This is a CMOY amp. It is a portable pocket headphone amplifier. It’s easy to build, and sounds pretty good. You can read about it from here: https://tangentsoft.net/audio/cmoy/
I use this pocket amp not to make my headphones louder, but to make them sound better. Larger headphones are harder to drive, and even if you get sufficient volume levels from your phone, you may be not be getting all frequencies at the same volume, and you are likely getting distortion, even if in small amounts. I want hear my music, not cheap amps. I haven’t used this thing since I got the LG V20 last year. LG’s V20 not only had the most powerful headphone amp of any phone at that time, it also had the best digital to analog audio converters.
Nobody can listen to digital music, nor can any headphone jack produce digital audio, and no set of speakers can play digital sounds. We hear in analog, and our devices have to convert digital signals back to an analog signal before we can hear it. The conversion of a digital audio signal back into the analog realm is dependent on a DAC, or digital to analog converter. Every phone and tablet has a DAC; but most are not great. Not so with the V30+, the latest flagship phone from LG and the best phone of 2017.
The DAC in the V30+ not only creates the smoothest analog on a phone or tablet, it allows you to tailor how it does it using a choice of three filters.
The V30+ also has some equalizer presets. Personally, I would strongly prefer to have manual EQ controls, but the sound of this phone is so awesome, you really don’t need the EQ at all. I usually just leave it flat, or "Normal".
Included in the box is a pair of LG ear buds. They didn’t use another brand, or use theirs, and re-brand it as someone else, it’s just a humble looking pair of ear buds that are simply labeled “LG”. I didn’t know what to expect; so coming in with no expectations I have to admit, I was greatly impressed. Everything I played through these sounded full, warm, and natural. No frequencies are exaggerated, nothing is too bright or harsh, and nothing is muffled. In other words, they have perfect sound balance. They are pretty comfortable too. Coupled with the amp and DAC on the V30+, music comes alive.
I’ve been testing these earbuds and this phone with Amazon Unlimited Music, Google Play Unlimited Music, and Tidal. Really, all of these services sound great at the best quality settings, but nothing compares to Tidal, which is using FLAC lossless compression instead of the lossy compression of all the other services. If you care about how your music sounds, and if you want to hear details and layers you never realized were there, try Tidal with the V30+.
By the way, there isn’t a 9 volt battery in my little pocket headphone amp, because it is superfluous after getting the V30+.
Disclaimer: The Product Ambassadors are Sprint employees from many different parts of the company that love technology. They volunteer to test out all sorts of Sprint devices and offer opinions freely to the Community. Each Product Ambassador shares their own opinions of these devices, therefore the information in this post does not necessarily reflect the opinions of Sprint. The PA's do not represent the company in an official way, and should not be expected to respond to Community members in an official capacity. #sprintemployee