Velocity is not Amplitude - Pick Up Cartridges

For all those people who have said in the past, are saying now, and will say in the future: "the output of a magnetic phono cartridge is flat" go and write on the blackboard 100 times ...

Velocity is not Amplitude

Magnetic cartridges called a constant velocity device do not produce a flat amplitude output.

Their output is proportional to velocity (you can call it speed to make it easier to understand).

Bass frequencies rise slowly - the velocity is low - not very fast. The electrical output will be small.

Treble frequencies rise fast - the velocity is high - very fast. The electrical output will be high.

So if we take a frequency response plot of frequency versus amplitude what will be its shape?

Not flat!

It is a rising slope - left side low - right side high - with an incline of 45 degrees.

That isn't flat.

This is why a phono preamp with EQ (equalisation) is necessary which folds the plot down at 45 degrees to make it flat.

When that is done you will find the output from a record isn't flat either.

The response kicks up to the left at 50Hz, is flat to 500 Hz, kicks down to 2122Hz, and is flat from there to wherever the mastering suite decided to "cut off".

So inside the phono preamp there is additional circuitry to correct that too.

Got it?



Edited by Graham Slee - 25 Jul 2016 at 6:37am

Has someone incurred a 'whole can of woop ass' ?