Low capacitance audio coax
 

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

Low capacitance audio coax
 

"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

Low capacitance audio coax
 

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

Low capacitance audio coax
 

"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.

Low capacitance audio coax
 

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.

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.


1192A is 40pF per foot not per metre.

Cheers

Ian

Use a buffer. MUCH smarter.

Low capacitance audio coax
 

"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.

Low capacitance audio coax
 

"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

Low capacitance audio coax
 

"Trevor Wilson"

Belden have a cable called 1192A, which exhibits around 40pF/Metre.


** Quad core, low Z mic cable ????




...... Phil

Low capacitance audio coax
 

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.

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.


1192A is 40pF per foot not per metre.

**Mea culpa. Stupid Farnell. Stupid me. Most of their cables are listed in
XXpF/Metre, except that one.

Use a buffer.


--
Trevor Wilson
www.rageaudio.com.au

Low capacitance audio coax
 

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

Low capacitance audio coax
 

In article ,
Ian Bell wrote:
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?

Those sort of output impedances were common in valve days. Use a video or
RF coax to your requirements. Maplin sell a range by the metre.

--
*The more I learn about women, the more I love my car

Dave Plowman London SW
To e-mail, change noise into sound.

Low capacitance audio coax
 

"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.

Low capacitance audio coax
 

"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

Low capacitance audio coax
 

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

Low capacitance audio coax
 

"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

Low capacitance audio coax
 

"Dave Plowman (News)" wrote in message
...
In article ,
Ian Bell wrote:
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?

Those sort of output impedances were common in valve days. Use a video or
RF coax to your requirements. Maplin sell a range by the metre.


Hence the DIN idea of using a low input impedance at the other end of the
cable. A pretty crap idea (IMO) but as a way of reducing the HF loss from
cable capacitance it worked.

David.

Low capacitance audio coax
 

"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.

Low capacitance audio coax
 

"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.


I find it curious that you ask for help, then respond like that to a
constructive response. Why should anybody bother to help you if that's the
sort of thanks they get?

David.

Low capacitance audio coax
 

"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

Low capacitance audio coax
 

"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

Low capacitance audio coax
 

There used to be little two transistor gadgets made for exactly this purpose
back in the 70s. Final stage an emitter follower of course.
It is surprising though haw many outputs on hi fi are affected by capacity
in leads. It has to be poor design of the output circuit in my view. Not so
mbad these days, but it used to be a real pain.

Brian

--
Brian Gaff -
Note:- In order to reduce spam, any email without 'Brian Gaff'
in the display name may be lost.
Blind user, so no pictures please!
"Trevor Wilson" wrote in message
...

"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

Low capacitance audio coax
 

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.

Low capacitance audio coax
 

Dave Plowman (News) wrote:
In article ,
Ian Bell wrote:
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?

Those sort of output impedances were common in valve days. Use a video or
RF coax to your requirements. Maplin sell a range by the metre.


I keep forgetting about Maplin. I checked their catalogue and they have
an AV coax by Shark that is only 65pF/metre.

Thanks Dave

Cheers

Ian

Low capacitance audio coax
 

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.


I find it curious that you ask for help, then respond like that to a
constructive response. Why should anybody bother to help you if that's the
sort of thanks they get?

David.



I don't find comments like '50K is stupidly high' and the later comment
using the same 'stupid' word to be at all constructive.

Cheers

Ian

Low capacitance audio coax
 

On Tue, 01 Dec 2009 10:20:18 +0000, Ian Bell
wrote:

Dave Plowman (News) wrote:
In article ,
Ian Bell wrote:
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?

Those sort of output impedances were common in valve days. Use a video or
RF coax to your requirements. Maplin sell a range by the metre.


I keep forgetting about Maplin. I checked their catalogue and they have
an AV coax by Shark that is only 65pF/metre.

Thanks Dave

Cheers

Ian

Still worth adding that inductor. Have a look at the difference it
makes, assuming 2 feet of 65pF/m cable. The green solid line is
without the inductor, the blue solid line is with.

http://www.soundthoughts.co.uk/look/highx.png

The inductor here is 56mH, connected to the wiper of the pot.

d

Low capacitance audio coax
 

In article , Ian Bell
wrote:
Dave Plowman (News) wrote:
In article , Ian Bell
wrote:
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?

Those sort of output impedances were common in valve days. Use a video
or RF coax to your requirements. Maplin sell a range by the metre.


I keep forgetting about Maplin. I checked their catalogue and they have
an AV coax by Shark that is only 65pF/metre.

I've been trying to recall the type of the UHF cable I've tended to use for
general purpose audio coax. I bought a drum 25 years ago because it was
c60pF/m and worked OK. Single solid inner, foamed spaced, sparce braid
outer. Fairly high diameter but works nicely for long runs. I'd recommend
it if I could remember the type number! :-)

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

Low capacitance audio coax
 

In article ,
David Looser wrote:
Those sort of output impedances were common in valve days. Use a video
or RF coax to your requirements. Maplin sell a range by the metre.


Hence the DIN idea of using a low input impedance at the other end of
the cable. A pretty crap idea (IMO) but as a way of reducing the HF
loss from cable capacitance it worked.

But only if you have an even lower source impedance. ;-)
Easy to do with transistors. With valves you need an extra stage.

--
*Ever stop to think and forget to start again?

Dave Plowman London SW
To e-mail, change noise into sound.

Low capacitance audio coax
 

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.

Low capacitance audio coax
 

"Dave Plowman (News)" wrote in message
...
In article ,
David Looser wrote:
Those sort of output impedances were common in valve days. Use a video
or RF coax to your requirements. Maplin sell a range by the metre.


Hence the DIN idea of using a low input impedance at the other end of
the cable. A pretty crap idea (IMO) but as a way of reducing the HF
loss from cable capacitance it worked.

But only if you have an even lower source impedance. ;-)
Easy to do with transistors. With valves you need an extra stage.


Err.. no. The DIN system worked with high output impedences and low input
impedances. There was, of course, significant signal attenuation in so doing
with consequent S/N ratio implications, but it did reduce the HF loss due to
cable capacitance.

David.

Low capacitance audio coax
 

"Ian Bell" wrote

I don't find comments like '50K is stupidly high' and the later comment
using the same 'stupid' word to be at all constructive.

Well OK. But I don't find comments like "You assume too much" constructive
either, and you were the one asking for help. IME if someone is asking for a
solution it helps to explain as much as possible about the background to the
requirement. A bit of lateral thinking may provide a better solution than
the one the OP has in mind.

David.

Low capacitance audio coax
 

On Tue, 01 Dec 2009 10:32:20 +0000 (GMT), Jim Lesurf
wrote:

In article , Ian Bell
wrote:
Dave Plowman (News) wrote:
In article , Ian Bell
wrote:
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?

Those sort of output impedances were common in valve days. Use a video
or RF coax to your requirements. Maplin sell a range by the metre.


I keep forgetting about Maplin. I checked their catalogue and they have
an AV coax by Shark that is only 65pF/metre.

I've been trying to recall the type of the UHF cable I've tended to use for
general purpose audio coax. I bought a drum 25 years ago because it was
c60pF/m and worked OK. Single solid inner, foamed spaced, sparce braid
outer. Fairly high diameter but works nicely for long runs. I'd recommend
it if I could remember the type number! :-)

Slainte,

Jim

RG63 comes in at 10pF per foot; it's an air-spaced polyethylene, so
well suited to an installation like this.

d

Low capacitance audio coax
 

On Tue, 01 Dec 2009 13:00:49 GMT, (Don Pearce) wrote:

On Tue, 01 Dec 2009 10:32:20 +0000 (GMT), Jim Lesurf
wrote:

In article , Ian Bell
wrote:
Dave Plowman (News) wrote:
In article , Ian Bell
wrote:
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?

Those sort of output impedances were common in valve days. Use a video
or RF coax to your requirements. Maplin sell a range by the metre.


I keep forgetting about Maplin. I checked their catalogue and they have
an AV coax by Shark that is only 65pF/metre.

I've been trying to recall the type of the UHF cable I've tended to use for
general purpose audio coax. I bought a drum 25 years ago because it was
c60pF/m and worked OK. Single solid inner, foamed spaced, sparce braid
outer. Fairly high diameter but works nicely for long runs. I'd recommend
it if I could remember the type number! :-)

Slainte,

Jim

RG63 comes in at 10pF per foot; it's an air-spaced polyethylene, so
well suited to an installation like this.

d

Forgot - useful chart he

http://www.rfcafe.com/references/ele...coax-chart.htm

d

Low capacitance audio coax
 

In article ,
Jim Lesurf wrote:
I've been trying to recall the type of the UHF cable I've tended to use
for general purpose audio coax. I bought a drum 25 years ago because it
was c60pF/m and worked OK. Single solid inner, foamed spaced, sparce
braid outer. Fairly high diameter but works nicely for long runs. I'd
recommend it if I could remember the type number! :-)

FM radio coax that you could get easily at one time was good for this -
used it with my old Quad II setup which had high output impedances to
things like a tape recorder. It was smaller than YHF stuff so just about
fitted a phono plug.

--
*Nostalgia isn't what is used to be.

Dave Plowman London SW
To e-mail, change noise into sound.

Low capacitance audio coax
 

In article ,
David Looser wrote:
"Dave Plowman (News)" wrote in message
...
In article ,
David Looser wrote:
Those sort of output impedances were common in valve days. Use a video
or RF coax to your requirements. Maplin sell a range by the metre.


Hence the DIN idea of using a low input impedance at the other end of
the cable. A pretty crap idea (IMO) but as a way of reducing the HF
loss from cable capacitance it worked.

But only if you have an even lower source impedance. ;-)
Easy to do with transistors. With valves you need an extra stage.


Err.. no. The DIN system worked with high output impedences and low
input impedances. There was, of course, significant signal attenuation
in so doing with consequent S/N ratio implications, but it did reduce
the HF loss due to cable capacitance.

You've got me confused there. Thought low out high in was the rule. What
make would I be looking at for this? I had a Quad 3 series that used DIN
connectors throughout - but that was all low(ish) out high(ish) in.

David.

--
*And don't start a sentence with a conjunction *

Dave Plowman London SW
To e-mail, change noise into sound.

Low capacitance audio coax
 

Dave Plowman (News) wrote:
In article ,
David Looser wrote:
"Dave Plowman (News)" wrote in message
...
In article ,
David Looser wrote:
Those sort of output impedances were common in valve days. Use a video
or RF coax to your requirements. Maplin sell a range by the metre.

Hence the DIN idea of using a low input impedance at the other end of
the cable. A pretty crap idea (IMO) but as a way of reducing the HF
loss from cable capacitance it worked.
But only if you have an even lower source impedance. ;-)
Easy to do with transistors. With valves you need an extra stage.


Err.. no. The DIN system worked with high output impedences and low
input impedances. There was, of course, significant signal attenuation
in so doing with consequent S/N ratio implications, but it did reduce
the HF loss due to cable capacitance.

You've got me confused there. Thought low out high in was the rule. What
make would I be looking at for this? I had a Quad 3 series that used DIN
connectors throughout - but that was all low(ish) out high(ish) in.

Most domestic equipment in the sixties and seventies used DIN connectors
without following the DIN electrical standards.

--
Eiron.

Low capacitance audio coax
 

In message , "Dave Plowman (News)"
writes
In article ,
Ian Bell wrote:
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?

Those sort of output impedances were common in valve days. Use a video or
RF coax to your requirements. Maplin sell a range by the metre.

75 ohm RF coax is typically 50pf/m.
Of course, you could use car radio coax (even if the inner is a
distinctly flimsy). That is even lower (say 35pF/m).
Try a Google on car+radio+coax+low+capacitance. This is one of the more
useful hits:
http://209.85.229.132/search?q=cache...fe.com/phpbb2/
viewtopic.php%3Ff%3D3%26t%3D4791+car+radio+coax+lo w+capacitance&cd=1&hl=e
n&ct=clnk&gl=uk
--
Ian

Low capacitance audio coax
 

"Eiron" wrote in message
...
Dave Plowman (News) wrote:
In article ,
David Looser wrote:
"Dave Plowman (News)" wrote in message
...
In article ,
David Looser wrote:
Those sort of output impedances were common in valve days. Use a
video
or RF coax to your requirements. Maplin sell a range by the metre.

Hence the DIN idea of using a low input impedance at the other end of
the cable. A pretty crap idea (IMO) but as a way of reducing the HF
loss from cable capacitance it worked.
But only if you have an even lower source impedance. ;-)
Easy to do with transistors. With valves you need an extra stage.


Err.. no. The DIN system worked with high output impedences and low
input impedances. There was, of course, significant signal attenuation
in so doing with consequent S/N ratio implications, but it did reduce
the HF loss due to cable capacitance.

You've got me confused there. Thought low out high in was the rule. What
make would I be looking at for this? I had a Quad 3 series that used DIN
connectors throughout - but that was all low(ish) out high(ish) in.

Most domestic equipment in the sixties and seventies used DIN connectors
without following the DIN electrical standards.

--
Eiron.

That's right. DIN is both a standard for the connector and the electrical
signal. The electrical signal was effectively a current drive, going from a
relatively high output impedance (100k or thereabouts if I remember
correctly) into a relatively low (2kohm again from memory) input impedance.
Very few manufacturers applied this, Grundig and Philips comes to mind...I
had a Philips receiver with the tape ins and outs to the DIN signal standard
as well as connectors. Other manufacturers including Quad, A&R Cambridge and
Naim used the connectors but in a conventional low-out, high-in fashion.
S.

Low capacitance audio coax
 

"Dave Plowman (News)" wrote in message
...
In article ,
David Looser wrote:

Err.. no. The DIN system worked with high output impedences and low
input impedances. There was, of course, significant signal attenuation
in so doing with consequent S/N ratio implications, but it did reduce
the HF loss due to cable capacitance.

You've got me confused there. Thought low out high in was the rule.

It is now.

What
make would I be looking at for this?

Pretty much anything German made in the 50s or 60s: Grundig, Telefunken,
etc.

I had a Quad 3 series that used DIN
connectors throughout - but that was all low(ish) out high(ish) in.

Yes, but that sort of stuff used the DIN connector without using the DIN
standard.

The standard originated as a way of feeding a tape recorder from a valve
radio. In order to provide a recordable output that wasn't going to be
effected by the volume control the tape-recorder output was derived directly
from the AM detector/FM discrminator, but to minimise the loading on that it
was fed via a resistor of 100k or so. Then the "diode" input of the tape
recorder had an input impedance of around 2k. Since the tape recorders
always had adequate gain in the recording amplifier to work from a
microphone the signal loss from this form of connection wasn't a problem.

This standard dragged on in a half-hearted sort of way into the '70s when
domestic tape decks (by then often Japanese in origin) had both phono and
DIN connectors. Compared with the phono sockets the DIN had a higher output
impedance, a lower input impedance and greater input gain.

David.

Low capacitance audio coax
 

In article , Dave Plowman (News)
wrote:


Err.. no. The DIN system worked with high output impedences and low
input impedances. There was, of course, significant signal attenuation
in so doing with consequent S/N ratio implications, but it did reduce
the HF loss due to cable capacitance.

You've got me confused there. Thought low out high in was the rule.

Yes. That's what has been generally adopted for tasks like domestic audio
where the idea is that it is the voltage pattern at the input terminals of
the 'load' (destination) that defined the waveform.

The idea behind the DIN 'electrical' standard was the obverse of the above.
The approach was to define the signal waveform in terms of the *current*
pattern entering the destination. Thus it reversed the approach people are
familiar with and had low input impedances combined with high source
impedances.

For short cables in both cases the cable capacitance combines with the
source and load impedances in parallel. So the outcome is similar in terms
of the primary RC low-pass effect. But in DIN 'electrical' terms you can
think of this as being a consequence of the low load resistance meaning you
don't need to significantly change the voltage on the cable. If effect, the
load resistance is so small that you aren't having to change the charge on
the cable capacitance very much so most of the current the source injects
ends up going though the load. :-)

However that meant that all you'd really done was turn around the
requirement so you now neede a low load resistance rather than a low
source impedance if you wanted to maximise the bandwidth provided when
cable capacitance was taken into effect.

So in the end if anyone had been really worried by that it would have made
more sense to use a system that was closer to being matched rather than
idealise one of the mismatch extremes like voltage or current transfer!
Given that they were making up a new 'standard' I assume they could have
done that, but it would have meant defining a cable standard as well
as ones for source and load. Hardly rocket science, though!...


I had a Quad 3 series that used DIN connectors throughout - but that was
all low(ish) out high(ish) in.

Many people (including Armstrong) adopted the DIN plugs because they were
compact for stereo and we assumed they'd become the standard. But despite
adopting the physical plugs and sockets, stayed with the tradition of using
voltage transfer pattern. So used low source impedance and high load
impedances for optimum voltage transfer.

That said, the Armstrong 600s did have (without mentioning it in the
handbooks) a second 'tape out' with a high impedance to drive any recorders
made to the DIN electrical standard. Maybe Quad had a keymatic board for that,
but I can't recall off-hand. The usual trick was just to shove in large
series resistors at source to get to the defined current level.

Quite why DIN decided to adopt that approach I can't recall. Whatever their
theory, people ended up ignoring them. :-)

Slainte,

Jim

--
Please use the address on the audiomisc page if you wish to email me.
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Armstrong Audio http://www.audiomisc.co.uk/Armstrong/armstrong.html
Audio Misc http://www.audiomisc.co.uk/index.html

Low capacitance audio coax
 

Don Pearce wrote:
On Tue, 01 Dec 2009 10:20:18 +0000, Ian Bell
wrote:

Dave Plowman (News) wrote:
In article ,
Ian Bell wrote:
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?
Those sort of output impedances were common in valve days. Use a video or
RF coax to your requirements. Maplin sell a range by the metre.

I keep forgetting about Maplin. I checked their catalogue and they have
an AV coax by Shark that is only 65pF/metre.

Thanks Dave

Cheers

Ian

Still worth adding that inductor. Have a look at the difference it
makes, assuming 2 feet of 65pF/m cable. The green solid line is
without the inductor, the blue solid line is with.

http://www.soundthoughts.co.uk/look/highx.png

The inductor here is 56mH, connected to the wiper of the pot.

d


Looks interesting. Can you post the .asc file?

Cheers

ian