This is a review and detailed measurements of the Audiophonics I-Sabre V4 DAC "HAT" for Raspberry Pi single board computers. It was kindly sent in by Audiophonics for review. The cost without VAT is 58.25 Euros which translates into US $58.25.The I-Sabre V4 looks unusual as far as layout:A lot of board space is dedicated to the 3-pin IC to the center left. Lots of via stitches are used to allow the PC Board to act as an efficient heatsink.There is a socketed 1701 op-amp which I assume allows people to scratch the itch of modding such devices. There is a proper oscillator in that larger "can" enclosure feeding the little ESS ES9023 DAC chip close to the RCA connectors. Speaking of those, as you see in the picture, they are quite beefy and high quality. And the large nut should allow secure connection to an external case.There is a connector on the left for a display and different headers for switches and such.Finally, there is an input for 5 volt in addition to what power the Pi can produce. I started my testing without it at first but then added it as you see later.There is an extended socket that mates with the PI board with plenty of space below it for cooling of both components.Let's stream a 1 kHz tone to the board and see what we get:Nice to see nominal 2 volt output. Performance is good in one channat at SINAD of 89 dB but not so in the other channel. I thought this was a power issue so I added the second power supply. In the process of that, I realized that there is some grounding issue as touching the outside of the RCA jacks resulted in improved performance (!). Used some grounding wires and got most of the way there without having to hold my hand on the RCA connector forever.Issues like this is why I recommend balanced XLR outputs in DAC. Anyway, even with improved grounding performance is still a bit shy of the cheaper HifiBerry DAC+ Pro Jitter with and without the grounding/second supply shows what I was struggling with above:Multi-tone testing shows high level of intermodulation distortion products filling between our 7 primary tones:And here is the response to white noise, indicating the response of the reconstruction filter:One channel is show less attenuation and that single spike. There is definitely some noise issues here.The build quality of the Audiophonics I-Sabre V4 DAC is quite good. Measured performance though, falls a bit short of cheaper HifiBerry DAC+ Pro. Measurements and some clean up of the design may get it up there but there is still a price premium. I am not here to gauge the usefulness of the extra hardware features. If those are important to you, then perhaps the price could be justified.As it is, I am lukewarm on I-Sabre V4 DAC and can't recommend it. What I can recommend is Audiophonics as a store and company to do business with. For them to volunteer to send their product to me and participate here means a lot. So if you live in Europe, and have a need for the large suite of products they sell (both their own and not), give them some consideration.------------As always, questions, comments, recommendations, etc. are welcome.Summer is sadly fading out into fall and with it, cooler weather will be upon us. And rain. So the panthers are hammering me for appropriate clothes to stay warm and dry. Problem is, I am tired of spending money on them so please,what you can using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/