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Here’s what I said about the sound at the time after my modifications: "Bass is much more solid and powerful, mids and highs are more crystalline. What I use for listening is Herbie Hancock's River (The Joni Letters) recorded in WAV to disk from CD. As I said before, I'm using a modded Lepai amp (Tripath TA2020) with no caps on the input (because I'm using a transformer). So no caps from DAC o/p straight through to amp input. My test is to get the brush strokes on the cymbals to sound like brush strokes on cymbals with texture rather than a haze of sound - this gets me closer to it with some texture showing through but not all the way. I haven't heard a system yet that renders this properly so maybe it's in the recording. As for the rest of the album, the voices sound amazingly lifelike (Tina Turner, Corrine Bailey Rae, Leonard Cohen, Joni herself etc.), the piano sounds perfect, Wayne Shorter's sax playing is a wonder on this album too and you can just about hear the spit in the mouthpiece."

While getting on with these changes, I was hearing stories about the hiFace sounding so much better than the Musiland. So I got a hiFace an, straight out of the box it sounded nearly as good as my modified Musiland. Back to the drawing board with the hiFace it was then! This already had two oscillators. So now my focus moved to the PS as I'd improved the sound by addressing this on the Musiland. Once again this was being derived from USB power. I put a scope on it to see what noise there was - distinct spikes in the waveform. Here's where I got to synthesize two strands of my thinking. I'd recently found out about a new type of battery designed for electric vehicles - a LiFePO4 battery (that's lithium ferro-phosphate for those who failed chemistry). Its specifications impressed me (particularly its low impedance) and its 3.3V output was perfect for powering digital circuits. I bought some. Looking at the hiFace circuit I realized I could isolate the power to the clocks and run them from this battery.


Here's what I said about the sound at the time: "I removed the clock PS series inductor and fed a clean 3.3V from LiFePO4 battery for a noticeable improvement in sound with much better resolution of instrumental timbre and subtle sounds such as the snare drum and cymbal brushing on Herbie Hancock's The River (my test record) - Corrine Bailey Rae now sounds quite good singing the River or maybe I just got into it after listening to the album for so long. This really is a big step up in SQ - not surprising that a cleaner PS feed to the clocks will improve matters."


After some more mods I said this: "This is the best audio I've had in my system to date - I reckon it would compete well against the best." The scope confirmed what my ears were hearing with a nice flat line - no spikes! I shared all my findings (particularly the sound quality differences on my favorite Herbie Hancock track) in the public domain on a DIY audio forum. Some people tried the modifications themselves and found similar things. Enough people contacted me who were hiFace customers asking to have me do this micro surgery on the SMD components on their hiFace board. That’s how I started to do it as a service. Eventually it evolved into a more user-friendly boxed component - the MK1 hiFace.

The move to a Mk2 was precipitated by my nagging awareness that the MK1 still had some improvements outstanding that could be applied to it:

  • It still used the 5V power from the USB buss for some circuits. When I applied external 5V instead of USB 5V it did improve the sound. I advised some MK1 users how to do this by cutting into the USB cable and tapping an external 5V supply into it - effectively dispensing with the noisy USB supply from the PC.
  • Charging the LiFePO4 battery is a bit of a pain. LiFePO4 chargers are not yet widely available.
The MK2 fixed both of these niggles and came with a 5V supply and a LiFePO4 battery charger already inside the box. There were one or two other improvements too. All this improved the sonics once again by making the MK2 immune from the low quality of the PC's power supply and the kind of USB cable used. It also made for a more user-friendly device.


The MK3 evolved from the thought that the S/PDIF transmitter chip (DIT4192) runs off 5V power. If I replaced this with a WMM8804 which runs off 3.3V power, I could dispense with the 5V external supply altogether and run everything off battery. I was also aware that the output transformer in the hiFace caused some overshoot on the S/PDIF signal on my oscilloscope so I decided to try it without this transformer & correct the output impedance to a true 75Ω for S/PDIF. The S/PDIF waveform now had no overshoot and was s clean as I had ever seen from any of the various S/PDIF devices I had looked at on the oscilloscope.


I wondered if the lack of a transformer and therefore galvanic isolation on the S/PDIF output would allow noise to bleed through from the PC/laptop through the MK3 and into the DAC, amp to eventually be discernible at the speakers. No such noise was evident. The background between songs and in the silent gaps in songs was an enveloping blackness. There was no difference in sound when I had the laptop charger plugged in or when I ran the laptop on its batteries. I later changed my laptop and did hear a very slight haze and whine in the sound. This went away when I unplugged the laptop charger. The cause of this noise was a ground loop. The laptop charger had a grounded mains plug which set up a ground loop with my DAC & amp. The easy solution was to use a double adapter from which I had removed the ground connection. Result? Enveloping blackness and happiness again.
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