Here is the scenario:
Passive I/V stage (2K7 to ground) --> 4.7uF coupling cap --> 12H log tapped autotransformer (100 ohms DCR) as volume control --> 22K input impedance at amplifier.
I figured on some easily measurable (and possibly audible) LF roll-off due to:
1) lower AC impedance to ground at LF for the I/V stage
2) voltage divider effect of the cap + autotransformer at LF
Tried it - couldn't hear any roll-off. Measured it (with CRO) - I get 1 or 2db down at 10Hz. No humps, bumps or dips from 20Hz to 20kHz.
It could be that I don't fully understand how the passive I to V works from the DAC, but I'd guess that the DAC's current output causes a voltage to develop across the resistor to ground.
I guess the other possibility is that the autotransformer is much more than 12H, but I don't think so. That figure came from the maker.
Any thoughts on what I'm missing?
Passive I/V stage (2K7 to ground) --> 4.7uF coupling cap --> 12H log tapped autotransformer (100 ohms DCR) as volume control --> 22K input impedance at amplifier.
I figured on some easily measurable (and possibly audible) LF roll-off due to:
1) lower AC impedance to ground at LF for the I/V stage
2) voltage divider effect of the cap + autotransformer at LF
Tried it - couldn't hear any roll-off. Measured it (with CRO) - I get 1 or 2db down at 10Hz. No humps, bumps or dips from 20Hz to 20kHz.
It could be that I don't fully understand how the passive I to V works from the DAC, but I'd guess that the DAC's current output causes a voltage to develop across the resistor to ground.
I guess the other possibility is that the autotransformer is much more than 12H, but I don't think so. That figure came from the maker.
Any thoughts on what I'm missing?