This is a review and detailed measurement of Radson Earstudio ES100 portable Bluetooth, DAC and headphone amplifier. It was kindly sent to me by the company year and half ago and for one reason or the other, has been waiting for this review.The ES100 costs US $99 on Amazon including free shipping.Despite all the functionality and included battery, the ES100 is quite diminutive in size:On the flush side that you see, there is a lit ring that changes colors. I am not a fan of such status indicators and have to keep fighting trying to figure what status it was in.Here are the controls you get:What sets the ES100 aside from dongles and such is its app in Android and iOS that gives you very detailed control over operation of it. One very useful feature is setting the amount of power available from either 3.5 mm and 2.5 mm "balanced" headphone connections. That said, one of the settings can cause damage to the device if used incorrectly. I would have wished the device was more resilient that way.Testing Bluetooth devices is challenging since my analyzer cannot control them directly. Fortunately the ES100 also acts as a USB DAC on Windows. Alas, it only supports 16 bit resolution on Windows whereas it supports 24 bits on Mac. I have not seen such discrepancy in the past and it impacted one of the tests negatively.I should note that I received exceptional support from the designer when we started our conversation about reviewing the ES100. He seems quite knowledgeable and approachable which is a major plus in my book.All the tests including this dashboard were conducted by using the ES100 on Windows. With phones depending on the software you use and especially with Bluetooth, you may get degraded performance.I had to reduce the input level by 4 dB to get the ES100 to not clip resulting in less than optimal 1.1 volt output (for DAC use that is). Phone dongle don't do better anyway so in this market segment, that is not an issue.SINAD (signal over noise and distortion) was good enough to land in the "GOOD" category of all DACs tested:Intermodulation distortion versus level shows the clipping behavior well:Linearity was impacted a lot due to 24 bit to 16 bit truncation (rather than dithered):Most important test for headphone amplifiers, especially in this category, is the amount of power they have. Fastest way to get bad sound is for an amplifier to run out of juice and clip. So let's start with 300 ohm load which would represent high impedance headphones and ability of the amplifier to produce high enough voltage:The 3.5 mm jack provides a bit more power than competing dongles like Apple USB-C . Where the show gets interesting is using the 2.5mm jack in high mode. There, we get quadruple amount of power which is quite significant. Noise level is higher though so performance with sensitive IEMs may not be good.Stepping down to 50 ohm load we get:I am not sure if the jack is lose or not but I got pretty different results in one channel versus the other (red vs blue) with 3.5 mm output. Power was limited to 23 milliwatts. Switching to 2.5mm in low mode (high mode is not allowed for impedance < 300 ohm), give us more than three times the output which again is significant.Stepping down even further into 33 ohm load we have:I don't have a balanced 33 ohm load so I am showing the two modes for 3.5 mm output. As you see, they almost make no difference even though one is said to have more current than the other.Putting these in rankings for 300 ohm we get:All the devices that have more power also use a lot of power and don't have their own batteries as ES100 does.Here is where we stand in 33 ohm with me estimating the power the ES100 could produce:I wanted to test the 2.5mm "balanced" output but unfortunately all of my balanced cables terminate in XLR. I bought an adapter to 2.5 mm on Amazon which should be here by the end of the week. So for now, my testing is based on 3.5 mm output.On both of my test headphones, the Sennheiser HD-650 and Drop Ether CX, there was good amount of output. I suspect these larger devices with batteries included have better peak output than testing indicates. With the increased output of the 2.5 mm, both of these should sing a lot louder and bring with it more impact.The Earstudio ES100 is a pretty unique offering ranging from its included battery to nice control through its mobile apps. Dongles rely on simplified heuristics to determine available power which easily misfires, underpowering headphones. Not so with ES100. In addition, the ES100's included battery means you are not draining the power out of our mobile device as much as a dongle would.So overall,--------As always, questions, comments, corrections, etc. are welcome.They say you should feed your pets fish to get them to have a shiny coat. So I went on Amazon and they want $35/pound for dried fish for dogs! Even though my panthers don't have any fur, you wouldn't want them to have dry ones, do you? So let's all get together andto buy a few pounds of these fish treats using : https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/