I'm having to cobble together an interim phono premap solution, and I'd
be grateful for some advice.

I've got a MF LPS phono amplifier rated at 100 ohms input impedence for
the MC bit, and an AT OC9 cartridge rated at 20 ohms load impedence.

Does this matter?

If so, how do I correct it?

Thanks

Rob

"Rob" wrote in message
...
I'm having to cobble together an interim phono premap solution, and I'd be
grateful for some advice.

I've got a MF LPS phono amplifier rated at 100 ohms input impedence for
the MC bit, and an AT OC9 cartridge rated at 20 ohms load impedence.

Does this matter?

**Nope.


If so, how do I correct it?

**Don't bother.


--
Trevor Wilson
www.rageaudio.com.au

"Trevor Wilson" wrote in message
...

"Rob" wrote in message
...
I'm having to cobble together an interim phono premap solution,
and I'd be
grateful for some advice.

I've got a MF LPS phono amplifier rated at 100 ohms input
impedence for
the MC bit, and an AT OC9 cartridge rated at 20 ohms load
impedence.

Does this matter?

**Nope.


If so, how do I correct it?

**Don't bother.


--
Trevor Wilson
www.rageaudio.com.au



The 'old' electronics rule was always low Z source, high Z load, so,
as it says above, provided you have enough gain it will not be a
problem.


--
Woody

harrogate2 at ntlworld dot com

harrogate2 wrote:
"Trevor Wilson" wrote in message
...

"Rob" wrote in message
...

I'm having to cobble together an interim phono premap solution,

and I'd be

grateful for some advice.

I've got a MF LPS phono amplifier rated at 100 ohms input

impedence for

the MC bit, and an AT OC9 cartridge rated at 20 ohms load

impedence.

Does this matter?

**Nope.


If so, how do I correct it?

**Don't bother.


--
Trevor Wilson
www.rageaudio.com.au




The 'old' electronics rule was always low Z source, high Z load, so,
as it says above, provided you have enough gain it will not be a
problem.


--
Woody

harrogate2 at ntlworld dot com



Many thanks both - it certainly seems loud enough. I've just googled 'z
load', and apart from bafflement, the other variable seems to be the
cable. How do you measure the impedence of a cable?!

I'm sure it doesn't matter, just curious :-)

Rob

In article ,
Rob wrote:
Many thanks both - it certainly seems loud enough. I've just googled 'z
load', and apart from bafflement, the other variable seems to be the
cable. How do you measure the impedence of a cable?!

Doesn't matter since you're not matching in and out. And at those sorts of
impedances the capacitance won't matter either - although it can with high
impedance MM cartridges.

I'm sure it doesn't matter, just curious :-)

Cable impedance only really matters where you are matching things - like
aerials or video where they're commonly 75 ohm.

--
*Can fat people go skinny-dipping?

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

In message , Rob
writes


Many thanks both - it certainly seems loud enough. I've just googled 'z
load', and apart from bafflement, the other variable seems to be the
cable. How do you measure the impedence of a cable?!

I'm sure it doesn't matter, just curious :-)

Rob

The conventional way is to get a long length of the cable (I mean
electrically long at the frequency of interest) and then vary the
termination until you get the minimum reflected wave from the far end.
The termination that gives no reflected signal is the characteristic
impedance at that frequency. Easy to do at HF by sending a narrow pulse
down the cable and looking at the reflected pulse on a 'scope, but
essentially meaningless at audio frequencies as we never use cables long
enough for the characteristic impedance to affect things. The simple
'lumped' capacitance and inductance are all that is needed to determine
how a cable will affect the response. (Not allowing for other real
low-order effects like the piezo-electric effect, and with dielectric
absorption of course).
--
Chris Morriss

In article , Chris Morriss
wrote:
In message , Rob
writes


Many thanks both - it certainly seems loud enough. I've just googled 'z
load', and apart from bafflement, the other variable seems to be the
cable. How do you measure the impedence of a cable?!

I'm sure it doesn't matter, just curious :-)

Well, it *might* matter as in some cases the cable capacitance has an
effect when linking a cartridge to an amp.

[snip]

The simple 'lumped' capacitance and inductance are all that is needed to
determine how a cable will affect the response.

Agreed. Though if you wish you can work out the nominal cable impedance
from the L and C values (and perhaps the series resistance). This avoids
having to do an 'RF' measurement and gives a value which is perhaps more
appropriate for audio frequencies. But - as you indicate - probably a
useless quantity for most domestic audio purposes.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

"Rob" wrote in message
...
harrogate2 wrote:
"Trevor Wilson" wrote in message
...

"Rob" wrote in message
...

I'm having to cobble together an interim phono premap solution,

and I'd be

grateful for some advice.

I've got a MF LPS phono amplifier rated at 100 ohms input

impedence for

the MC bit, and an AT OC9 cartridge rated at 20 ohms load

impedence.

Does this matter?

**Nope.


If so, how do I correct it?

**Don't bother.


--
Trevor Wilson
www.rageaudio.com.au




The 'old' electronics rule was always low Z source, high Z load, so,
as it says above, provided you have enough gain it will not be a
problem.


--
Woody

harrogate2 at ntlworld dot com



Many thanks both - it certainly seems loud enough. I've just googled 'z
load', and apart from bafflement, the other variable seems to be the
cable. How do you measure the impedence of a cable?!

I'm sure it doesn't matter, just curious :-)

**With a source impedance as low as that of a MC cart, it is not important.
With MM carts, cable characteristics can be VERY important.


--
Trevor Wilson
www.rageaudio.com.au

"harrogate2" wrote in message
...

"Trevor Wilson" wrote in message
...

"Rob" wrote in message
...
I'm having to cobble together an interim phono premap solution,
and I'd be
grateful for some advice.

I've got a MF LPS phono amplifier rated at 100 ohms input
impedence for
the MC bit, and an AT OC9 cartridge rated at 20 ohms load
impedence.

Does this matter?

**Nope.


If so, how do I correct it?

**Don't bother.


--
Trevor Wilson
www.rageaudio.com.au



The 'old' electronics rule was always low Z source, high Z load, so,
as it says above, provided you have enough gain it will not be a
problem.

**Not quite. Most MC carts are designed, specifically, to be terminated with
a low(ish) load impedance. Unless so terminated, frequency response,
dynamics and distortion will all suffer.


--
Trevor Wilson
www.rageaudio.com.au

Trevor Wilson wrote:

I've got a MF LPS phono amplifier rated at 100 ohms input impedence
for the MC bit, and an AT OC9 cartridge rated at 20 ohms load

Most MC carts are designed, specifically, to be terminated with
a low(ish) load impedance. Unless so terminated, frequency response,
dynamics and distortion will all suffer.

So put a 27 ohm resistor in parallel with the input.

If the cartridge wants some load capacitance, add a bit in parallel.
The amp's input capacitance, that of the cable and your extra capacitor
should add up to the cartridge's recommended load capacitance.

--
Eiron.

This advice is worth what you paid for it.