Last year a new company called Audinst made waves with their HUD-mx1 compact USB DAC/headphone amp product. Operating out of Korea, Audinst impressed many people with their initial offering. Since then the little mx1 has become a common recommendation around here as a very solid entry level all in one device. Back in April of last year, I was on track to be the first person to post a detailed review of the HUD-mx1. After posting it, I learned that another user named audiofil beat me by about 8 hours. His review was very well done, and other positive reviews by others soon followed.
Ever since that time, the Audinst website has had little “preview” sections for some upcoming products: The AMP-HP portable headphone amp, the AMP-mx1 digital power amp, and the HUD-mini USB DAC/headphone amp. Last month the AMP-HP was released so I decided to check it out. Hopefully I can get this posted in time for it to be exclusive.
Maybe it’s my imagination, but I could have sworn that this forum had much more interest in portable amps a few years ago. It seemed like Ray Samuels and iBasso were releasing a new model every few months, and there were tons of other small and medium sized players in the market. Skylab did a huge roundup/comparison of portables starting in early 2007 and continuing for several years until there were over 50 models represented. Looking at the list now, many of those companies no longer even exist. Of those that do, only a handful still actively make portable amps. Clearly the market has shifted. Despite that, there remains a need for good quality portables at reasonable prices. Surely the demand is large enough to support more than just a few models each from iBasso and Ray Samuels. Audinst seems to agree.
I think they meant designed in Korea, but we get the idea
The AMP-HP does not break any new ground in terms of design. I don’t know if such a thing is even possible at this stage - everything that seemingly could be done already has. The AMP-HP is just a basic smaller sized portable with a standard 1/8th inch headphone jack. There is no balanced option, no built in DAC, no cross-feed circuit or bass boost, just good performance with no frills.
The case measures 80mm x 60mm x 20mm, which is on the small side as far as portables go. This is not quite what I’d consider an ultra compact amp though. One look at the pictures shows that the AMP-HP has a slightly unusual shape; one side has a protrusion that I like to call “the hump”. This “hump” keeps the amp from being very thin, and it makes it require a certain orientation when pairing with a DAP. The other side is flat so it still works fine. As I tried to capture in my pictures, the “hump” was necessary to provide clearance for some of the internal components.
The case is made from lightweight but sturdy aluminum. The main body is silver and the ends are black, which is an inversion of the color scheme seen on the HUD-mx1. The rear panel houses a 1/8th inch input and the jack for plugging in the charger. On front we find the 1/8th inch headphone output, a volume knob, and a power switch. Audinst implemented a feature that I find handy – to get power, it requires the switch to be in the “on” position AND a plug inserted in the rear input jack. Without both of those happening there is no power. This means that when I unplug it and set it on the shelf for the night, but forget to slide off the power switch, it won’t be dead by the time I use it again. A small thing, but very handy.
Inside we find lots of components packed into the small case. One side has all SMD parts including the Analog Devices AD8397 opamp which is used in the output stage. The other side has some relatively large capacitors (thus the need for the case hump), an Alps branded potentiometer, a socketed opamp, and a spot for the NiMH battery. The stock opamp is a Muses 8820 from New Japan Radio Company. This bipolar-input dual opamp seems to have been released last year and I don’t recall seeing it used anywhere else. Since it is socketed, the user is free to swap in different opamps to see how it affects the sound, just like the HUD-mx1. Unfortunately I was unable to get an answer from Audinst as far as which opamps might be good to try. I know the results would be personal preference but a list of safe options or even a range of required specs would be helpful.
The battery is “Audinst” branded and lists a 800mAh/3.6V rating. They claim a 2-3 hours charge time and roughly 10 hours play time, which is rather low in comparison to some other portables. I could have sworn that I was getting more than that – I was thinking more like 12-14 hours. That could be due to my use of sensitive IEMs for much of the listening time, which don’t require much power to reach high volumes. But realistically I don’t ever let it die completely. Once a week I plug it in for a few hours and that is enough to keep it running. If only my cell phone had a similar capacity.
As far as power output, Audinst is rather vague on the specs. They list a peak output of 300mW per channel at 32 ohms. That’s great, but I wanted to know more. When I asked, this is the reply I got:
Each headphone impedance and the driving force differs,
HUD-mx1 driving high impedance headphones to use with no discomfort and
designed to maintain clarity so, when you turn up the volume without distortion.
When Normal 16 ~ 32 ohm headphones to use the appropriate volume music playing,
device's output normally about 5mW ~ 10mW ,
a very large volume listening, or hearing is not good
then turn up the volume to hear, even if the output is about 20mW.
When 32ohm Impedance headphones are connected,
The output of 300mW
it is just equipment provided by the max spec,
The headphones use a properly adjusted according to volume.
so, ouput figure According to impedance is not meaningful.
First off we need to excuse the language difference. I think the English is good enough to get the point across. Secondly, they accidentally said “HUD-mx1” instead of “AMP-HP”. Not a big deal. But the message of the reply is interesting. You could take it different ways: One would be to take it at face value. I think it is true that we often grossly overestimate how much power is needed to drive most headphones. They could basically be saying that they aren’t interested in trying to wow people with meaningless specs. That’s a good thing. Obviously you could take their statement another way, and assume that they are hiding something or that the amp doesn’t perform as well into other loads. That’s something you will have to decide for yourself. One spec that other companies don’t always give but Audinst does is the output impedance. They list it as 5 ohms, which is low enough to avoid interaction with all the headphones I can think of. Some amps have a much higher output impedance, which can lead to unpredictable results with low impedance headphones. Since this amp will likely often be used with IEMs ranging from 16 ohms to 50 ohms or so, the low output impedance is a good thing.
This is why the "hump" is required for clearance:
The AMP-HP feels like a pretty solid device from a build quality standpoint. The case is not overwhelmingly nice but I’d call it “pretty good”. When I first received it, the jacks for both input and output were on the tight side – I had to exert more effort than usual to get a plug in or out. After using it for a while they have settled down and are normal. The volume control was similar – it was nice and smooth but turned harder than I would have liked. After a week or so it loosened up a bit and has remained the same ever since. The power slider doesn’t look as cool as a switch or button, but is actually quite functional. I’ve had less accidental activations/deactivations with it than I’ve had with other portables.
The HUD-mx1 came in a nice retail looking box and the AMP-HP is very similar. They both even take design cues from the products themselves, which I thought was a nice touch. Audinst has packed the AMP-HP box with a fairly generous helping of accessories. You get the amp itself, a user manual, a basic short mini to mini cable, a basic iPod line-out dock cable, a storage pouch, a wall wart charger, and a set of stick-on rubber feet. That’s a lot of stuff for a fairly low priced device. When I say basic for the cables, I mean that they are just plain white cables. No fancy braided copper or anything like that, but they get the job done. My only issue is that they seem a bit too long for portable use. But I’ll take imperfect accessories any day over nothing at all.
This is the equipment I used to evaluate the Audinst AMP-HP:
Source: Sansa Fuze, Sansa Clip+, QLS QA350, iPod (5.5g Rockboxed)
Headphones: Unique Melody Merlin, Kozee Infinity X1, Westone AC2, Monster Turbine Pro Copper, Sennheiser HD600
In addition, I used the Audinst HUD-mx1 as a DAC in order to compare the AMP-HP to the headphone section in the mx1.
I let it burn in for several hundred hours before ever listening to it, just in case burn-in is a real thing.
My initial impression of the AMP-HP was that it didn’t have much character. That sounds like a negative thing, but it is actually a compliment. Unless you have some very specific need such as an anemic headphone that needs a bass boost or a bright headphone that needs to be tamed, you generally want an amp to be as neutral and transparent as possible. That enables it to be a good all purpose performer. The AMP-HP did seem to fit that description, and I wasn’t picking up any notable weaknesses either.
Highs seem nice and clear. There is a good amount of detail on display without routinely going overboard to become bright. I do notice just a hint of what I’ll call “sheen” in a few instances. These are mostly on tracks that were borderline anyway – it seems that the AMP-HP is not the type to cover up a major flaw. That being said, it does a very good job in most cases of presenting the material in an accurate way, and for the most part is very enjoyable. But there is no doubt that this amp favors high quality recordings.
Mids are nice and accurate. No lushness or artificial sweeteners here, just nice transparent reproduction. Female vocals sound especially good – such diverse acts as Fleetwood Mac, Blondie, The Cranberries, Jacintha, A Fine Frenzy, and Patti Smith are all very enjoyable, despite being vastly different in style and recording quality. Not to take anything away from male vocals; they sounded great but just didn’t stand out as much as the ladies. In general the AMP-HP has a fairly open sounding presentation, and the good sense of balance translates to broad compatibility will all types of music.
Lows are a particular strong point of this amp. After extended listening I think I notice just a touch of added warmth down deep, which keeps this from being a completely neutral amp. I wouldn’t call it a significant bass boost, and it may just be a byproduct of the excellent bass quality, but it makes for a fun listen. In my experience you have to climb very high up the portable headphone ladder to get bass performance this good. The Leckerton UHA-6S had it, and the iQube might even be better, but those cost a good deal more (in the case of the iQube, significantly so).
The AMP-HP has a nice open sound, with an accurate soundstage that has adequate width but surprising depth. I never felt like it was holding me back, even when partnered with IEMs costing over 5 times its price. There is absolutely nothing “budget” about this aspect of the sound, nor any other aspect for that matter.
As far as power goes, the AMP-HP seems to have as much as I could possibly want or need. Maybe Audinst was right when they downplayed the specs, because I really see no need to know the specifics… Every model of headphone that I would reasonably want to carry around with me is easily powered by this amp. Even my decidedly non-portable 250 ohm Beyerdynamic DT880 and 300 ohm Sennheisers HD600s do well enough – as well as can be expected from a compact battery powered amp that is. Some people do seem to have crazy ideas like powering the orthodynamic HiFiMan HE-4s with a portable amp. In that case, I suspect the little Audinst would not be up to the task. But with reasonable expectations it should be fine.
The only other portables I have around these days are low budget models: the TCG T-Box that I acquired fairly recently, and the Vivid Technologies V1 which I’ve had for a while.
In comparison to the Vivid, the Audinst seems more transparent and neutral. The V1 is more forward and aggressive. Once again I love the pairing of V1 and Sennheiser HD650, but aside from that I prefer the Audinst the rest of the time. It just has a less colored sound signature that works across a wider range of headphones as well as genres of music.
The TCG T-Box is a great little budget amp. It is similar in size, actually a bit smaller than the AMP-HP, but that’s where the similarities end – these two amps sound fairly different. The AMP-HP deviates from neutral just a bit by having a slight smiley face curve. Bass is a bit warmer and highs are ever so slightly tipped up. The T-Box is the opposite, focusing on the midrange. We could call it an “n” shaped curve, or a frowny face. Neither is a huge coloration, but when you spend time to get to know each amp, the differences become clear. The T-Box has extreme battery life, while the AMP-HP is merely acceptable. The AMP-HP has more power on tap for driving full sized headphones. Ultimately the TCG is more practical: smaller size, longer battery life, lower price. But on pure sound, the Audinst takes the win.
Lastly, I compared the AMP-HP to the built in headphone amp section of the HUD-mx1. Switching back and forth, I found that both have a very similar overall sound to them. The mx1 amp seems to have more power on tap and can even drive 600 ohm headphones pretty well. The AMP-HP prefers 300 ohm or lower models. Using a good IEM like the UM Merlin reveals that the portable has a slight edge in terms of fine detail retrieval. The slightly warm bottom end is generally welcome over the more flat mx1, and the highs seem particularly better resolved. But these differences are small. Both of these units use the same AD8397 which may account for the similarities.
With their debut product, Audinst had a solid hit on their hands. The AMP-HP is their second release, and I’m fairly impressed with it as well. It has a great sound to it – warm, clear, smooth, and detailed. I like the fact that its value doesn’t rest purely on the sound; we also get great build quality, a generous package filled with useful accessories , and a design that is pleasing to the eye. All of this comes at a price that should be easy to swallow for most people.
There is a lot to like about this amp. The only complaints I can think of are fairly minor – battery life could be a bit better, and the “hump” design is controversial. If you can get past those, the AMP-HP may be a perfect match for you.
As I mentioned earlier, the portable amp market doesn’t seem to be what it once was. We still have plenty of action on the very low priced end of things, and the higher end seems well represented too. But I don’t see as many mid-priced offerings being released these days. The AMP-HP is a solid entry into that category, and I’m glad that Audinst took their time in making it this good. There are a few other interesting choices out there at the moment – the new iBasso D-Zero and the Leckerton UHA-4 come to mind. But I haven’t heard those so I will refrain from comparisons. Based on what I have heard, I can’t think of another model at this price that I would recommend more highly.
Edited by project86 - 8/20/11 at 1:59pm