"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.

"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).


** Total ********.

Is there no ****ing stupid lie this pommy ASS will not post ????


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


Irrelevant,


** Fraid it is TOTALLY relevant to your ASININE comment.


since their frequency range is so limited

** No is isn't.

Better go check on those rampaging roos in that paddock up top.




...... Phil

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

"Trevor Wilson"
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.


** So what ???

The whole cable capacitance issue is about loss of HF response - so testing
at 1 kHz is irrelevant.

That same cart likely has a source impedance of 45 kohms at 20 kHz.


.... Phil

"Phil Allison" wrote in message
...


** So what ???

The whole cable capacitance issue is about loss of HF response - so
testing at 1 kHz is irrelevant.

That same cart likely has a source impedance of 45 kohms at 20 kHz.


The output impedance of an MM cartridge is inductive, not resistive. The
cable capacitance creates peaking with that inductance so that the overall
frequency response is reasonably flat. You cannot do this with a resistive
output impedance, so the MM example is irrelevant.

As far as we know Ian Bell's source is 50K resistive (though it might be
nice if he'd tell us what it is, instead of expecting us to guess).

David.

"David Looser is a Lying Pile of **** "


The output impedance of an MM cartridge is inductive, not resistive.

** Complete red- herring.

The signal's source impedance is high and that is the issue.


The cable capacitance creates peaking with that inductance so that the
overall frequency response is reasonably flat.

** Complete red- herring.

The signal's source impedance is high and that is the issue.


You cannot do this with a resistive output impedance, so the MM example is
irrelevant.


** Wot absolutely asinine false reasoning.

Those roos in his top paddock are having a ****ing party !!!

Leaping about a laughing at a ****ING MAD POM !!



...... Phil

"David Looser has mad 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).


** Total ********.

Is there no ****ing stupid lie this pommy ASS will not post ????


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


Irrelevant,


** Fraid it is TOTALLY relevant to your ASININE comment.


since their frequency range is so limited

** No is isn't.

Better go check on those rampaging roos in that paddock up top.

You lying ratbag.



...... Phil

David Looser wrote:
"Phil Allison" wrote in message
...

** So what ???

The whole cable capacitance issue is about loss of HF response - so
testing at 1 kHz is irrelevant.

That same cart likely has a source impedance of 45 kohms at 20 kHz.


The output impedance of an MM cartridge is inductive, not resistive. The
cable capacitance creates peaking with that inductance so that the overall
frequency response is reasonably flat. You cannot do this with a resistive
output impedance, so the MM example is irrelevant.

As far as we know Ian Bell's source is 50K resistive (though it might be
nice if he'd tell us what it is, instead of expecting us to guess).

The booklet that came with a Shure cartridge claims 1550 ohms and 650
millihenries.
So it looks like everyone is right, including Phil. :-)

--
Eiron.