Jim Audiomisc
pfm Member
I've just encountered an old myth which has poped up again in a new guise. The (false) claim is to the effect that MC carts "produce NO noise" whereas MM types do.
The official classification academics employ for such a claim is "bollox"
The physical reality is that *all* resistances generate thermal noise. And the power of this noise you get is determined simply by the bandwidth examined and the temperature. So MC carts *do* generate the same amount of noise power as MMs from this physical process. (OK, if someone has made a cart that is a superconductor I've missed that.)
When this myth cropped up a few years ago I looked at measurements on a random sample of carts and plotted this:
http://jcgl.orpheusweb.co.uk/temp/MMvsMC.png
This plots the details of the MM and MCs as measured.
The way to maximise *signal* output (if that is your only concern) is to 'match' the source impedance to the load (amp input) impedance. This is why people use a 'step up' transformer.) If I did that for the MCs you get the boosted signal *voltages* as shown on the left. BUT this also 'transforms' the noise *voltage* from the MC, so doesn't ensure you improve the ratio.
To get optimum signal/noise you also need to take other amp details into account.
If you consider the ratio set by the sensitivity and resistance of the cart you get the plot shown on the right. This shows how many examples of a cart type give a particular max possible signal/self-noise ratio.
Note that unlike the myth. None of the MCs show no noise at all. Many show poorer ratios than MM.
So avoid falling for the mythstake that has been repeated.
The official classification academics employ for such a claim is "bollox"
The physical reality is that *all* resistances generate thermal noise. And the power of this noise you get is determined simply by the bandwidth examined and the temperature. So MC carts *do* generate the same amount of noise power as MMs from this physical process. (OK, if someone has made a cart that is a superconductor I've missed that.)
When this myth cropped up a few years ago I looked at measurements on a random sample of carts and plotted this:
http://jcgl.orpheusweb.co.uk/temp/MMvsMC.png
This plots the details of the MM and MCs as measured.
The way to maximise *signal* output (if that is your only concern) is to 'match' the source impedance to the load (amp input) impedance. This is why people use a 'step up' transformer.) If I did that for the MCs you get the boosted signal *voltages* as shown on the left. BUT this also 'transforms' the noise *voltage* from the MC, so doesn't ensure you improve the ratio.
To get optimum signal/noise you also need to take other amp details into account.
If you consider the ratio set by the sensitivity and resistance of the cart you get the plot shown on the right. This shows how many examples of a cart type give a particular max possible signal/self-noise ratio.
Note that unlike the myth. None of the MCs show no noise at all. Many show poorer ratios than MM.
So avoid falling for the mythstake that has been repeated.