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RE: AD1955 and transformer I/V stage

Posted by SunRa (A) on June 10, 2007 at 05:04:47

In Reply to: RE: AD1955 and transformer I/V stage posted by Dave Davenport on June 9, 2007 at 15:27:15:

Hello Mr. Davenport,

Well I re-read my post above and I realise it was wrong, mostly regarding the impendance ratios. I was thinking more in the terms you described.

It's hard to find some good literature about interstage transformers so I try to learn mostly from forums like this. I read the aplication guide for the MC cartdrige and the LL9206, although that example works on voltage output rather than current.

I'd like to properly understand the reflected impendance at the DAC output (without considering the primary's resistance this time; this of course will add to the final impendance). More, I'm not intersted at this moment of a volume control, so the aditional circuit is not taken in consideration.

Now, with a ratio of 1:10, the current at the secondary will be arround 0.86mA (considering the 8.64mA output of the AD1955) is this correct? This is the current that will be converted by the two input resistors that in your output stage have 75 ohms each? And from here, I have to figure out the gain I need from the tubes for a 4V output. Now, asuming that I know the load on the secondary of the trasformer (which at this point I don't know how to calculate it) , the impendance reflected at primary of the transformer will be this load diveded by 10 or multiplied by 10? Because the ratio is 1:10, I'd say the reflected impendance will be load*10. Of course, adding a resistor across the secondary, will decrease this impendance, but will affect the gain too.

I hope I'm not boring too much, only that it's hard for me to find some good learning material regarding these things.

Florin

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