This next step in the process came about a day after the Teradak was in the mix, during burn-in period. I found that the audio had suddenly become a little bright/harsh again. After extensive testing, what I found was that the fuses and power cords for the Oppo as well as the Teradak/DirectTV “digital transports” were influencing the audio coming from the Krell HT Processor. In additional, a fuse in one source transport was influencing the sound from another source transport, even though it wasn’t selected as an “active input”, or was put in standby mode. The DirecTV Genie receiver is always powered up and running even when it’s in “standby” mode (internal computer and DVR are 24/7).
This discovery came when I decided to remove the Hi-Fi Tuning silver fuse from the Oppo and put in a 2A PADIS fuse instead. The result was, even though the Oppo was powered off and in “standby-mode”, the sound from DirecTV was not as bright, but just did not sound right in the end.
At that time, the Oppo had the PADIS fuse, but had a power cord that uses cheap braided 20awg solid-core Radio Shack copper with Furutech rhodium connectors. In other testing, I found this Radio Shack copper sounded good, but it was too warm with rolled-off highs. Interestingly enough, this power cord on a digital HDMI source was affecting the sound from a separate DirectTV digital HDMI source through the Krell HT processor. I switched the power cord on the Oppo to a much better braided 20awg solid-core OCC copper teflen Neotech cable wit Furutech rhodium connectors. The sound quality improved immediately. Weird! In research, I think there are two wires in the HDMI cable that could contribute to this result:
Pin 18 - +5V DC
Pin 17 – Ground
Pin 18 is +5V that is supplied by the source device to power external items that do not have an external power source (this would be something like active cables or external headphone DACs or something else).
Pin 17 is ground, which is the ground plane shared across all devices in the equipment chain).
Since the +5V DC voltage is generated by the Oppo or Teradak, I believe it is making its way into the Krell processor (through the HDMI input) to the normal 5V power rail. This will definitely influence the character as the DAC href uses this +5V voltage for generating it’s DC output voltages (among other things in the circuits). The ground plan can influence sound as well between devices. It could also be that the power supply on the transport is affecting how good the digital signals are (voltage levels, jitter, etc.).
So, under testing, putting a warmer fuse into the Teradak (such as an Isoclean) definitely contributed to making the audio sound warmer in the whole system. In the end, I ended up with Furutech fuses in both Oppo and Teradak and Audioquest NRG-4 power cables with Furutech Rhodium plugs. In the end, that was the best combination as the Furutech fuse / OCC solid-core cables are my reference in all applications. Both the video quality and audio quality are absolutely amazing for me now.
To sum it up, the argument that “switching power supplies are not bad for digital circuits” is completely wrong for me. I can hear the difference! It’s amazing to me that many high end audio equipment pieces still use switching power supplies for digital sections (even though they may use linear power for analog sections). Emotiva started on a crusade a few years ago when they started touting “switching power supplies as the future”. I believe they were paving the way for consumer belief so that they could put in switching power supplies and make the item lighter/cheaper for shipping. I have also read many electrical engineer statements that switching power supplies are perfectly fine as long as you have a good filter in them. I strongly disagree!! In fact, one of the reasons I love my Krell S1200 is that it does not use switching power supplies at all! It uses linear power for everything. In fact, it actually uses a fully discrete shunt regulator circuit for the +5V DAC vref, and a normal LM7812 regulator for 12V required for some digital circuits.
So, new project on my list for next year is to upgrade my computer power supply (upstairs computer audio system) to a Teredak Computer Linear Power supply and upgrade the DAC to something that uses non-switching power supply (maybe LKS MH-DA004).