"By pressing the input button then rotating the volume knob, the gain level in the menu can be adjusted in 0.5dB steps. With gain set to the max +24dB and the volume knob/attenuator to 0dB, the voltage at the amplified outputs swings ±17V or 34V peak to peak. With both gain and attenuation at 0dB, the same output swings ±2V or 4Vpp. This range of adjustments should drive any headphone or power amp direct, even amplifiers with very low input sensitivity and/or very low input impedance. When driving a preamplifier, the amplified outputs can be set to below 10dB and customers have declared this to be the configuration. With the DAC-direct outputs, the same settings correspond to ±2V and ±0.125V.

"In the menu, the visible parameters to adjust are

balance                                  range from 5.B left to 5dB right in steps of 0.5dB
phase                                     absolute vs. inverted absolute polarity
LCD brightness                      display brightness 50% / 60% / 70% / 90% / 100%
LCD dimmer                          display dimmer timer 10s / 20s / 30s / 40s / 50s / always on
sample rate                           show/hide (in large digits for 5 seconds)

In the menu, the invisible parameters to adjust are

oversampling filter                on/off                                                                         (default ON)
jitter filter                              on/off                                                                         (default (ON)
FIR filter                               USB i²S only: sharp filter / smooth filter                     (default ON)
IIR filter                                USB DSD only: maximum / medium / minimum        (default MEDIUM)
DAC resolution                    6 bits, 7 bits, 8 bits, 9 bits (Sigma Delta)                   (default 8 bits true differential)

"When I introduced the ZeroUno DAC, I received too many emails about the meaning of each parameter, how it influences the sound and when it should be used. So I decided to hide them. But if you press the setup button for at least 30 seconds, you can access them again. Should you lose control over the unit, keep the setup button pressed for at least 10 seconds but less than 30. Now the firmware resets to factory default. This information is not in the owner's manual. By request and for free, the firmware can even set the DPLL mode, bandwidth and phase, a notch filter and the input format (how many bits, left or right-margin justified) but those parameters only I can access. To the end user they're blocked. Since I developed this firmware, I can in fact implement any custom configuration at the cost of my development. The same goes for MQA where I developed and designed the USB transceiver and its firmware. I can custom tailor this firmware to a customer's needs as long as I don't violate the NDA I signed with MQA London. With the firmware inside the Sabre32 chip being comploetely mine, I can do whatever I want, not because I'm a dictator but because this has been my job for 35 years."

As we learnt, the ZeroUno is an unusually flexible DAC. It can be set to the same 2Vpp for its direct and amplified outputs. That gives customers the option to insert an output buffer without altering gain. Should more gain be desirable, the active outputs can scale up to 34Vpp. That flexible gain coupled to 32-bit digital attenuation really ought to cover all eventualities including very long cables. The only questions I still had were when one may want to deactivate the jitter filter; and why Mario hadn't transitioned to the ESS 9038Pro.

"The Sabre32 implements a patented jitter reduction algorithm to strip from the incoming signal any super-imposed jitter. With CD playback in particular, this jitter reduction is extremely effective. If you stream through software like Foobar, Audirvana, PureMusic or J.River, they already apply their own jitter suppression. Once you stream a digital master file, you may have hardly any jitter at all. Jitter reduction uses more CPU resources inside the Sabre chip. Turning off the algorithm lowers the load. That said, the throughput with the clock at 100MHz is high enough to let the algorithm run constantly and still have more than 50% headroom. The jitter correction algorithms of today do not work like the error correction did in the mythical Philips TDA1540. We are 30 years ahead of that technology.

"About my chosen DAC chip, any D/A converter is based on its chip (or discrete equivalent) and its physical implementation, firmware, output stage and power supply. In the ZeroUno family there are 14 discrete power supplies all executed around AD797 operational amplifiers which are usually seen in high-quality output stages. On today's market, you can easily find ES9018 DACs from €150 on eBay or AliExpress to over €50'000 on the High Street. Obviously they don't remotely sound the same. The key differences are the power supplies, output stages and how you filter the signal at the output of the SigmaDelta converter.

"If I changed from the 9018S to the 9038Pro, the final result at the ear wouldn't change with the same power supplies, output stage and filter section. If we measured it, the newer chip would show a better S/NR. But whether your noise floor is -125dB or -135dB down makes no difference to the ear, only to a 100MHz oscilloscope. And the ES9038Pro implements MQA decoding whereas I prefer my own implementation on my USB board where I'm free to tailor the firmware. And whilst the ES9038Pro is shielded to improve its predecessor's known EMI susceptibility, I prefer my own implementation with a dedicated shielding technique that's now very difficult to beat." Straight talk from a no-nonsense engineer. To wrap up, the ZeroUno stable demands from €7'550 for the straight-ahead DAC to €9'550 for the Plus version with analog inputs and analog volume. At €4'560, the HPA uses the exact same converter stage, eliminates the tubes then adds headphones. Within this portfolio, it may be the entry-level machine but its engineering approach and purist execution are exactly the same as all the others.

About finish options, "standard is anthracite, a metalized dark grey. Distributors can get any RAL color at the specified gloss level with a minimum order of 4 pieces, otherwise production costs are too high. End users also can order special colors but lead times increase and there will be a one-up surcharge." Shipping from Italy's Treviso to Ireland's Shannon airport with same-day delivery took 3 days.