In article , Serge Auckland
wrote:
Jim Lesurf wrote:
In article , Serge
Auckland wrote:

I recently acquired a low output (0.2mV) moving coil cartridge
(Sumiko Talisman B), for which the manufacturers' recommend a load of
40-100 ohms. I am currently running it into a load of 47k as my
standard RIAA preamp has sufficient gain, albeit with a bit more
noise than for the earlier MM cartridge, but nevertheless, perfectly
acceptable. My question is:- as MC cartridges are voltage sources
(and Sumiko's manual also says) then why should the load matter once
it is, say, 10x greater than the source impedance of the generator,
which in my case is 5.8 ohms. The sound I'm getting seems fine, so I
would like to know what change/improvement I should expect from a
lower impedance load.

Any changes would depend on details you have not given (and presumably
are unknown to you).

A lower amplifier input impedance might also provide lower noise.

As the amplifier is seeing 5.8 ohms, would a lower inpedance make any
difference to the noise?

Probably not - depending on the reliability of the assumptions being made.

Couple of points as examples:

Firstly, is the source impedance genuinely '5.8 Ohms'? If the coils have an
inductance which is high enough it might cause the source impedance to be
somewhat larger than this value across some parts of the audio band.

Secondly, if the user was to employ an amp designed with a low input
impedance (as distinct from simply fitting shunt resistances to an amp with
an inherent high input impedance) then they might get a lower noise level,
and improved SNR.

e.g. compare a low-noise FET input amp with an inherently high input
impedance with something like a common-base bipolar amp. Their en/in ratios
will probably be very different.

If the source impedance is low, and resistive, then I wonder why changes in
occur the frequency response as the loading is altered... If this is due to
the effect upon generator 'compliance' then it seems efficiently coupled.




Since no source will be an ideal 'voltage source' a lower load may
also change the frequency response, or distortion, or some other
parameter. Perhaps even alter the compliance to a small extent.

At some point the coil inductance, etc, may cause a resonance.
Probably well above audio, but might make something like RF pickup
more possible in some circumstances.

But none of the above may apply in your specific case.

I am sure you are right that lowering the load impedance will make a
difference. My question was about what sort of difference, and would I
be able to hear it - many things make measurable differences, but are
they audible......

The difficulty is that the question is unanswerable without more
information. :-)

From what you have reported thus far, I suspect that any differences will
be between 'minor' and 'inaudible'.... but you may be able to correct this
in the light of experiment. :-)

Slainte,

Jim

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