MC LOADING & STEP UP DEVICE

Step 1: Find out the winding ratio of the trannie.
e.g. 20dB = 1:10; 26dB = 1:20; 30db = 1:31.6; etc.
(there are more on the web, no need to calculate...)

Step 2: Find out the 'natural impedance' of the trannie.
Ratio^2 * phono-pre input impedance
e.g. 31.6 * 31.6 * 47k ohm = 47 ohm for a 30dB trannie
(this will be what the cart sees if you do not use secondary or primary loading of the trannie)

Step 3: Check for phono-pre over load
e.g. of cart V = 0.25mV; cart DCR = 6 ohm
[cart output V * ratio]* [load impedance/(load imp + cart DCR)] =
e.g. [0.25 * 31.6] * [47 / (47+6)] = 7.9mV * 0.887 = 7.0mV

try for max. input value not to exceed ~ 7.5mV

With a 26dB, you will have a higher 'natural impedance' i.e. 117.5 ohm (and not 47 ohm as with a 30 dB item) which in turn might require secondary or primary loading to lower the impedance that the cart will see.

Secondary trannie loading is reflected 'back' to primary, by dividing the secondary R by the square of the winding ratio.
But first you have to get the correct value e.g. if 18k ohm is loaded on the secondary then:
47k*18k / 47k+18k = 13.01k ----
then reflected = 13.01k / 31.6*31.6 = 13ohm that the cart will now see.

But secondary loading will ALSO have the effect of damping the trannie, as more current is pulled on the secondary side, this may be just what is needed -- but it may be also not a good thing --- only testing & listening will tell.

If primary loading is indicated (if e.g. secondary gets too dull) then:
e.g. 18ohm load R with 47ohm 'natural impedance' =
47*18 / 47+18 = 13 ohm again what the cart sees.

I hope this will be enough to give you a starting point for checking the various option.
Cheers,

Al, thank you for clarifying this:
>> In Axel's example, the 18K that he assumed was in parallel with the 47K preamp impedance represented an external 18K resistor, not the transformer's secondary coil impedance.<<<

The example aught to be clear, by looking at the basic calculation of parallel resistance: 47k input impedance parallel with an 18k load resistor on secondary.

It true, that the secondary coil DCR is ALSO reflected back into primary, again by dividing it by the square of the winding ratio.
B U T, it would be negligible in the case of my example and would be about 0.06ohm added to the calculated 13ohm of the example.
In the case of an FR XF-1 type M, (30dB) primary DCR = ~1.6 ohm, and secondary = ~ 60ohm (if I recall it correctly).

Sorry for the silly typo!!!!!
It must read of course:
47k ohm / 31.6 * 31.6 = 47 ohm, for a 30dB trannie

Hi Al,
I think you do make the better teacher then I feel myself, as you have it so well explained.
Let's see if this gets Dfelkai sufficient clarity to proceed.
Thanks again, and let's see what comes up next.