Mojo2 has been winning awards and accolades since its launch. At a street price of $500, it is a hi-fi bargain that has allowed the audiophile masses to experience a taste of 'transparency': that strong sense of reality creation which, IMO, is essential for full enjoyment of music. For over 10 years I have been at the forefront of understanding how to improve a DACs transparency through isolation of RF noise. In that pursuit, several brands of DACs have crossed my desk but those from Chord Electronics, IMO are without peer. I've owned 2Qute, Hugo2, Qutest, TT2 & Dave and most recently, the very special Mojo2. It is the DAC I have chosen to be integral to my reference system (REFERENCE Mojo2).
It is possible to bump up DAC transparency through ad-hoc application of point product fixes (like cables, power supplies, USB filters, etc.) but this approach can be frustratingly unsatisfying as results can vary with too many variables and individual situations. So my decision was to focus on a single DAC. Some may doubt how it's possible that Mojo2 (being a mobile entry class design) can compare at the highest level but the fact is that all Rob Watts designs are FPGA firmware based and Mojo2 has the latest version. So, at it's heart, Mojo2 is basically a 'son-of-Dave' with 10 years of firmware updates and improvements plus a higher precision DSP and an updated analog stage. Transforming it to reference level transparency required a singular approach: fine tune the hardware and select the absolute best signal and power.
To start, I needed to open the Mojo2 using a Torx T-6 to remove the 8 screws (check out YouTube videos and forum posts). Note that this will void your warranty so there is no going back. Then refer to the diagram below and my description of what I did and why.
- DISCONNECT BATTERY. Without a battery connected, Mojo2 switches to using external 5V power (Desktop Mode) immediately - a process that otherwise takes several minutes until the battery is 100% charged. Additionally, with no battery, Mojo2's microcontroller will not need to perform LiFeP04 battery cell monitoring - a potential source of RF noise. To remove the battery terminal connector, just tug on it gently or lift it with a precision flat screwdriver. Tuck away the connector with a shield of insulating tape (or you can just remove the battery entirely).
- DBNC INPUT and USB N/C. DBNC (Dual coax) is Chord's native input and directly decoded by the FPGA. When Mojo2 detects DBNC INPUT and no connected USB inputs it disables the USB Interface chip and this turns off RF noisy USB clocks and processing. Use SRC•DX to provide DBNC as the transparency benefit is substantial.
- BYPASS FPGA UPSAMPLING. Mojo2's hardware upsampling (WTA1 filter) requires intense FPGA processing which generates RF noise. Using software upsampling like PGGB avoids this: DBNC input of 24bits@16fS bypasses the WTA1 filter so the FPGA performs only lightweight interpolation to the final analog rate.
- 5V DC POWER. The Mojo2 battery is outstanding - yet it can be bested by an external power supply with better specs. My PURE-DC product, based on a supercapacitor design, has near zero noise and near zero ESR (equivalent series resistance) plus relay-based AC mains isolation. This allows Mojo2 to render the final D/A stage (bits-to-volts) with unbelievable levels of transparency. Additionally, PURE-DC has such low ESR (0.23mOhm) that it acts as a sink to RF noise on the ground and reference voltage planes.
- LOW OUTPUT IMPEDANCE. Mojo2 analog outputs have an incredibly low 0.06 ohms impedance. This means that output current draw (into high impedance inputs of a preamplifier) has negligible resistive loading. Mojo2 captures all the resolution of the digital signal into the analog waveform.
- SELECT LINE LEVEL VOLUME. As configured for my reference system, Mojo2 is in fixed volume mode to allow for a Faraday RF isolated hands-off situation with downstream analog volume control. Choose a line level of 3.0v or 4.3v to maximize Mojo2's dynamic range and to best suit the needs of your preamplifier.
- TURN OFF CROSSFEED & EQ. Mojo2 has a 104bit DSP to handle all internal signal processing. With regard to cross-feed and EQ, the algorithms and processing may be lossless and beneficial to frequency response but my rationale is to turn off cross-feed and EQ since that avoids RF noise and the potential negative effects on transparency.
In my next blog post I will describe the Mojo2 chain inside my RF•STOP Faraday Isolation Box.