Cartridge loading - does it matter?
 

In article , Don Pearce
wrote:


Jim, I've just been Spicing all the values I can find for both MC and MM
cartridges with their appropriate requested loads, and I've found
interesting things. The main one is that while MC carts are very
forgiving of load - including cable capacitance, MM ones aren't. Indeed
they look very marginal at the top end, varying from extremely peaky to
badly rolled off depending on actual cable capacitance. They all see to
be pretty marginal about getting to 20kHz at all. I've heard - and now
read in places - that they achieve their top end frequency response by
manipulation of a mechanical resonance and I can well believe it.

The above is generally so in my experience. Certainly the Shure MM
cartridges tend to exploit cable capacitance and have a response that is
very load-dependent - due mainly to their inductance.


Maybe this is why MC carts tend to have a top end spec that can extend
to perhaps 60 or 70kHz.

Have you done any similar sums?

Not really. When I was interested in this topic (mainly 20 years ago
:-) ) I lacked the data on details like MC coil inductance. Hence I've
only been able to do some generalisations. The snag being that this may
all be specific to individual set-ups, etc, so the generalisations may
simply not apply in many cases.

I suspect that the resistance and inductance tend to scale with the output
level. This would mean that most MCs have a much lower inductance than a MM
as their output is much lower. But I don't know how reliable such an
assumption may be.

Although reviews dismiss the inductance of MCs as being too small to
matter. I am not sure this is always the case. The example here is the
use of a transformer. A voltage step-up of x10 will cause the source
impedance seen by the amplifier to change by x100. Thus, unless the MC has
an inductance which is well below 0.01 that of a MM, using a transformer
might then lead pun to similar effects as with an MC.

The above problem won't show up with a transformerless system. However
since the inductance is in series with the EMF, it may still matter if the
amplifier input impedance is far lower than is typically used with a MM.

I'd be interested in the details of the models you have done, and the
source impedance data, etc. Do you take cabling into account?

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

Cartridge loading - does it matter?
 

In article , Nick Gorham
wrote:
Jim Lesurf wrote:


Am I correct in assuming that by "1:20" you mean the transformer's
nominal voltage step-up ratio? If so, are you using an amplifier
connected to the secondary which has an input impedance of the order
of 47k? if so, will this not put a present of the order of 1k at the
primary? If so, I also wonder about the transformed level of
capacitance seen at the primary.

Yes, the transformers turns ratio is 1:20. The secondary of this is
connected directly to the grid of a E810F, and has a 100k resistor in
parallel with the transformer secondary. The expected level of
capacitance on the grid should be in the order of 3-4pf, the connections
between the secondary and the valve base are no more than a few
centemeter, so should add little additional capacitance.

OK. I assume what what you say that you avoided co-ax between the secondary
and the grid.


An alternative way to look at the above would be to note that - so far
as the amplifier and cable on the secondary are concerned - the
cartridge's source resistance and inductance will have been
transformed by x40. Hence unless the coil inductance was very small,
this might now lead back to loading problems of the type familiar to
MM users. :-)

I think you mean x400 there Jim.

Yes, sorry about that. I did a quick calculation based on x400. Then when I
started my email decided I must have made a mistake and changed to x40
(which was wrong). A minute after sending the posting I realised my error.
:-)


When you refer to "230R" and "37R" above, do you mean these are the
values you shunt the primary with? Or something else?


No, I mean the reflected load the source sees, from 100k and 15k loads
on the secondary, If I said 230 it was a typo, the file name above gives
the correct value.

Again, I suspect the "230" was my error/typo. Probably another
manifestation of my brain not being in gear when I posted. :-)

The point this raises is that - despite the magazine reputation of MCs that
they are not 'load sensitive' - they may be in practice, particularly when
using a transformer or an amp with a low input impedance. Thus reviews
really should give source resistance and inductance values in my view.

Are there any figures for things like the capacitance levels, or other
imperfections of the transformer you use? I ask because many years ago
I did experiment with using step-up transformers for MC input but
abandoned this in favour of a low-impedance low-noise preamp. The main
reasons being risk of hum induction and transformer capacitance, etc,
introducing source and load dependent variations in response. This
was 20+ years ago, though, and the transformers I had to try may well
have been much poorer than modern ones.

I was also curious about the apparent difference in channels with the lower
load as shown in your plots.

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

Cartridge loading - does it matter?
 

On Sun, 15 Oct 2006 09:40:12 +0100, Jim Lesurf
wrote:

Although reviews dismiss the inductance of MCs as being too small to
matter. I am not sure this is always the case. The example here is the
use of a transformer. A voltage step-up of x10 will cause the source
impedance seen by the amplifier to change by x100. Thus, unless the MC has
an inductance which is well below 0.01 that of a MM, using a transformer
might then lead pun to similar effects as with an MC.

The above problem won't show up with a transformerless system. However
since the inductance is in series with the EMF, it may still matter if the
amplifier input impedance is far lower than is typically used with a MM.

I'd be interested in the details of the models you have done, and the
source impedance data, etc. Do you take cabling into account?

Slainte,

Jim

Jim,

A quick google on mc cartridge inductance yielded a small crop. An
Audio technica gave 70uH in series with 17 ohms, and a load of 20 ohms
or more. Another, the Eroica, is 12uH with 8 ohms so there is quite a
variation. As you say, the inductance tends to go hand in hand with
output level. I have made the same search for mm cartridges, and come
up with typical values around 500mH.

My model was simple - a voltage source in series with the L and C, and
a load resistor in parallel with the cable capacitance. Again I looked
around the various arm assemblies to find typical values, as well as
the recommended values.

As I say, what I found was that you can take huge liberties with the
loading of mc cartridges and the only effect is on the level. The same
is not so for mm cartridges, which appear highly resonant with cable
capacity at the top end.

The question of transformers for mc carts is interesting. A
transformer will multiply the capacitance as it divides the
resistance, so it needs to go at the amplifier end of the cable, not
the cartridge end if many nanofarads aren't to be dropped across the
cartridge.

d

--
Pearce Consulting
http://www.pearce.uk.com

--
Posted via a free Usenet account from http://www.teranews.com

Cartridge loading - does it matter?
 

"Don Pearce" wrote


As I say, what I found was that you can take huge liberties with the
loading of mc cartridges and the only effect is on the level.


Been waiting for that to show - it's all I know about the subject....!! :-)



The question of transformers for mc carts is interesting. A
transformer will multiply the capacitance as it divides the
resistance, so it needs to go at the amplifier end of the cable, not
the cartridge end if many nanofarads aren't to be dropped across the
cartridge.


Again, interesting to know - but I bet it's near enough impossible to
tell....

Cartridge loading - does it matter?
 

Jim Lesurf wrote:

Again, I suspect the "230" was my error/typo. Probably another
manifestation of my brain not being in gear when I posted. :-)

That was my typo, seemd to be a bad day for them yesterday.


The point this raises is that - despite the magazine reputation of MCs that
they are not 'load sensitive' - they may be in practice, particularly when
using a transformer or an amp with a low input impedance. Thus reviews
really should give source resistance and inductance values in my view.

Are there any figures for things like the capacitance levels, or other
imperfections of the transformer you use? I ask because many years ago
I did experiment with using step-up transformers for MC input but
abandoned this in favour of a low-impedance low-noise preamp. The main
reasons being risk of hum induction and transformer capacitance, etc,
introducing source and load dependent variations in response. This
was 20+ years ago, though, and the transformers I had to try may well
have been much poorer than modern ones.


This is all I have

http://www.lundahl.se/pdfs/datash/9206.pdf

--
Nick

Cartridge loading - does it matter?
 

On Sun, 15 Oct 2006 15:19:41 +0100, "Keith G"
wrote:


"Don Pearce" wrote


As I say, what I found was that you can take huge liberties with the
loading of mc cartridges and the only effect is on the level.


Been waiting for that to show - it's all I know about the subject....!! :-)



The question of transformers for mc carts is interesting. A
transformer will multiply the capacitance as it divides the
resistance, so it needs to go at the amplifier end of the cable, not
the cartridge end if many nanofarads aren't to be dropped across the
cartridge.


Again, interesting to know - but I bet it's near enough impossible to
tell....



Maybe.... more sums for me later.

d

--
Pearce Consulting
http://www.pearce.uk.com

--
Posted via a free Usenet account from http://www.teranews.com

Cartridge loading - does it matter?
 

On Sun, 15 Oct 2006 14:49:24 GMT, (Don Pearce)
wrote:

On Sun, 15 Oct 2006 15:19:41 +0100, "Keith G"
wrote:


"Don Pearce" wrote


As I say, what I found was that you can take huge liberties with the
loading of mc cartridges and the only effect is on the level.


Been waiting for that to show - it's all I know about the subject....!! :-)



The question of transformers for mc carts is interesting. A
transformer will multiply the capacitance as it divides the
resistance, so it needs to go at the amplifier end of the cable, not
the cartridge end if many nanofarads aren't to be dropped across the
cartridge.


Again, interesting to know - but I bet it's near enough impossible to
tell....



Maybe.... more sums for me later.

d


As I sort of suspected. Adding the transformer makes the mc more
susceptible to capacitance following the transformer, but not
preceding it.

d

--
Pearce Consulting
http://www.pearce.uk.com

--
Posted via a free Usenet account from http://www.teranews.com

Cartridge loading - does it matter?
 

"Don Pearce" wrote


The question of transformers for mc carts is interesting. A
transformer will multiply the capacitance as it divides the
resistance, so it needs to go at the amplifier end of the cable, not
the cartridge end if many nanofarads aren't to be dropped across the
cartridge.


Again, interesting to know - but I bet it's near enough impossible to
tell....



Maybe.... more sums for me later.

d


As I sort of suspected. Adding the transformer makes the mc more
susceptible to capacitance following the transformer, but not
preceding it.


Again, I would query how *hearable* this might be...??

FWIW, my stepup amp/transformers usually go on the end of the TT lead when I
user a low o/p cart and the distance to the amp will vary according to what
kit is in play at the time...??

Cartridge loading - does it matter?
 

"Keith G" wrote in message
...

"Don Pearce" wrote


The question of transformers for mc carts is interesting. A
transformer will multiply the capacitance as it divides the
resistance, so it needs to go at the amplifier end of the cable, not
the cartridge end if many nanofarads aren't to be dropped across the
cartridge.


Again, interesting to know - but I bet it's near enough impossible to
tell....



Maybe.... more sums for me later.

d


As I sort of suspected. Adding the transformer makes the mc more
susceptible to capacitance following the transformer, but not
preceding it.


Again, I would query how *hearable* this might be...??

FWIW, my stepup amp/transformers usually go on the end of the TT lead when
I user a low o/p cart and the distance to the amp will vary according to
what kit is in play at the time...??


'user'....???


(Bad case of Phonetic Phingers tonight....!! :-)

Cartridge loading - does it matter?
 

On Sun, 15 Oct 2006 19:18:12 +0100, "Keith G"
wrote:


"Keith G" wrote in message
.. .

"Don Pearce" wrote


The question of transformers for mc carts is interesting. A
transformer will multiply the capacitance as it divides the
resistance, so it needs to go at the amplifier end of the cable, not
the cartridge end if many nanofarads aren't to be dropped across the
cartridge.


Again, interesting to know - but I bet it's near enough impossible to
tell....



Maybe.... more sums for me later.

d


As I sort of suspected. Adding the transformer makes the mc more
susceptible to capacitance following the transformer, but not
preceding it.


Again, I would query how *hearable* this might be...??

FWIW, my stepup amp/transformers usually go on the end of the TT lead when
I user a low o/p cart and the distance to the amp will vary according to
what kit is in play at the time...??


'user'....???


(Bad case of Phonetic Phingers tonight....!! :-)



Ah well. The whole thing is so sensitive to actual values that I'd
have to get into detail to work that out. It is all going on right at
the top, in any case, so probably wouldn't be hugely intrusive.

d

--
Pearce Consulting
http://www.pearce.uk.com

--
Posted via a free Usenet account from http://www.teranews.com