SDA-3 the next step. "Work on the SDA-3 already indicated that at low levels, distortion would be 3 x lower. With the knowledge that to be on the safe side, fast circuits are sensitive to layout, all the knowledge gained with the pots transferred to a modified SDA-2 using fixed components. The differences now are much shorter connections over the prototype with pots. Because the SDA-3 creates about 13 volts out, more mods are required. The I/V section of the proto turned out to not only have lower distortion at low levels but when properly loaded by a low-impedance voltage divider, a factor of 3 x lower distortion also at full output. It appears that even the relatively short traces to the pots applied in the SDA-3 proto had a poor effect on performance at high levels. A Morpheus with two SDA-2 modules had 0.0035% distortion, the SDA-3 placed in a modified Morpheus 0.0015%. This still is no production Morpheus but similar to the proto motherboard with 2 modules per channel operating at high supply voltages and using a 30VA transformer. From this we can conclude the following:

1. Relatively long traces are counterproductive and already indicate just how important the I/V section is.
2. The correct load and attenuation characteristics of the module are very important for obtaining low distortion and at the same time ensure the correct output voltage of 4V on XLR and 2V on RCA.
3. For Morpheus running the SDA-3, a 33Ω¹ direct-coupled output impedance is already achievable. In the case of Father of Morpheus with eight modules, this will probably halve again.
4. This creates the very real possibility of matching a very wide range of power amplifiers regardless of their input sensitivity by using programmable attenuators and keeping the extremely low output impedance plus very low noise figures.
5. What we have also seen already is that both the 2nd and 3rd harmonic distortion is about the same regardless of signal level.

Time to implement this knowledge in the final design!"

¹ Keen observers of DACs whose resistor ladders direct-couple to the outputs without a buffer will know that Denafrips converters for example show 625Ω and 1'250Ω output impedance on RCA and XLR respectively. Cees works significantly lower.

"We recently delivered three custom Morpheus to the Record Company in Haarlem. They're offered masters from very prestigious labels to put on vinyl. What transpired is that 0dB is not the maximum output applied to a DAC but the ceiling is 14dB lower. This is also my experience. Well-recorded music leaves a lot of room relative to the most significant bit. So this graph at -14dB is perhaps even more important and shows 0.001% distortion with the second and third harmonic in balance."

By mid October, word had gotten out about the final name—Pasithea so actually, the mother of Morpheus—and a first public showing during the Dutch hifi show. That concludes our tech intro to continue with the formal but separate Pasithea review.