D1 I/V volume control

[poolorpond]

I have spent hours reading posts about volume control. However, I have not seen anything about this idea in particular (applied to the D1). Rather than use pots at the input or output, I would like to change the gain of the entire circuit (or four independent circuits, depending how you see it) using one stereo pot, using one deck for the left and one for the right. This way I will not have to deal with tracking between +/- only l/r. I also don't need another gain stage or I would just build the BLS, using its coupling resistor.

The idea is, of course, not novel. Nelson writes in his paper on the balanced zen linestage that the gain of the circuit is determined by the ratio of the ouput impedance to the resistance of the coupling circuit. On the pic below, this would be the 124R resistor in the middle.




I don't really know how this coupling resistor works well enough to apply it to the D1 I/V stage. In particular, assuming I can calculate the right ratio, where should it go? My thought is that it should go just above R2 or R4. But I really have no idea. Oh, this is 1/2 of the balanced D1.



Yes, I'm sure that I could "just build it and see" for myself. But, that would not not help me understand why. Also, I'd prefer not to kill the DIY DAC (ak4524) by shorting something or pulling too much current. It sounds so good with my aleph 5 clone so I would hate not to ask first. An entirely balanced system from dac to amp is awsome.

Any thoughts?