I've bounced around in the Oade forum to try to find a definitive answer, to no avail. Confusing discussions around whether the stock SBM-1 uses:
- a 20-bit converter and utilizes super bit mapping quanization to achieve 24-bit quality before dithering down to 16-bits, or
- a 24-bit converter which utilizes super bit mapping quantization to achieve 20-bit quality while/after dithering down to 16-bits
Doug doesn't mention modifying the converter chip in his description of the mod, nor have I seen it mentioned *anywhere*. As such, I assume Doug doesn't appear to modify the ADC chip. If he does, his description of the mod is incomplete:
"The fourth [mod] is a complete line stage rebuild which dramatically improves the sense of depth and detail in the SBM-1."
As I understand it, this is strictly an analog upgrade to improve the analog signal being delivered to the chip prior to A > D conversion. Hence, the description "24-bit mod" IMO is misleading/incorrect b/c regardless of which situation applies above, the ADC itself - and therefore the bit-depth of the device - is NOT modified.
At least that's my understanding.