitance is a property of the cable, not the termination. Similarly, it also has a fixed distributed series inductance.

It will not be 75ohms at most audio frequencies, because at low frequencies the series resistance dominates over the inductive reactance so the characteristic impedance rises and become reactive (capacitive, I think). Fortunately this does not matter unless the cable is very long - much longer than a typical interconnect. All that matters is that the total capacitance does not load the source impedance too much. The terminating resistance can be quite high. Regarding an audio cable as though it is an RF cable is a common mistake made by audio people.

So I guess the quick answer is that RG59 is not a 75ohm cable at audio frequencies, but that does not matter as impedance matching is not required.