line level strength - big boost required

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I've recently reduced the IV resistors on my AD1865 DAC to 10R, as I noticed that dropping the value (from 500R, to 22R, then to 100R, then 50R, etc) gave an increasingly more well defined and 'organised' sound.

However, the catch now, is that the line level is so low that even my preamplifier with 15dB gain is not delivering enough of a signal to drive my Push Pull power amp.

The AD1865 puts out 1mA only, so if I/V resistor is 10ohms, then; 0.001 x 10 = 0.01V. This is more like an RIAA or instrument level strength!

How many dB gain would be required to get this level to something more like 750mVrms or 1vrms (roughly the input sensitivity of most power amps these days)?
 
I found a pair of linestage output transformers which I had from a previous project:
St 20600 OB Audio Transformer 20? 600? for DAC | eBay

Specs as follows:

1. 20 Ω : 600 Ω (CT 150Ω) 1:5.48(2.74)
2. Distortion (THD) : <0.001% @1KHz
3. Frequency Response : 5 ~ 100KHz(-3db)
4. Power Level : MAX +24dBu @20Hz

So, with a 10R iv resistor I have:

- 0.001 x 10 = 0.01V (10ohms)
- 0.02V x 5.48 = 0.055V (600ohms output impedance)

the output voltage of transformer is about 0.055V at 600ohms

this output impedance is low enough to use with nearly any linestage or preamp

So, based on:
20log(1/0.055), we see the required voltage gain to get the level to drive a typical power amp is about 25dB. Still quite a lot of gain.

What type of circuit would implement this kind of gain in the most linear fashion?
 
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