I just got two pairs of fresh Duracell 9-volts and put them in the amp and DAC (even though the DAC pretty clearly isn't the problem). With my (old) K240Ms, the problem is greatly minimized, but with my (new) K701s, it's only a little better.
If it helps at all, this problem mostly surfaces in recordings of one-to-a-part performances of Renaissance choral music, in passages where the soprano is singing high in her range. My collection is a mix of MP3s and AACs ripped at 128, 192, and 256kbps (mostly 192 kbps), and I'm using iTunes on my MacBook Pro, connected to the Micro DAC with the optical out.
Anyhow, I have another pair of power supplies on order, and once I get them, I won't be using batteries at all, really, so it's not a big deal. I mostly got the MicroStack so I could have something transportable to bring between home and the office---my limited portable needs are still covered by my iPhone and Shure SE210s.
Thanks,
David
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