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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
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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jafox OP
1,447 posts
 
Thank you very much for the input here.  The pasted links above provide for much education on the handling of the required gain and ultimately the loading.  I read this material several times to understand the subtleties. 

I just bought to Hashimoto HMU-7 SU transformers to use with a newly diamond re-tipped AQ 7000 which has one of the lowest coil resistances at 2 ohms.  And I will look to use both the 1:15 and 1:30 options of this SU.

Using the rule that the input impedance of component B (the SU transformer) must be at least 10x the output impedance of component A (the cartridge), I have just done the math to determine the starting points for some load resistors in parallel with the 47k MM input and compare with none here at all.  Then I can tune by ear to get the optimal.  This will be fun.

Thank you again.
chakster's avatar
chakster
6,144 posts
 
I just bought to Hashimoto HMU-7 SU transformers to use with a newly diamond re-tipped AQ 7000 which has one of the lowest coil resistances at 2 ohms.

99% of my LOMC cartridges are about 2 Ohms too.
This is one of my SUTs: Luxman toroidal silver SUT
I can swap the SUT in the base, as you can see there is a recommendation for use a cartridge with certain coil impedance (under 3 Ohm is one SUT, there is another for about 40 ohms).

So it's not necessary to count 1:10 , 1:15, 1:30 or whatever ... just looks at the recommended connection impedance printed on the SUT input and choose the SUT for your cartridge self impedance accordingly


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