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Thread: 6TX - Review

  1. #1
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    May 2016

    6TX - Review

    First impressions is that this is a really nice amp! (Very well done Robert!)

    I am definitely no audio professional with no special qualifications in this field, but I do appreciate good engineering and attention to detail and will give my comments on this amp based on my experiences and understanding. I am a bass head who loves sub-bass extension whilst keeping everything more flat. I also try to listen at lower volume levels where possible. I enjoy listening on speakers with a sub, or sub-bass boosted bookshelf setup for that flat extension to 30 hz (at the expense of spl) With my headphones however, I have forever been searching for phones that give me that sub bass extension, tonal balance, accuracy and most importantly, without that mid bass hump. The fact that I want to listen at lower listening levels also doesn't help due to the ears diminishing sensitivity to low frequencies at low volumes. I always find myself turning up the music to hear the bass I enjoy but would rather find a way to avoid that. In short, combined with capable phones, this amp is the medicine I need for this disease.

    I have here for review a 6TX amp with normal bass boost. I don't really use any super high resolution audio sources, I play Spotify on 320kbps streams, and my audio devices are an iPhone 6 Plus audio jack, MacBook Pro Mid 2014, HRT Micro Streamer, and the USB ports on the MacBook and on an Asus H97I Plus running OSX 10.13.2. My tested earphones/headphones are a Hifiman RE0 (earlier cloth cable version and newer plastic cable version), Shure 535, Shure 846, Fostex TH-00X Mahogany and PH

    - The amp is heavier than the 4G, giving it a nice solid feel. It's still such a small amp weight isn't a practical issue, but since its mostly case material and battery weight, it's understandable and does give it a great feel in the hand.
    - The stainless case is a bright metallic colour, reflective and shiny which makes it difficult to photograph and reflect its natural colour. The polish is smooth and attractive, somewhat of a fingerprint magnet though for those like me to like to keep things clean and unmarked. I find myself wiping the case down regularly.
    - The end panels are a beautiful concave surface with a light matte finish. It is an amazingly precise fit with the steel case and really contributes to the super tidy look. Bonus points for the symmetrical face layout which shows an extra special attention to design, this really appeals to someone who will layout electrical components on a circuit board symmetrically just because.

    I've had a few weeks with the 6TX and had a few good listens with my couple of headphones. I also have the Headstage 4G and is the main point of comparison, along woth other DIY amps. I've also used a small Fiio clip amp, and a Teac AL-101 but those two cannot compare at all.

    - My very first impression with the 6TX is that there is very good bass extension with this amp. The 4G had a bit of rolloff in the subbass region, but the 6TX has no issues with bass extension, allowing real deep notes to be reproduced as it should be.
    - Mids are reproduced well and had no issues here. Perhaps I wasn't paying too much attention to this, but I didn't notice anything.
    - Highs are a touch less forward, with a rolloff that takes the edge off most percussive instruments. This is the 6TX, which is described as the 'slightly warm sounding' amp, and fits the description well. The treble is there, just not at the forefront of the soundstage. For sligtly hot sparkly headphones it will take the edge off a little, such as on my TH-00X. It could however add to the rolloff such as on the mid focussed Shure IEMs 535 and 846. On the RE0, an IEM described as having great treble extension, I can notice the loss of that range. I personally do miss it and find the 4G better in this regard.

    I am awaiting a 6NX which hopefully has a flatter treble extension and less rolloff.

    *Tone controls
    These are the highlight of the amp, and one of the main reasons why I will use an amp for my phones. I am not critical to the point of expecting absolute reproduction of every single sound as it was recorded, I am perhaps more inclined to appreciate a technical reproduction that approaches accuracy, but with a sonic profile that is enjoyable and to my liking.

    Having fiddled around with a range of speakers, DIY and bought, earphones and headphones, I have come to realise that I enjoy chasing technical accuracy, but tonal balance or its sound signature is really just as important. A system that is able to reproduce something perfectly flat and accurate is not realistically not going to happen, amd I might not necessarily like the sound of it. Tonal balance or sonic profile is ultimately really something that is highly variable between different products and is highly subjective anyway! Why else are we always on the search for the 'perfect' phones.

    My perspective is that using a tone control is not taboo, and something I am happy to use to increase enjoyment of music. The trick is finding phones technically good enough to have no major flaws, only requiring an adjustment to its overall tonal balance and thus correctable with basic tone controls. The other part of the trick is having a tone control thay actually helps.

    *Bass Boost
    Especially in the genre of electronic music, a healthy dose of sub-bass can be well appreciated. I am however quite adverse to mid bass bloat and this is really where the 6TX offeres a simple but effective set of bass boost control. Having two switches is the biggest improvement to effective bass boost control. Bass boost on an amp is doing a similar job to a subwoofer you add to a set of bookshelf speakers, you are adding bass to a system that rolls off early. The two controls are level and crossover, or on this amp, Bass (0,1,2) and Freq (L,M,H).

    Level adjustment is the bass boost switch position 0, 1, 2. This adds a quoted 6bd or 9db of bass boost. Back to our speakers analogy, your subwoofer produces deeper bass, which your main speakers are not producing. You would choose a subwoofer volume level that allows for a match between the sub and mains so that all frequencies are produced evenly. (or to taste ;P)

    Crossover is just as critical and controls the frequency below which you are adding bass. In an effort to create a balanced low end sound, you want to add bass at the point where your main speakers/headphone/earphones start to rolloff. Set to Low, you will add only the deeper bass notes, appropriate for capable speakers/headphones/earphones in the bass department. If your speakers/headphone/earphone roll off early and even the mid bass is weak, then the H frequency setting is for you.

    Using the High setting on capable speakers/headphones/earphones will mean there will be an overlap of bass addition, and you end up with a doubling up of bass in the overlap region, or a mid bass hump in its response. A bloated mid-bass puts me off very quickly! Apart from being wrong, it reminds me of consumer systems where mid bass is simply 'more bass' to the masses, and unfortunately systems are made this way as its technically easier to make lots of mid bass that the consumer hears as bass, whilst it is much much harder to generate real sub bass extension.. Might have gathered by now that I'm a bass addict :P

    This amp delivers VERY well in this regard! The normal bass boost option with 6 or 9db boost has enough kick with the 9db option to bring most reasonably capable phones into a fairly nice sounding set. On the Shure 846, a bass capable IEM, using the 6 or 9db option and Freq L position gives a great sounding bass boost to give weight to kicks and bass lines, making up (partly) for the lack of visceral kick only speakers can produce. There was still some mid bass boost in the L position but FAR better than any other amp I have tried on the market, with an effect that is described as an extension of bass without too much bloat. This is refreshing and makes this one of the best bass boosts you can get (this alone is the main reason I will go to the effort to amp my phones)

    With my RE0 IEMs, these phones have decent extension, but are simply lacking in bass quantity. These need a bit more bass boost and ended up on the 9db and L setting to have a nice amount of bass without the mid-bass boost. I also tried a friends RE0, the newer generation with a plastic cable, however the low end extension of these phones are more limited so they needed an extra boost in the higher bass notes so the frequency was set to the M or H position.

    On the Foxtex TH-00X, these are V shaped headphones, and already have a nice capable bass extension. using the bass boost on 6db was sufficient and definitely on the L setting for frequency. There was definitely plenty of bass here.
    Last edited by okwchin; 07-02-2018 at 05:22 PM.

  2. #2
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    May 2016
    *Treble Boost
    Treble boost is something I use occasionally, especially on the Shures which coming from my other phones or speakers, could do with a little more extension. This is one area the 6TX doesn't tick the boxes as well for me. As the 6TX is the warmer sounding amp, there is already a little bit of treble roll-off. Combine this with the mid centric Shures and we begin to lose a bit too much extension. The treble boost is on a single switch with three positions, off, 1 and 2. Switching to position 1 adds to the treble and recovers some of that sparkle, while position 2 adds even more. Position 1 feels about right with regards to the high extension and is similar between the 4G and the 6TX, however there is a difference between these amps with the frequency that the treble boost covers.

    The treble boost on the 4G was great for me as it worked on the higher treble only, allowing me to add to extension and pickup where some phones fall short. The 6TX however has a treble boost that also affects the lower treble or the high mids. This meant that female vocals were brought forward a bit too. So with my Shures, I get the treble extension I want, but because the upper mids are also brought forward, the effect is a bit mixed. Overall there is definitely a treble boost, but how well it suits your phones is dependent on what your phones are capable of and what you are trying to correct, as well as personal preference. For me I felt that the 6TX treble boost goes a bit too low and starts to change the presentation of the upper mids.

    *Digital volume control
    This is a love/hate relationship... I am one who loves mechanical interfaces for their tactile feel and the ability to have visual or physical confirmation of my settings, and this is another reason I liked the old 4G. The good old pot on the 4G gave me an easier way to physically check what my volume level is so I know I am not blasting my ears in a loud environment and keeping my volume at a safe level. An example of this use is when I am on a plane. I try to keep my listening volumes as low as I can comfortably go and try to avoid high levels as I intend on enjoying music for many more ears to come. I know for my 4G, on a particular gain switch position, I can turn the knob with my nail from zero to as far as I can go in one pass (which happens to be just under 1/3 of full movement) and have my source volume at a given position for a listening level I am comfortable with in a quiet environment. I can then know when I am mid-flight, I am not going to be listening above this level and having hours of listening above that level. If I am unsure, its as easy as turning the volume to 0, and then back to the same position in one pass with my nail.

    On the 6TX, the digital volume knob is overall done well. The rate of change is nice and slow which is great for my sensitive phones. It takes about 3 seconds of holding the control to get to my listening level. There are many volume increments so each step is not perceivable. Im making a guess that there are 63 increments from end to end. The small steps mean you don't get stuck between volume levels, however the small steps also make it hard to gauge how far you are from the starting volume unless your keen to do some counting from minimum volume. Time is the main way to roughly measure how much your changing the volume. Time measurement is slightly tricky because there is a small pause before it starts to ramp the volume. I guess this is like how most software based two button volume systems work. When you hold down the button, you initially get a single step change, a pause and then a continuous change in volume, and I suspect thats whats happening here. Based on some rough timing, its about 1 sec delay, and then 6 seconds to go from end to end. The reasoning for this design is so that you can quickly tap the control to change one increment at a time, however because each increment is fairly small, you need to tap 20 times to go from min to 1/3 volume, which is harder to do than to turn an analogue knob.

    Digital volume was primarily to deal with the nature of physical dual potentiometers never being matched at the low volume setting. This is something that is physically difficult to manufacture and therefore it is expected that at low volumes one side will start to have sound before the other. The difference generally applies throughout the whole range, but the perceived difference is greater at lower volumes and at the start of the sweep. My Shures are low impedance phones and are particularly sensitive to this, so on the 4G amp, I had a minimum volume before which both sides were matched. The 6TX digital volume has no such issue! One thing worth noting about the digital volume control is that the minimum volume setting is not full attenuation though, so there is still some sound coming though. Even on the most sensitive Shure phones, with the Gain switch on 0, this is not an issue as it is still well below any usable listening level. Personally, I really like this as I know the amp is working and not in Mute mode and secondarily, it allows me to set the volume to minimum and flick between the Gain switch positions to quickly reach 'known' volume levels.

    Overall, the digital volume control is well engineered and designed. There are plenty of steps for smooth control, a nice slower control speed for safe control of the volume and importantly a nice logarithmic control for a perceived linear volume change. My only usage complaints refer to being able to know where you are with the volume knob, for which the only way is to count the steps from either end. I would love to have a way to know where the volume control is but a display of volume level would be not be easy to implement in this context so for what it is, I think this is pretty much as good as it gets. Well done Robert.

    At Gain position 0, there is a very very low level hiss audible with my sensitive Shures in a quiet environment. At Gain position 1 and especially 2, there is a proportional increase in background hiss, but only really an issue on highly sensitive phones. Practically this is a non issue as the higher gain positions are really only for those who reach the limits of volume control at lower gain switch positions. The older 4G amp had practically no hiss at all gain positions.

    *Things I really liked
    - Tone controls for bass have Level and Frequency adjustment
    - Bass boost has ability to boost lower frequencies only, reducing mid-bass bloat in the boost.
    - Illuminated power switch looks great
    - Same great feeling switches
    - Beautifully engineered case
    - Audio inputs at both ends
    - Well engineered volume control

    *Things I didn't like so much
    - Treble boost - it reached too low and affected the mids a bit too

    *Neutral aspects
    - Getting lost in the digital volume control position. This is the nature of a digital volume, and Robert has done a great job of its implementation, so I put it down to just the way I use it. Perhaps an illuminated volume bar graph, 6 or more small LEDs that show volume position for a few seconds after changing the volume. Question is, where would this go, and what has to go to make room for it.
    - Mute button - I haven't used it much, I can see it being helpful to quickly stop the sound, but I also accidentally activate it and wonder why theres no sound and unplug/replug my cables and check my source for audio output before checking the amps volume. Perhaps a flashing power light can help indicate this mode.
    - I miss having the second headphone output for sharing music with a friend, or a/b testing. This is also not really a big deal at all, since most listening is solo and its probably not ideal to connect two loads on the same output, and a Y splitter does the job, but it was nice to have. This is also something for which I would rather sacrifice for the added switches and controls.

    Overall, I love this amp. The months/years of design and improvement are clearly visible in the works of art that Robert put together and I can see the design decisions that were made on every level of the design reflect someone with a serious attention to detail. Even the screws that hold the amp together look like they received much thought for a reliable yet aesthetic fit and finish.

    *Things I would like to see in the next version
    - A treble boost that doesn't go as low as to change the mids presentation
    - A bass boost frequency option that goes even deeper, to further reduce the effect on mid bass (this is probably only appealing to a sub-bass head like me, and only really useful/applicable on the extended bass boost version too)
    - Flashing power button for mute mode? or something to indicate mute mode
    - A far fetched wish list item but perhaps a led bar graph for volume position. I don't see this being that easy to do, especially if it needs to have enough steps/resolution to be useful.
    - Bluetooth. Not a high quality audio connection, but a convenience thing. Since getting bluetooth headphones, I have found the convenience for listening while commuting without being stuck to multiple devices very liberating. If this amp did bluetooth I could listen to my quality phones and have the amp in my pocket while I could have my phone free in my hand. The bluetooth interface would require another switch, or maybe the power switch would need a third position again, and then finding sufficient internal space for the circuit and antenna isn't going to be easy, not to mention reception issues within a steel case, but it is probably the last thing that would appeal to me. It is something I can see that wont appeal to many others though, but I dont have many good sounding bluetooth options with decent bass extension.

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    Last edited by okwchin; 07-01-2018 at 07:53 PM.

  3. #3
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    May 2016
    Worked find on my computers with OSX, and fine on a Samsung phone. It didn't work on a One+7 but was more to do with the limited compatibility for the phone with USB audio devices. I haven't yet tested with the camera connection kit for my iPhone, and I am unlikely to connect that many adapters as it pushes my boundaries of inconvenience.
    Sound signature and audio quality was no issue as I could not perceive any issues or difference.

    *Mobile interference
    The Alum casing on the 4G meant there was a ear-piercing amounts of radio interference from cellular data transmission from my phone. It was seriously unusable without putting the phone into airplane mode, which is not ideal when I am commuting and using my phone.
    The Steel casing on the 6TX and the amp design significantly reduces this interference with my iPhone 6 plus but is is still very much present. At least its not 4 times louder than my music, perhaps only a third as loud, as the music. Use a lower Gain setting and higher volume position to minimise noise.

    *Cables and Packaging
    The amp came packaged in the signature zip lock bag in a bubble mailer and a small cardboard box.
    The cables included were a 3.5 to 3.5, a USB C to USB micro, USB C to USB C, and USB C to USB A. All of these were around 15-20cm long.
    The USB C to USB A was a particularly nice cable with a grey anodised metal sheathed connector and a nice soft flexible cable with a twisted looking insulation.
    The other two USB C cables were more ordinary with a relatively stiffer insulation. I would have loved to see all the cables have a similar quality to the grey one, which really stood out to me as a much nicer feeling cable.
    The 3.5 to 3.5 was also relatively ordinary, but functional and adequate for this use. Would have loved to have a short right angle interconnect for when I have it tied to my phone.

    *Recommended for;
    - This amp is highly recommended for someone looking for a compact solution with the best bass boost on the market. The built in DAC works well with android phones or computers.
    - The 6TX is great for those who want to take the edge off a hot and sparkly set of phones and want a little treble roll-off.

    I hope to test the 6NX when it is available again and finally give a side by side comparison of the two, a question everyone buying a Headstage amp wants to know!
    Last edited by okwchin; 07-01-2018 at 07:17 PM.

  4. #4
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    Oct 2014
    Great review


  5. #5
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    Oct 2017
    Excellent review. I'd love to see this amp on Amazon so I can my points and save a few.

  6. #6
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    Oct 2014
    Got the 6TX.
    Great as my previous 5TX.

    Thanks Robert

  7. #7
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    Oct 2017
    What is the sound quality vs other similar portable amps like the Fiio E12 or A5 and other a like? I've never seen other review comparisons.

  8. #8
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    Feb 2014
    Quote Originally Posted by Mufasa View Post
    What is the sound quality vs other similar portable amps like the Fiio E12 or A5 and other a like? I've never seen other review comparisons.
    If you only care about sound quality you should check what opamp is used. The opamp is a small electronic chip which defines the sound quality almost completely. So for a great sound quality the praise should go to the manufacturer of those little opamps (mostly Texas Instruments and Analog Devices). As a basic rule a higher price of those opamps results in a more defined sound quality. For the mass market a $2 opamp will be fine. If you are looking for something special then it won't be sufficient. Since 5TX I have decided to go with higher priced opamps as there are many cheap headphone amps available now. Prices can be found on where I source most of my parts.

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