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-   -   Internal coaxial cable for preamp (http://www.diyaudio.com/forums/pass-labs/187797-internal-coaxial-cable-preamp.html)

Nounours18200 25th April 2011 03:05 PM

Internal coaxial cable for preamp
 
Hi friends,

I have upgraded a preamp with different (excellent) parts, each of these have provided a huge improvement in sound.
Now I would like to change the original coaxial cable, going from the preamp mainboard to the stepped volume attenuators, by a very good coax. (note that there is one coaxial for each channel, carrying [ground + signal])

What your recommendations are: I do not know many good coaxial cables...

Thank you !

qusp 25th April 2011 05:26 PM

Belden RG-405 is a good silver plated copper solid core with teflon insulation. and then depends on your budget, vhaudio make a nice one with upocc copper in teflon with spc and foil shield. you dont have to get 75ohm cable though, probably someone will come in here and tell you you should, but 75ohm is generally more suitable for external digital interconnects. imo the 50 ohm cables are more suitable for internal connections, also there is a larger range of high quality teflon insulated RF grade 50 ohms cables. look out for some nice milspec nos stuff too with 100% double spc shield.

dont bother with the furutech stuff here. are these cables terminated with resistors for impedance matching?

Nounours18200 25th April 2011 07:43 PM

Quote:

and then depends on your budget, vhaudio make a nice one with upocc copper in teflon with spc and foil shield.
I have had a look at the vhaudio site, but I have not seen the coax you talk about: there are many ohno cables but I have seen no coax... Can you give me the name of the cable you talk about ?

Quote:

you dont have to get 75ohm cable though, probably someone will come in here and tell you you should, but 75ohm is generally more suitable for external digital interconnects. imo the 50 ohm cables are more suitable for internal connections,
I fully agree...

Quote:

there is a larger range of high quality teflon insulated RF grade 50 ohms cables. look out for some nice milspec nos stuff toohttp://www.diyaudio.com/openx/www/delivery/ck.php?oaparams=2__bannerid=110__zoneid=3__cb=251a b0f1e5__oadest=http%3A%2F%2Fwww.bursonaudio.com%2F diy_audio.htm with 100% double spc shield.
if you have some URL to give me, I am interested...


Quote:

Belden RG-405 is a good silver plated copper solid core with teflon insulation.
Will have a look at it: I already have an equivalent cable, with Teflon insulation and silver plated copper, but it is not a solid core design, it is a multiconductors design. Do you believe that solid core is preferable over multistrand ???

Thanks

qusp 26th April 2011 11:00 AM

well the vhaudio pulsar Cu is 75r, but still very good, its also now available in silver upocc, but at a difference of 100 dollars per meter vs the Cu one. depends how covvitted to the cause you are :D i cannot recommend the silver as i have not tried it, though i have used the copper one to great effect.

VH Audio - Wire and Cable

sorry you'll have to search through for the nos stuff, it comes and goes. there was even some available on here for a while in the vendors area. i always use solid core over stranded unless the cable has to move around a great deal. i just ran out of some nos i score as a gift, it was 13awg and i used it happily for shielded internal power connections and speaker outputs.

Nounours18200 26th April 2011 05:25 PM

Quote:

well the vhaudio pulsar Cu is 75r, but still very good, its also now available in silver upocc, but at a difference of 100 dollars per meter vs the Cu one. depends how covvitted to the cause you are i cannot recommend the silver as i have not tried it, though i have used the copper one to great effect.
Thanks ! the problem with the Ag is not the price but the fact that I do not believe that Ag is the best choice in a preamp: I have been disappointed with Ag before, because it generates a lack of realism in the reproduction... I believe I will go to the Copper version, I feel more confident...even if it is not an Oxygen Free Copper version...

Regarding the Belden, is there anybody on this forum having already used it in a preamp ?

qusp 27th April 2011 04:39 AM

huh, occ is a step beyond ofc, not beneath it. ive found ag works well in some systems and not in others, to make such a general statement as yours is a bit reductionist imo. price would stop me in this instance, because i have all the equipment i need to make coax using my own wire (4 different sizes of ptfe tubing that slide one over the other and spc braid) but the coper is pretty reasonable so i just buy it

sandyK 27th April 2011 05:23 AM

What does the characteristic impedance of a coaxial cable have to do with audio frequencies, especially given the high impedances involved at the input to the amplifier, and the very short lengths involved ?
All you need is high quality ,low capacitance , well screened cable of a coaxial type construction, and copper wire inner conductor(s).
SandyK

stratus46 27th April 2011 07:03 AM

Quote:

Originally Posted by qusp (Post 2550741)
Belden RG-405 is a good silver plated copper solid core with teflon insulation. and then depends on your budget, vhaudio make a nice one with upocc copper in teflon with spc and foil shield. you dont have to get 75ohm cable though, probably someone will come in here and tell you you should, but 75ohm is generally more suitable for external digital interconnects. imo the 50 ohm cables are more suitable for internal connections, also there is a larger range of high quality teflon insulated RF grade 50 ohms cables. look out for some nice milspec nos stuff too with 100% double spc shield.

dont bother with the furutech stuff here. are these cables terminated with resistors for impedance matching?

Why would you think 50 ohm cable is better for running 'non-terminated'? I would think you'd be interested in the amount of capacitance per foot as that is going to form a low pass filter combined with your output resistance. Looking at Belden 8219 50 ohm coax has 25.5 pF /ft vs 1505F 75 ohm coax at 17.5 pF/ft. It's not a massive difference but it is opposite what I'd expect you to be concerned about.

RG-405 comes up 'No products found matching criteria.'.

G

googlyone 27th April 2011 08:02 AM

I hate to think of people paying 100$ a metre for coax for internal preamp wiring, but i suppose some will.
It would be nice to see the most significant aspects considered:.
ease of use (semi rigid coax might have 18ghz bandwidth but is a mongrel to work),
robustness,
sensible capacitance and
decent screening.

50 / 75 ohm coax? This is irrelevant at audio frequencies.
Gold vs silver - really aesthetics.
Solid core vs stranded - is an issue of ease of workability and perhaps more importantly robustness.
Capacitance is unlikely to be relevant except in an extraordinarily badly designed system - or maybe very high impedance valve design (though i would class this as poor )
decent screening is a real issue with cheap coax. Not only is some "coax" little more than two wires loosely bound in a sheath, the ground on some is tiny.

Sorry to poo poo the rf coax part - it is just no more relevant than the colour.

Nounours18200 27th April 2011 11:45 AM

Quote:

huh, occ is a step beyond ofc, not beneath it. ive found ag works well in some systems and not in others, to make such a general statement as yours is a bit reductionist imo.
it is also what I have experimented in different preamps (sorry if my English was not clear enough).

I have finally ordered the copper version of the coax...


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