Cartridge loading - does it matter?
 

"Don Pearce" wrote in message
...
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.



OK - nothing to worry a *Lowther User* then...?? :-)

Cartridge loading - does it matter?
 

In article , Don Pearce
wrote:


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.

The interesting thing (for me) in the above is that the MC inductances are
over a thousand times lower than is typical for a MM. Yet the output levels
tend to only be of the order of a tenth to a hundredth of an MM.

A x20 step-up TX would convert the above MC values into 28 mH and 4.8mH,
which are both pretty small values. The source resistances do rise, though,
to 8k and 3k2.

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.

Yes. That makes sense, and your figures support the magazines tending to
ignore this - yet then raises the puzzle of why loading should be regarded
as having any effect at all... and also Nick's curious results. Maybe this
is a non-issue with 'low output' (i.e. tiny coil) MCs, but becomes one with
'high output' MCs as they have much bigger coils.

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.

Would also need to be cautious of RIAA MM amps where the designer has
already deliberately added some capacitance to get a decent loading for the
common MM designs.

Slainte,

Jim

--
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Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

Cartridge loading - does it matter?
 

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

It's interesting that the famed Ortofon SPU cartridge had a transformer
in the headshell, (which accounted for a lot of its excessive weight).
and therefore saw the capacitance of the arm cable.

I came across a US patent No 4035737 of 12th July 1977 from John J Curl
with an electronic moving coil step-up which, if I read the circuit
correctly, had a virtual earth input, and thus loaded the cartridge with
essentially zero ohms, using the cartridge's current output. The patent
claims extremely low noise through the use of multiple parallel pairs of
transistors, and very low distortion through the use of push-pull pairs.
Although the distortion of the electronics may be low, I wonder about
that of the cartridge driving into a short-circuit.

When I get some time in the next couple of weeks, I'll try and build the
circuit and see what it does.

S.

Cartridge loading - does it matter?
 

On Mon, 16 Oct 2006 10:22:55 +0100, Serge Auckland
wrote:

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

It's interesting that the famed Ortofon SPU cartridge had a transformer
in the headshell, (which accounted for a lot of its excessive weight).
and therefore saw the capacitance of the arm cable.

I came across a US patent No 4035737 of 12th July 1977 from John J Curl
with an electronic moving coil step-up which, if I read the circuit
correctly, had a virtual earth input, and thus loaded the cartridge with
essentially zero ohms, using the cartridge's current output. The patent
claims extremely low noise through the use of multiple parallel pairs of
transistors, and very low distortion through the use of push-pull pairs.
Although the distortion of the electronics may be low, I wonder about
that of the cartridge driving into a short-circuit.

When I get some time in the next couple of weeks, I'll try and build the
circuit and see what it does.

S.

I remember that cartridge. Back in the early seventies I was given an
SPU-TE. I had to modify my arm to fit it, but eventually got it in. I
put a record on and it played the first track just fine. Suddenly it
jumped inwards and there was a loud grinding sound. I had a ten inch
steel turntable, and the leakage magnetism from the cart was so strong
that when it was close enough it sucked itself hard down onto the
turntable, wrecking the cantilever.

Given that leakage field, I'm surprised that the transformer even
worked, and was not saturated to death.

As for current drive vs. voltage drive - they are as good as each
other, and to suggest that it is driving a short circuit is simply a
voltage-centric view of what amounts to a quite normal current
connection.

d

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

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