Qudelix-5K Bluetooth USB DAC AMP with LDAC, aptX Adaptive, aptX HD, AAC (Dual ES9219 3.5mm Unbalanced & 2.5mm Balanced Output)

Hi.. I'd like give my view on Qudelix 5K after using it for almost 3 months. Hopefully what I share below could help others to understand better about this device.Qudelix 5K is a very sophisticated audio device. I notice it captures firstly/mostly the 'serious' audio lovers/enthusiasts. I myself like it so much and really amazed by its sound quality that I feel it necessary to introduce it to greater audience than just the audio enthusiasts. For this reason, I'm going to try explain it in a more simple than technical approach.In simplest term, device like Qudelix 5K can do two things:1. As Bluetooth receiver (receive BT audio and send out analog audio)2. As USB to analog audio dongle (USB-C to analog audio out)The USB-C port on 5K is dual function port. We could use it to charge the battery on 5K, or use it as interface for USB-to-analog audio dongle, or both.Qudelix 5K send out analog audio via the 3.5mm or 2.5mm jack on top of the unit. On either of this port we could connect earphones/headphones or send the output across to the external audio amplifier (i.e. home audio or car audio).(Note: the 2.5mm port is intended to operate in 'balanced' audio mode. If you have no idea what it is all about, please avoid to use it. Don't try to put in just any 2.5mm plug/cable, without proper 'balanced' wiring. 5K could be damaged by the wrong 2.5mm connector/cable.)Depend on how we like to use 5K, how deep we want to dig 5K capabilities and tinker with their accompanying mobile app, we could turn this device from sounding great to amazing.We could use Qudelix 5K just as simple BT receiver/audio dongle. The device have been pre-set up by manufacturer with optimum default settings. IMHO, the default settings on 5K is more than enough to make average/most listener to be happy with it. Enough to open them up to the world of improved audio reproduction and that while having the freedom of detached (i.e. wireless) earphone/headphone from their mobile phones.Please don't feel degraded/depreciate when I mention 'average'. By 'average' is I mean for people enjoying music more than concerning with how their audio equipment perform (that's why there's the term 'audiophile for this kind of love :) ). I myself is more of a music lover (80% of time) than audiophile, though I really love to hear my music sounding their best.Qudelix provide 5K with an accompanying mobile app (available for iOS on AppStore and Android on PlayStore). The app is intended to do many things such as:- to regularly upgrade the 'software' inside Qudelix 5K; to improve its performance and stability- to formally start the warranty of the 5K with the manufacturer- to adjust behavior when it is connected as USB dongle- to enable/disable certain Bluetooth audio codecs (note: by default all codecs are enabled)- to adjust the buttons behavior/actions- to adjust the power/battery management- to adjust it to get the maximum sound quality (remember: this one is not mandatory to get good sound out of 5K, as I mentioned above)- to set the built-in equalizer in 5K to adjust it to sound more to our flavor (note: human hearing and ear profiles are never the same person to person), or to 'correct' the imperfect characters of earphone/headphone, or compensate the room response of home/car audio system.- and few moreThe interesting part with the app is, the Qudelix app is actually just a user interface to set these settings on 5K. All the settings we do on the app are not saved on the app but directly on 5K and the app is no longer needed for 5K to perform. Settings on 5K will follow it everywhere regardless of the mobile phone or computer using 5K as BT receiver or USB audio dongle. So if in one occasion I used 5K with my friend's mobile phone or I used to test a mobile phone in the store, all the settings (including the sound profile) will just follow with 5K.With such capabilities of Qudelix 5K, the app then is a little bit complex to use. You'll need time to really understand and to use all the features. I myself confused on my first time using it. But don't feel too overwhelmed but the app, if you found it is too complex to understand it, just leave it. Qudelix 5K sounded already good with its all default settings.I don't want to cover all the settings and Qudelix capabilities here. Those could be found on their user guide. I'm going to list the things that I found amazing on Qudelix 5K.1. Amazing Sound.I've repeated this many times above. It simply sound amazing. Be it used with just basic AAC/Apt-X codec, or very advanced codec like LDAC, or using as USB-audio dongle. It sounded many, many times better then my other BT receiver Maceton WM4U. It sounded two or three levels above my LG V20 phone; a phone that is highly respected for the sound quality: better resolution, better music layers, better power, more finesse.2. Long battery life.This depend whether we want to maximize it for longer battery life or set it for best audio performance, we can get between 10 hours to 20 hours of play.3. Powerful Driving PowerDevice like Qudelix 5K is technically referred to as DAC (Digital Analog Converter). DAC will receive audio in digital format and convert it into analog audio. Analog audio is then converted by the interaction of amplifier and transducer (i.e. speaker, headphones, earphones, etc.) to become audio wave so that we human can listen to it. Normally analog audio output from DAC alone is quite low and need external amplifier to sound louder. In Qudelix 5K case, it has built-in little amplifier that is powerful enough to drive various headphones/earphones load. The 3.5mm port is powerful enough to drive many headphones. But the 2.5mm balanced port would deliver double of power. In balanced, it's quite powerful to drive my very demanding Hifiman HE5LE planar magnetic headphone to sound quite loud.4. Amazing Bluetooth range.Qudelix hype about the 5K unique BT antenna design, and they are not just hyping it up. I could get 5K play 8 meters away from my LG V20 phones, across 3 layers of brickwall (of about 6 inch each) at my home and that while I use LDAC as codec, and that streaming from my LG V20 that can only do BT4.2.5. Amazing EqualizerQudelix 5K come with two flavors of 10 bands equalizer; Graphic Equalizer (GEQ) and Parametric Equalizer (PEQ). Equalizer is done on digital domain with 64 bits precision calculation, which mean the EQ could adjust the level of frequency and amplitude of the sound without degrading the quality of the modified sound. GEQ is something that most people familiar with. But PEQ is a beast of equalization tool. It provides a much more flexibility for us to shape the frequency of the sound to affect the response of our earphone/headphone or room response of external audio system. Note that PEQ is usually considered as professional tool. But not necessarily professional audio equipment would have PEQ in it. Some lower/mid end even only have 3 to 5 bands PEQ. Amazingly 5K come with 10 bands very high precision PEQ in such a small package.By now, you should be able to see why I mentioned that Qudelix 5K is such a sophisticated audio device. Inside its understated appearance, Qudelix 5K is really an amazing, highly customizable and state of the art audio device.Below is the list of audio device I used with 5K this far.Earphone: Sony MH755, Blon BL-03, Fiio FH1Headphone: Drop E-MU Purpleheart, Audeze Sine (in balanced), Hifiman HE-5LE (in balanced)Source (BT transmitter): LG V20Music/songs: I don't limit myself with certain genre of music. I listen everything: classical/romantic/baroque/renaissance, rock (progressive, rock'n'roll, hard rock etc.), jazz (all derivatives), metal, pop, folk/country, vocal, etc.PS. Qudelix 5K has built-in microphone, which is very sensitive, but don't have noise cancellation. The voice coming out from the microphone is actually very good, but if we clipped Q5K to clothes it could easily pickup the noise of 5K rubbing the clothes and send across the sound to the other end. If we don't like this, and our earphone has built-in microphone, we can turn the 5K microphone off and instead using the external microphone on our earphone/headphone. In the other way around of usage, if our headphone/earphone don't have microphone (or we send audio output to amplifier for example) we could use the built-in microphone on Q5K for making a call.PPS. Comparing Graphic Equalizer (GEQ) and Parametric (PEQ).In GEQ, frequency range of human hearing (20Hz to 20KHz) are divided into about factor of two frequency scale (31.5, 63, 125, 250, 500, 1K, 2K, 4K, 8K, 16K) with fixed width of frequency range 'impact' for boost or cut as peak/valley. PEQ is a much more sophisticated equalizer in that this frequency scale can be adjusted freely by us, for how wide the impact would be, and whether the impact is affecting as peak/valley or as shelfing filter. Don't be confused and overwhelmed by this PEQ. It seems complicated at first but is really not that difficult to use. What makes it complicated is to effectively use PEQ to shape a headphone for example, we would need to have the frequency response measurement of the headphone. With that we will know on which part of response the phones are the lacking or having too much of volume. Then we rectify these with the PEQ. Luckily some sites readily share their measurements such on this list: https://www.reddit.com/r/oratory1990/wiki/index/list_of_presetsThe PEQ sample I attach as one of picture, show my way to correct the response of my Fiio FH1 IEM. I don't follow any 'Harman' Curve but use other excellent sounding IEM for reference. Without the EQ, it sounded smooth but flat and unexciting. PEQ turn it into a lively sounding IEM I could never imagine before.

I was an early buyer of the Qudelix in January 2021, after its original hype. After ~3.5 years and 957 hrs (tracked by the app) of abuse on my original unit, I think that my original unit is finally at its end of life. I did not baby my unit at all, using it for everything from at home listening, walking around campus, working out, running, sports and riding motorcycles. During that time, I was never really conscious about excessive wear, or worried that I would break it either. Since there are tons of reviews of what is so good about this as a DAC/Amp and its software features as a general audio product. I want to focus my review on some of the parts of it that have failed over the years, and some of its less talked about features.The main things that have broken over the years are as follows.1. The MEMS MicIn it's early days, the Qudelix received multiple and frequent firmware updates quite regularly. This was good, but during one of the earlier firmware updates It completely broke the MEMS mic, and it was never fixed in future updates for me. This didn't really bother me since I barely used it, but still kind of a shame.2. The pocket clip.The integrated pocket clip was one of the most used features for me for the Qudelix. I used it practically every single time I used the device. After about a year and a half of use, I could feel that one side of the pocket clip was loose, and that the plastic was cracked on the hinge where the clip connects to the main body of the device. I continued to use it like normal, but after another ~2 months, the plastic fully broke and the pocket clip fell off. I "fixed" this by using a piece of kydex and epoxy to make a new pocketclip, that has held up for over a year now. Not nearly as good as the original, but still better than nothing at all.3. Automatic Output Switching.I honestly don't know what happened, but one day, I remember plugging in the device single ended, and I heard weird one channel/poorly grounded audio from the device. After checking, I saw that the app said it was outputting to balanced. This was weird, because normally, it could sense when I was plugged in balanced or single ended without issue. After trying to fix it in software, I just gave up and ended up setting it manually in the app which fixed the problem.4. The battery.After all these years, the battery life on my unit is noticeably worse than the new one I just bought. I would say that It gets about 60~70% as much as the new one, which is pretty expected after +3 years. I did not use the 80% charge limiter built into the app, but I still think the battery has held up pretty well.If this becomes an issue for anyone. There is a teardown video, and 3rd party replacement batteries available, for under $10 USD. It requires a security T6 screwdriver, a pry tool, and a soldering iron.5. The 3.5mm JackThe final and probably most important thing that broke, that made me want to replace this was the 3.5mm jack. Around the 3.4 year mark, I noticed that the connection would seem loose in the 3.5mm jack and I had to twist the cable a certain way in order to get both channels to output. One day I ended up pushing a cable too far into the jack, and it ended up breaking the jack entirely (see photo). I was able to disassemble it and pull the jack back out, but it did not fix the connection issue. I have a photo of me replicating the issue on my old unit. I should note that this issue is also probably fixable if you are willing to do SMT soldering, but with all the other issues that have piled up over the years, I figured it was just time to buy a new DAC/Amp.Again, I still believe that this is a really good device. With amazing features that make its competitors look laughable. But there are a couple of things I would really like to see in a potential version 2.1. I would really like to see either some reinforcement on the plastic hinge where the pocket clip connects. The metal of the pocket clip is really nice, but it would be nicer if either the hinge was more durable, easily fixable/replaceable or just made of metal.2. Replace the 2.5mm balanced jack with 4.4mm. I personally hate 2.5mm and judging by the way the industry is going (at least in 2024) people agree with me.3. Allow me to set a volume of the output when the device is turned on.Let me explain, when you turn on the device, it makes a beeping sound, that is entirely dependent on what you had the amp volume set to when the device is turned off. So, for example. If I was using full sized headphones at home with this with the volume set to 90dB, which with an EQ gain of -5 drops it down to 85dB. I finish using it, and turn off the Qudelix. The next day, I forgot I had it that high and turn it on with IEMs plugged in, The on sound will play at over 100dB. This is really annoying and could honestly just be fixed with a simple firmware update.Anyway, here is what I, as a habitual user of this device want in a potential version 2. I would like the above features to be implemented, even if the cost of the product is slightly higher. I would definitely buy it. The main reason I even considered getting a BTR 15 instead of another one of these was because it has 4.4mm. Also, if a potential version 2 was a slightly bigger, and had more battery life, That would be nice as well. I would really like this to have battery competitive with other wireless options like APP2.All in all, even with "only" 3.5 years of use on my unit, I think I got more than my money's worth. I believe that this is the most feature rich, and usable portable DAC/Amp on the market, with only a few minor flaws that could be addressed.