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Cartridge Loading into Step-Up Transformer

I have read a lot about preamps and phono stages having the ability to put a load resistor in parallel to the cartridge.  Some products have flip switches, others have solderable terminals inside the unit to put in a custom valued resistor and others have a pair of external RCA jacks to put a resistor here.  Mt preamp has the latter.  However, if an external  setup transformer is used into a MM input, what is typically done to accommodate a load resistor?  Is the resistor in parallel with the primary or the secondary?  And is the resistance value typically different for a given cartridge that worked well into an active MC stage vs. a setup?  Any experiences, ideas, suggestions, etc., would be greatly appreciated.
John
jafox
noromance's avatar
noromance
9,404 posts
 
No need for a resistor. The SUT input impedance should be 10 times the internal resistance of the MC coils. You'll need to calculate the SUT turns ratio for the given MC output level.
The SUT plugs into the standard 47k MM input of the phono amp.
chakster's avatar
chakster
6,144 posts
 
Most of the SUTs has written value near the input RCA, so you can go wrong with cartridge you can or can’t connect to this particular SUT.

For example: 3 Ohms, 10 Ohms, 40 Ohms.

If your MC cartridge impedance is 2-3 Ohm then you need a SUT with 3 Ohms value written just near the input RCA and so on. Pretty easy.

The SUT itself is always connected to MM (47k Ohm) input of your phono stage.
folkfreak's avatar
folkfreak
1,349 posts
 
This is a pretty complex and tendentious subject. See for example
http://www.rothwellaudioproducts.co.uk/html/mc_step-up_transformers_explai.html
http://www.6moons.com/audioreviews/stepup/primer.html

best advice is to work with who ever designed your step up to ensure it matches your cartridge. Some step ups (such as the MFA I use) do actually offer variable “loading” so you can fine tune the response to suit the cartridge and recording but simply adding a resistor in parallel to the transformer can cause problems such as ringing so stick with the methods the step up maker designed 
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