I just recapped and put into service an old Micromega Trio DAC (the CD unit is dead). This machine uses a 1bit, 256X oversampling, PDM Philips DA chip. Ted, is the architecture of this machine the same as the DS DAC except for the lower 11.29 MHz sampling rate and different filters? The build quality is quite nice utilizing a solid aluminum case which is hallowed out, a separate power supply with five transformers and discrete regulators in the DA chassis.
I don’t know the exact D/A used in the Micromega Trio. I think it was an early Philips sigma delta DAC. In the abstract they do convert CDs to a single bit bit stream and then analog filter it. Because the filtering is done on the single DAC chip it can’t use precise valued components so they use dynamic element matching to use multiple units randomly to smooth out the manufacturing differences between them. This is a great technique if you are designing a single chip D/A and it’s used in most all sigma delta DACs today.
The early sigma delta chips are closer in some ways to what I’m doing than current sigma delta D/As, but in other ways I and current chips use higher order sigma delta modulators than the early chips so I’m hard pressed to say which pairs of the three are most similar.
Here’s a Stereophile article about the early Philips sigma delta chips: http://www.stereophile.com/content/pdm-pwm-delta-sigma-1-bit-dacs-john-atkinson
Thanks Ted. The Trio uses two SAA7321 chips (one per channel) in a differential configuration. Compared to my DS DAC bass is a little looser and less extended, the highs are less detailed and dynamics are a little compressed. That being said, the sound is liquid smooth and appears to come from behind the speakers with good imaging and separation. Poor recordings actually sound better than on DS, however, the DS is superior on good ones. Playback is limited to a maximum of 48 KHz sampled files.