MINI-Review: FIRST IMPRESSIONS HDPI do have some "sneak-peak" impressions. Total listening time has been only two hours last night, and tonight I will listen again after a 24 hour break.
I have tried it as a 24/96 USB DAC with some 24/96 hi-res music from HDTracks.com (Nancy Bryan), using very hard to drive 25 ohm 87 dB/mw head-direct HE-5, and 300 ohm 102 dB/mw Sennheiser HD600, and 32 ohm Grado HF-2. I enjoyed the HDP with all of them.
I also tried my very sensitive Westone 3 earphones, and there was no hiss or noise. With these very sensitive IEM, when the volume is turned down close to zero there is a very slight channel imbalance, but one can easily turn it down low enough to go to sleep with music and IEM and not feel like it was too loud in one channel or both.
The HDP manages to drive the inefficient HE-5 better than I would have expected, since these phones usually demand an amp with 2 watt output at 32 ohms. Still, my maxed Woo WA6 can drive the HE-5 decently, and the HDP does similarly well in terms of having enough power to enjoy them. Volume levels will not be earsplitting like with a 2 watt amp, but it does play louder than I like to listen to my music. With HD600 it seems to be a little better match, as well as with the Grado HF-2. I do feel like the HDP needs to burn in a little to open up and become more refined, but fortunately it is NOT bad sounding in any way out of the box. It seems to be tuned for strong tight bass, to my ears, which makes me happy.
I also tried it as a USB DAC preamp with analog out feeding a homebuilt eXStatA electrostatic headphone amplifier and some HE Audio Jade electrostatic headphones. It seems to be a very detailed source, and didn't seem to need a lot of burn-in as a preamp, offering good depth into the music. It's a great choice to drive this particular "stat" amp because the person who built the amp made it with separate left and right volume knobs (he's building me the same amp with a single volume attenuator). So, I could use the HDP's single volume knob to adjust the volume, instead of twiddling with two knobs on the amp.
And, with the stat amp's two volume knobs turned up to maximum, the HDP and amp were silent (at least in my noisy house). This is normally a balanced headphone amp, but it can be driven single ended with a simple RCA to 3-pin XLR adapter, without the need for my input transformer box to convert from SE to balanced. When driven single ended this way, the amp's volume will be about 3 dB lower, while gain remains at 1000. The HDP did not have a problem driving the eXStatA amp to be as loud as it would have been with a higher level XLR balanced input.
I was very pleased to see the 3.5 mm input doing double duty as an optical input. I was afraid the digital would be USB and coax only, and it's fantastic that optical made it in there. I will try the optical and coax as I evaluate the HDP later. I will have more time this weekend to listen to it, and I will let it run 24/7 with my Westone IEM to burn-in in between listening sessions.
EDIT - I haven't planned to post much more until burned in, and then I'll post something in it's own review thread. This a sneak peak to let people get a glimpse of what's ahead. I am testing the prototype as Jason stated here or somewhere else, so I can't post photos because the layout does not match that of the final product, but as I suspected in a previous post the HDP is built around the Icon and Icon amp cases.