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14th April 2009, 04:06 AM  #1 
diyAudio Member

Calculations for MC Transformer
OK, I am unable to figure out/find how to calculate the step up required for an MC transformer.
I'm looking at purchasing a pair of Lundahl MC transformers. I've narrowed it down to the 9206 which is 1:5, 1:10, and 1:20 and the 1678 which is 1:8, 1:16, and 1:32. What I have is an Aikido phono pre using 12AX7s in the 2 gain stages. The 12AX7's have a gain of 100 and in the Aikido it's equal to roughly 1/2 of that. So between the 2 stages i'll have roughly a gain of 100. The output is the regular unbalanced, but i was thinking of using a 5402 in 1:1 on the output to balance it. It needs to have enough signal to push a 600 ohm +4 input. The cartridge that will be used is a Denon DL103 with an output of .53mV. What transformer would be best? How would you be able to figure this out and also how do you determine how much gain from the turns ratio? Any help is appreciated. 
14th April 2009, 04:07 AM  #2 
diyAudio Member

Sorry, the output of the Denon cartridge is actually .3mV, not .53mV as previously posted.

22nd April 2009, 08:14 AM  #3 
diyAudio Moderator Emeritus
Join Date: Jan 2003
Location: Near London. UK

Rule of thumb is to avoid ratios > 10:1.
I don't think the DL103 will like a transformer because it has a high source resistance, which will combine with the leakage inductance of the transformer to give a rolledoff treble. I suspect this is one of the reasons for the strongly polarized opinions on the cartridge  some people had no transformer, others good transformers, and others poor transformers. Thirdly, few transformers will like feeding the high input capacitance of ECC83. Another reason to stick to < 10:1.
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