Does anyone else have a TF2-30? What are the specs on your cart and is it happy with the impedance?
I read that input impedence is fixed on all TF2 at a very high 47k!
The user manual is misleading
so I'm editing my post for the record, based on some info from Bryston and the datasheet for the Jensen transformer inside the TF-2.
The TF2 is like most any other transformer and has a "natural impedance" which is a factor of the turns ratio
. The 47k ohms comes from the MM stage it is most likely connected to. The formula to calculate the input impedance that a cartridge would "see" is:
Zin = 47,000 ohms * (Turns_Ratio) ^ 2
where the TF2-20 Turns_Ratio is 1:10.
Zin = 47,000 * (0.1) ^ 2 = 47,000 / 100 = 470 ohms
The TF2-30 turns ratio is much higher (probably 1:35) so its Zin will be lower (< 40 ohms) as expected. This is probably more important for cartridge matching than the actual voltage gain in dB.
Here's more info on the theory and a table of data on step-up devices:http://www.mh-audio.nl/StepUp%20Transformer.asp