I need to send an audio signal from a 50K ohm source over a distance of
a couple of feet in a screened cable. However, most audio coax seems to
be about 100pF/ft so 2ft of this and 50K will turn over just below
16KHz. So, anyone know a source of low capacitance audio coax?

Cheers

Ian

"Ian Bell" wrote in message
...
I need to send an audio signal from a 50K ohm source over a distance of a
couple of feet in a screened cable. However, most audio coax seems to be
about 100pF/ft so 2ft of this and 50K will turn over just below 16KHz. So,
anyone know a source of low capacitance audio coax?


**Use a buffer first. A 50k Ohm source is stupidly high. A high quality
buffer can be assembled for a few pennies.

If you must persist in using broken equipment, you could look at a variant
of RG59/U coax. Capacitances figure range from 50pF ~ 70pF/Metre. Belden
have a cable called 1192A, which exhibits around 40pF/Metre.

Use a buffer. MUCH smarter.


--
Trevor Wilson
www.rageaudio.com.au

Trevor Wilson wrote:
"Ian Bell" wrote in message
...
I need to send an audio signal from a 50K ohm source over a distance of a
couple of feet in a screened cable. However, most audio coax seems to be
about 100pF/ft so 2ft of this and 50K will turn over just below 16KHz. So,
anyone know a source of low capacitance audio coax?


**Use a buffer first. A 50k Ohm source is stupidly high. A high quality
buffer can be assembled for a few pennies.


You assume too much.

If you must persist in using broken equipment, you could look at a variant
of RG59/U coax. Capacitances figure range from 50pF ~ 70pF/Metre. Belden
have a cable called 1192A, which exhibits around 40pF/Metre.

Use a buffer. MUCH smarter.



Again, you assume too much.

Cheers

Ian

"Ian Bell" wrote in message
...
Trevor Wilson wrote:
If you must persist in using broken equipment, you could look at a
variant of RG59/U coax. Capacitances figure range from 50pF ~ 70pF/Metre.
Belden have a cable called 1192A, which exhibits around 40pF/Metre.

Note that the requirement was stated in feet (2) and the figures given are
for meters, which are about 3 feet. Divide Trevor's numbers by 3 and you
will instantly find a more satisfactory number for your application.

"Ian Bell" wrote in message
...
Trevor Wilson wrote:
"Ian Bell" wrote in message
...
I need to send an audio signal from a 50K ohm source over a distance of
a couple of feet in a screened cable. However, most audio coax seems to
be about 100pF/ft so 2ft of this and 50K will turn over just below
16KHz. So, anyone know a source of low capacitance audio coax?


**Use a buffer first. A 50k Ohm source is stupidly high. A high quality
buffer can be assembled for a few pennies.


You assume too much.

You have supplied so little information about what it is that you are doing
that all we can do is make assumptions, and Trevor's assumption seems
perfectly reasonable to me. Unless you want to tell us why it isn't.

I had been going to answer your original post to the effect that "I wouldn't
start from here" (ie, wouldn't try to send audio from a source with as high
an impedance as 50K)

No *audio* co-ax will have as low a capacitance as you think you want. Try
looking at RF co-ax instead.

David.

"David Looser has roos loose in his top paddock"


I had been going to answer your original post to the effect that "I
wouldn't start from here" (ie, wouldn't try to send audio from a source
with as high an impedance as 50K)


** Shame about all the millions of MM pick-up cartridges that seem to work
OK.

Not to mention electric guitars that use 500kohm volume and tone pots.



..... Phil

"Phil Allison" wrote in message
...

"David Looser has roos loose in his top paddock"


I had been going to answer your original post to the effect that "I
wouldn't start from here" (ie, wouldn't try to send audio from a source
with as high an impedance as 50K)


** Shame about all the millions of MM pick-up cartridges that seem to
work OK.

They may be designed to work into a 50K load, but their output impedance is
far lower (typically around 1K).


Not to mention electric guitars that use 500kohm volume and tone pots.


Irrelevant, since their frequency range is so limited.

David.

Phil Allison wrote:
"David Looser has roos loose in his top paddock"


I had been going to answer your original post to the effect that "I
wouldn't start from here" (ie, wouldn't try to send audio from a
source with as high an impedance as 50K)


** Shame about all the millions of MM pick-up cartridges that seem
to work OK.

**I just measured the output impedance of a Nagoaka OM300 MM cartridge
(common, popular cartridge from 20 years ago). I measured the output Voltage
into a standard 47k input impedance, loading down the output until I reached
a -6dB point. The output impedance is calculated to be close to 2,000 Ohms,
at 1kHz, via CBS STR130 test disk. I'd expect most MM carts to exhibit
similar output impedance figures.



--
Trevor Wilson
www.rageaudio.com.au

David Looser wrote:
"Ian Bell" wrote in message
...
Trevor Wilson wrote:
"Ian Bell" wrote in message
...
I need to send an audio signal from a 50K ohm source over a distance of
a couple of feet in a screened cable. However, most audio coax seems to
be about 100pF/ft so 2ft of this and 50K will turn over just below
16KHz. So, anyone know a source of low capacitance audio coax?

**Use a buffer first. A 50k Ohm source is stupidly high. A high quality
buffer can be assembled for a few pennies.

You assume too much.

You have supplied so little information about what it is that you are doing
that all we can do is make assumptions, and Trevor's assumption seems
perfectly reasonable to me. Unless you want to tell us why it isn't.


I was not asking for an arrogant critique of of what Trevor *supposed*
the design was. The question was simple enough as it stood.

I had been going to answer your original post to the effect that "I wouldn't
start from here" (ie, wouldn't try to send audio from a source with as high
an impedance as 50K)

No *audio* co-ax will have as low a capacitance as you think you want. Try
looking at RF co-ax instead.

David.

Ian Bell wrote:
Trevor Wilson wrote:
"Ian Bell" wrote in message
...
I need to send an audio signal from a 50K ohm source over a
distance of a couple of feet in a screened cable. However, most
audio coax seems to be about 100pF/ft so 2ft of this and 50K will
turn over just below 16KHz. So, anyone know a source of low
capacitance audio coax?

**Use a buffer first. A 50k Ohm source is stupidly high. A high
quality buffer can be assembled for a few pennies.


You assume too much.

**Nope. Just the facts. Buffers can be installed for not much money.


If you must persist in using broken equipment, you could look at a
variant of RG59/U coax. Capacitances figure range from 50pF ~
70pF/Metre. Belden have a cable called 1192A, which exhibits around
40pF/Metre. Use a buffer. MUCH smarter.



Again, you assume too much.

**Such as?


--
Trevor Wilson
www.rageaudio.com.au