My comparison was a stock Mojo2 vs a Dave modified with a Sean Jacobs DC3 and capacitor board. I applied all my experience and kit to make each DAC sound its best ...and enjoyed several listening sessions with many types of music.
As per the schematic drawing, input was Dual BNC/Coax from a Windows 11 laptop with foobar and exclusively PGGB 256 content. Output was RCA to a headphone amp (Accustics Arts Preamp-II Mk2) to HIFIMAN HE1000se. I applied RF-STOP filtering to the max using my new EXTREME filters as well as DAC-WRAP magnetic shielding. Of course, everything was on batteries for sound quality and to avoid AC mains for comparison fairness.
The Verdict...
No contest! Mojo2 is more transparent than Dave - markedly so! Dave is certainly very smooth and reveals all details but Mojo2 is plainly superior. Dave obviously has connectivity and features to fulfil its role as a flagship DAC, however, with the above setup and the specific goal of 'reality creation' the Mojo2 is clearly better. The reasons? Well, let me offer my informed speculation:
1. External upsampling. PGGB 256 sound quality is so compelling that it outweighs the encumbrance of required pre-processing. Ordinary CD FLAC upsampled to 16fS@24bits bypasses the Chord WTA1 filtering to reduce FPGA clocking/noise and moots any tap count advantage. PGGB 256 sounded stunningly good on Mojo2 - showing that Rob's latest and greatest FPGA may be superior to Dave's dated 2015 design. Also, the Mojo2's higher internal precision likely played a role.
2. Battery power and filtering. Avoiding AC mains wideband RF noise for this comparison meant Dave+SJ ran on AC from my chosen Analytic Systems low noise inverter. Battery BMS (battery management system) and inverter generated RF noise was filtered using my latest RF-STOP products. IMO, this made the Dave+SJ stack sound its best yet Mojo2, with its internal battery power, won out! So lower power D/A conversion circuits results in less internal noise and more transparency. Kudos to Mojo2's excellent battery powered design.
3. Optical signal isolation. OPTO-DX plus DC-BLOCK and LP-FILTER is my offering as the best input to a Chord DAC. The optical RF noise isolation avoids the need for a dedicated low noise source and avoiding USB is always a good thing. Extreme filtering of DC power for OPTO-DX ensures the lowest noise galvanic DBNC connection. IMO this equated Mojo2 and Dave input quality despite any additional Dave input filtering.
4. Filtered RCA Output. The output stage design of both Dave and Mojo2 has protection against downstream RF noise making it back into the DAC. Arguably Dave may have a better implementation. To block this RF noise I applied my recently introduced RF-STOP EXTREME Signal Filter. This uses lossless skin effect filtering so any difference in Mojo2 and Dave output ingress was minimized.
5. Line Level Output. Both DACs used only line level output to a high impedance external amplifier. Since line level requires only voltage sensing this means that electrical current demands are negligible. This equated Dave's lower distortion headphone amp (with all its high cost/quality components) with Mojo2's more economical implementation.
6. Radiated Magnetic Noise Shielding. The influence of household electronics induces magnetic fields which induces electrical current in circuit traces. The frequency is sympathetic and typically in the high MHz (SMPS, computers, switches). DAC-WRAP was applied on Mojo2 and Dave to yield the most transparency from each.
7. Mojo2's 104bit Precision vs Dave's 64bit Although the input of a PGGB 256 16fS bitstream bypassed the WTA1 filter, the higher precision of Mojo2 benefited the transparency of the noise shaper and final stages of processing. This allowed more of the inherent resolution of PGGB to be revealed.
In summary this comparison favored Mojo2's newer design. PGGB 256 was the DAC, per-se, and all that was being asked of the hardware was input and output to be as clean as possible. I have become so enamored with this result that my next blog will detail everything you need - batteries, cables, my kit, costs, etc. to obtain this same Mojo2 endgame.
For many this comparison is impractical and academic as the DACs are different products. Perhaps but there is no arguing that, the Mojo2 setup for a fraction of the cost of a Dave setup, can get you a much more transparent sound.