(Updated October 5, 2020)
This is my take on a proposed endgame system for DX compatible DACs driving amplified speakers. It uses my full gamut of RF isolation kit and I'm still evolving it to provide uncompromising sound quality at the lowest cost. Yes there are batteries (Goal Zero) as I cannot find an AC mains connected solution that preserves the same transparency I hear with batteries.
① Signal From Source to DAC
I use OPTO-DX to optically modulate a high resolution PCM signal from an HQPlayer source via SRC-DX through an RF-STOP Isolation Box. OPTO-DX connects to the DAC via dual SPDIF connections using 75Ω digital audio grade coax. You want coax with as high a screening factor (internal/external RF attenuation) as possible. Coax cable with high screening is more rigid and sometimes impractical but always preferred. I suggest Belden 1694A for both its good screening and flexibility although I'm always on the lookout for something better. Note that there is no additional benefit of using clip-on ferrites over highly shielded coax. IMO, its best to solve conducted RF issues with cleaner power (see ③ below).
② Analog Output Signal from DAC to Amplifier
Analog outputs from my DACs are either balanced XLR or RCA but I use XLR as it sounds equally transparent to RCA and compatible with my pro-audio speakers. Regarding choice of interconnect cable, I will go on record to say that the only technical aspect that matters is RF shielding to reduce the antenna effect. Copper gauge, metallurgy or connector are superfluous considerations unless you know they provide significant benefit to reducing RF absorption/transmission. I've grown very fond of Gotham Audio 10561 GAC-2 UltraPro cable due to its triple shielding and affordability. Recently, I have found that adding my RF-STOP Cable Sleeve to the interconnects provides further shielding and reveals even more transparency.
③ DC Power to DAC and OPTO-DX
For DACs that support a DC input, the galvanic connection of the DC power input still allows power supply and RF noise to affect the sound. I have tried to minimize the extremes required but my suggestion is you need batteries or a highly regulated DC supply (Farad Super3). Even then I suggest a high attenuation RF filter from Schaffner. In the case of power for OPTO-DX, the fact that both it and the DAC can run on 12v-15v allows them to share the same DC power. This may also have the advantage of sharing a signal and power ground.
④ AC Power to DAC
With any AC powered DAC, having ultra low noise power is vitally important. In my system I combine my RF Filtered power cord and RF-STOP Cable Sleeve with a battery. So I have no AC mains noise and no impact of radiated RF noise.
⑤ Amplifier AC Power
Amplifiers don't need better power cords to sound better ...they need power cord solutions that minimize (eliminate) radiated RF effects to the proximate DAC. This is true, believe it. A DAC's output contains out-of-band noise that is amplified by the amplifier to be radiated back to the DAC itself. By combining my RF Filtered power cord and RF-STOP Cable Sleeve with a battery, an amplifier setup is provided the combined benefit of isolated power and zero radiated RF.
⑥ Source Component Power
Perhaps the biggest reason to incorporate battery power is to prevent RF noise from the digital component chain from affecting the DAC. The source chain generates CPU/GPU/FPGA clocking noise at GHz rates with the ability to send RF energy back up through the AC power supply and into the wall wiring to affect other components. In my system, all digital sources are contains within an RF-STOP Isolation Box with a single filtered AC interface. Alas, even separate circuits or an isolation transformer does not adequately contain these RF energies. Here again, you need to combine a RF Filtered power cord and RF-STOP Cable Sleeve with a battery.
Apologies if my description of an endgame system sounds like a science project. However, at each point in the system, I've identified the root causes of sound degradation and had to design and build solutions that did not exist. Yes I am still working on simplifying things to reduce cost and complexity ...and improve aesthetics. I promise, however, that the system prescribed above is comparable to the best the audio world has to offer ...for a fraction of the cost. I have this reference system for my personal listening pleasure and am working to have a local (Toronto) demonstration venue open later this year. Please contact me for more information.
Next blog, I'll have more on my amazing RF-STOP Cable Sleeve.