7HZ Sevenhertz 71 USB DAC

TLDR version on YouTube: TDLR - 7Hz 71

The 7Hz 71 is a dongle DAC that seems to have gone fairly unnoticed, at least I hadn’t heard anything about it until I ended up purchasing it out of pure coincidence. I was actually purchasing something else and to meet the free shipping minimum order, I saw it on sale for around 20€ (if I remember correctly) and added it to the cart.

It has sat unopened for quite some time as I sort of forgot about it. I kept seeing it when I was grabbing something else and it wasn’t until this week, when I was grabbing a couple of dongles for a test, that I decided to finally open it and give it a test.

As this was purchased, I am not going to link to any specific store but it seems to be available on all the usual stores, priced around 30€. Its also available on Amazon in some countries and on Aliexpress (although I did see it was more expensive on AE).

Anyways, here are my impressions of this rather budget friendly dongle DAC from the brand who are better known for their IEMs.



Presentation…

The packaging is a simple cardboard sleeve that shows the dongle on the front and a picture of the internal board on the back. There are no specs shown on the packaging, just the brand and model. There is a small logo in the top corner that says “1st - 2022”, but I am not sure what it was actually first in/at.

Removing the sleeve reveals the dongle covered by a transparent plastic sheet and that is about it. There is actually a card inside the box that does show some specs, which are as follows:

DAC: AK4377

THD+N: -108dB/0.0004% (32 Ohms)

1Vrms (32 Ohms)

70mW @32 Ohms

120dB

20Hz-40kHz

PCM 32bit/384kHz

DSD DoP DSD128,DSD64

There's really not much more to say, copying the specs was more of a content filler than anything else



Build and aesthetics…

The dongle isn’t tiny but it is still rather compact, smaller than many other dongles that I have tried out in the past. Completely made of metal, it is not heavy although it does have a little bit of weight to it, giving that sensation of being well built.

Although it is quite simple in it’s build, 7Hz have given it a touch of aesthetics on the face, with a raised center section that features a single, blue, LED (which I have to say is rather bright). The 7Hz logo is shown in white in the center of the raised section, with a sort of robotic shape to the surrounding area.

The cable is fixed, with a 4cm flat section of cable before terminating in a USB-C connector that also shows the 7Hz logo. I am not sure how long the cable will stand up to abuse in a pocket but with it being flat, it allows for it to be bent and attach the dongle to the back of your phone etc.

I honestly have no complaints with the build or aesthetics with this dongle for the price. No, it is not something that stands out as being beautiful but it does have something going on to break up the simple black box.



Functionality…

There really isn’t much I can say here. You plug it into your device and away you go. I have tried it on various systems, Android and Windows, without any issues of it being recognized.

There is no volume control on the dongle, so you will need to be careful when plugging it in to a Windows device, as Windows has the habit of setting these things to full volume (not this dongle but many dongles).

I have to say that the power draw of this device is pretty impressive, being similar to the Apple Dongle in this regard, with the battery of phones not seeming to drop any quicker than if we were using the normal headphone output of the device (for those devices that still have a headphone output).

The dongle does get a little warm after a while but by no means does it get hot. I think if they lost the LED, it would not get warm at all and the battery consumption would be even less.

Just as a note for those of you that care, the 71 does not decode MQA.



Sound…

I have to say that I was expecting less from the 71 when I first plugged it in. I obviously had no idea what it would be like as I had never seen anyone speak about it but I was dubious about a 30€ unbalanced dongle that hadn’t found any fame amongst forums (at least that I have seen).

As I mentioned a moment ago, this dongle uses the AKM AK4377 chip, which has been around for quite some time (info dates back to at least 2018) and has been used in quite a few dongle DAC devices and some compact DAPs (such as the Fiio M5). Some of these devices have received a lot of praise, such as the Lotoo PAW S2, which was released in late 2021 and is still a very popular device today.

I mention this because it is not always about having the latest chip for something to be good, in fact, it's very rarely about the chip, it’s more about the implementation. This is something that I have found with many devices that use what some would consider “old technology” but prove that, when done right, they are capable of achieving a great outcome. I feel that the 7Hz 71 has proved this once again but at a much lower price point.

Ok, this is not exactly a power dongle, I wouldn’t choose it to run my planar headphones, but as an option for IEMs, or even some of my easier to drive over ears, it does a very satisfactory job.

The sound is very neutral, with a hint of coolness but without ever seeming to be harsh or bright. When starting to listen to the 71, I grabbed the IE600 (just because I had them at the side of me) with the custom tips and the result was great. There was nothing about the sound of the IE600 that sounded “off” or “wrong”, with the bass being fast and punchy, and the details shining through as they should with these IEMs.

I tried quite a few of the IEMs I had on hand and the 71 performed well with all of them. If I had to pick a negative one, it would be with the Hifiman Svanar, but even then it is not really a negative, just not quite as good as I am used to it being. I have been listening to the Svanar mostly paired with the M15 but I fell in love with it paired with the Cayin N7 lately and swapping to the 71 just took away some of the beauty of the sound of these IEMs. Obviously neither comparison is fair, as the M15 is a 200€ dongle and the N7 is a 2000€ DAP, and it is not like the differences are in any way suggestive of the price differences, but it was a noticeable step down in the overall presentation of these IEMs (which we need to remember are 60 Ohm with 100dB sensitivity, so it is asking quite a lot from the not so powerful 71).

A set of headphones that I like to use on dongles to give me an idea of performance are the Koss KPH40. These cheap headphones are something I have found to show quite a bit of difference between sources, especially portable ones. They never sound “bad” (and with the 71 this stays true) but I do find that the clarity of bass and the presence of air can change quite a bit. With the 7Hz dongle, I did find that some of that clean punch was lost, with the highs not being quite as open and clear as with other options. By this I don’t mean that there is a huge difference, they are still good sounding headphones powered by the 71, just not as exciting as they are from some other dongle options.



Conclusion…

The 7Hz 71 dongle is a cheap, ultra portable, dongle DAC that has a surprisingly neutral and present sound. I would not really suggest it for over ear headphones, especially those that are not extremely easy to drive, but with IEMs it is a very good performer for very little money.

I have a bunch of dongles (they seem to be breeding) from different manufacturers and at very different price points, and while I wouldn’t say that the 71 has suddenly beaten them all, I would have absolutely no issue using it, much less recommending it.

If you are looking for a very budget friendly dongle and you don’t need balanced (let’s face it, most of us don’t really need balanced), to pair with a decent set of IEMs, then I think the 71 is a great option.

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As always, this review can be found in Spanish both on my blog (www.achoreviews.com) and on YouTube (www.youtube.com/achoreviews)

7Hz 71
Review Date: 03 November 2022


SPECIFICATIONS

DAC: AKM AK4377.
- THD+N: 0.0004%.
- Output Voltage: 1Vrms.
- Output Power: 70mW.
- SINAD: 106dB.
- Frequency Response: 20Hz-40kHz.
- Noise-Floor: <0.9uV.

Supports high-resolution 32-Bit/384kHz PCM and DSD128(DoP) signals.
High-purity 36-core Silver-plated OCC copper cable.
Supports Android 5.1 and above.
Works with iOS devices(Lightning connector to be bought separately).

Test Equipment

IEMs and Earbuds:

1. Etymotic ER4SR (Single BA, 45 Ohm, 96db Sensitivity)
2. Shure KSE1500 (Single Electrostatic 200V, KSA1200 Energizer)
3. SeeAudio Bravery AE (4BA Hybrid)
4. Salnotes Dioko (Single Magnetic Planar)
5. VE Azure (Single DD, 16 Ohm, 105db Sensitivity)
6. VE Monk GO Final

Headphones:

1. FOSTEX T40RP MK3 (Magnetic Planar, 50 Ohm, 91db Sensitivity)
2. VE Pro Supernova (Single DD, 32 Ohm)

Sources:

1. Windows 10, Foobar 2000 (USB 3.0 Power)
2. Sony Xperia 1 iV (HiBy Music, USB Exclusive Mode, Bitperfect)

LISTENING EQUIPMENT USED IMPARTED HUGE INFLUENCE TO SOUND IMPRESSIONS & RATING

Build, Functions, Usability


The first portable DAC/Amp from 7Hz, built on the venerable AK4377 - the exact same one found in Lotoo PAW S1, S2 and Creative SX-Fi. It is an old DAC chip but by no means obsolete.

71 is a simple dongle. The build and packaging quite spartan - intentionally so to keep the price highly affordable. It is very compact, lightweight and highly portable. In fact with the 1 Vrms classification, this 71 can be considered as ultra portable class dongle.

Seemingly made of CNC machined aluminum chassis, 71 comes in no nonsense black powdercoat and adorned with one blue led light that will stay switched on for as long as it is connected to a host. The led itself will not change colors like some other dongles depending on the resolution of the media being played.

The digital USB connection is not detachable, it has a permanent simple ribbon type cable which 7Hz mentioned to be made of SPC strands, and I believe it is also well shielded as proven by 71 ability to resist RF interferences really well when used portably with my phones. In view of this, I do not lament too much on the lack of ability to switch USB cables (normally it would have been USB C mini connectors on dongle side)

Perhaps the most impressive aspect of 71 build is the efficiency of power draw to portable hosts. I subjected my 71 to continuous play on my Xiaomi Mi 9T (4000 mAH Battery), running on HiBy USB Exclusive mode at normal listening level.
71 was able to score a very respectable 12-13 hours of playtime until the battery shows 2% remaining. This is rather impressive. In comparison, dongles like Cayin RU6 and Lotoo PAW S1 scored average 10-11 hours.
Additionally, 71 managed to keep the temperature in check. Just mild hint of warmth that doesn't cause for any concerns.

Sound Impressions

71 is a truthfully neutral and natural sounding DAC/Amp. I am very familiar with AKM based dongles and I must say I am impressed with the tuning to keep it accurate and realistic. The hallmark of a great DAC/Amp has always been their ability to render uncolored output - of which will work well with any pairing partners to reflect on their own sound signature. For example, I always start listening to new dongles with Etymotic ER4SR - an IEM that is widely regarded as a reference for true neutrality. ER4SR would immediately detect any coloration if they are evident in the output - what I heard from this combo convinced me, that 71 does not impart any sort of boosting in any of the frequency ranges. And that is a huge plus in my book.

Dynamic wise, the transients of 71 can be considered as highly mature and polished - as expected from well implemented AKM DACs. The vibrancy level is energetic enough without any unnatural sense of euphony. In fact, drawing comparisons from Lotoo PAW S1 and S2, I would say 71 exhibited a bit more of energy and focused more on crispness - while the S1 & S2 remained as the smoothest (yet still crispy) dongle to exists still. From my perspective, the dynamic temperament of 71 seems to be bridging the gap between Lotoo PAW S1/S2 and Creative SX-Fi - of which the tuning of SX-Fi exhibited even more energy (SX-Fi almost sounding like ESS Sabre type of dynamic characteristics). Still on the same subject, dynamic range of 71 is surprisingly good for a 1 Vrms dongle. When paired with Shure KSE1500 and Fostex T40RP MK3, I am hearing great reach of depth on either ends of the sound spectrum. Micro dynamics audibly heard and present, indicating good extensions on both ends. Well perhaps not as pronounced on T40RP MK3, but the nuances are there subtly.

Tonal and timbre balance for 71 is admirably organic, almost analogue - but not quite as analogue sounding from the likes of CEntrance DACport HD or Ovidius B1 (both being the very best of AKM based dongles still). Notably I can hear 71 just lacking some element of air, the sense velvety organic and realistic tone is there, yet slightly masked by the preference for more crispy timbre deposition. But one thing for sure, 71 has excellent Pinna control than many other ESS or Cirrus Logic dongles - of which most of them would sound digital and edgy - but not 71. 71 offers crisp polished presentation. The pitfall of some AKM tuning, they also tend to sound dull edged and seemingly lacking resolution, but 71 does not exhibit this trait. The tone, the timbre embodies solid natural sound that is crisp and well rounded.

Being a neutral DAC/Amp, 71 is exhibit consistent presentation for Mids, Lows and Highs. As noted earlier, I hear no element of boosting in any of those areas. It will then boil down to the nature of the paired partners to develop sound synergy. Pair it to a bassy unit, 71 will not fail to act accordingly and present strong Bass performances - at least for anything that's not too demanding in term of power. At least up to 50 Ohm, 71 Bass sounded fast, textured and well extended - being neutral means that 71 will not add any boosting to impart additional impact, slam and presence beyond the paired partners ability. The Mids being solid with realistic attack and tonality. The highs exhibiting accurate sparkle and shimmer, with Treble details presented depending on how competent the partners are (which also means 71 will not boost any partners that are already weak with Treble). Treble attack and decays being realistic and organic, never any hint of being metallic or dry even when paired with natively bright sounding partners.

Technical wise, 71 is a highly competent dongle. The most prominent element that caught my attention from the get go was how spacious and wide the headstage is - perceived soundstage for IEMs appeared generous with width and depth.
Then the speed, the manner how agile and efficient 71 is with resolving either highly complex or fast music without sounding sluggish or muddy. On this element 71 is quite capable to tighten up slow sounding IEMs to make them less syrupy or outright bloated - simply amazing. 71 is also very good with overall resolution and transparency, the output is quite faithful to the intended sound as per contained in the sources - Macro and Micro details audibly heard and present. There was never a moment anything felt lacking. In alignment with the spacious headstage, 71 also offer crisp imaging with good spatial positioning, tracking different notes was effortless especially on highly resolving partners.

Driving Power

Despite being rated at 1 Vrms, I am truly surprised that it was able to drive my 50 Ohm, 91db Magnetic Planar of Fostex T40RP MK3. Yes I will need to crank up the volume to get proper listening loudness, and when this is achieved, the sound was in fact wholesome and engaging.

To show some perspective of 71 power, as compared with my favorite dongles:
- Ovidius B1 - 30/100 Volume
- Centrance DACport HD - 34/100 Volume
- 7Hz 71 - 58/100 Volume
- All tests on USB 3.0 900mA Power, Windows 10

Upon closer scrutiny and comparison, I will admit that both Ovidius B1 and DACport HD has upper hand. Especially with the density of dynamic transients which are richer - Bass and Lower Mids being more potent - while 71 appeared leaner and lacking utmost density. However this is only evident when doing side by side comparisons. Otherwise on its own I would say that I can be satisfied with 71 driving my stubborn planars for casual listening. The most important part being, 71 does not exhibit any worrying negative effects subjected to driving heavy load, no hint of crackling or distortion as would be observed from less capable, weaker DAC/Amp dongles. 71 does not sound distant or meek, not at all.

Ultimately, I believe the optimization for 71 is for driving highly efficient IEMs. With the craze on IEMs these days. New ones being released almost everyday - and each of them for the most part are highly sensitive. Regularly, I used my 71 paired with SeeAudio Bravery AE, VE Azure and Salnotes Dioko. The synergy exhibited by 71 to those IEMs being great and fluid. Another important element, 71 also offer very clean and black background with these highly sensitive IEMs, especially hybrids like Bravery AE which are so prone to picking up floor noises.



FINAL WORDS

7Hz 71 is a great sounding dongle - the simple fact. Being highly neutral, resolving and articulate with technicalities, making it such an amazing bang for the buck device. 71 has amazing versatility to pair with any type of partners, especially for those highly efficient IEMs. While at it, 71 does not slack with more demanding pairing, it has ample juice to not sound outright meek and sketchy. But yes, perhaps best to keep it with those under 50 Ohm or with over 100 dB of sensitivity - and then the output would be 100%. Not forgetting how efficient it is with power draw from portable hosts - and keeping sensible with not getting hot, or RF interferences.

71 does some Cons here and there, subjectively I don't see the Cons being detriment to the overall value proposition. The non removable cable or advanced features, or lack of independent volume adjuster - those are highly negligible Cons considering how affordable this unit is - with great sonic performances on top of it and the cable itself has proven to be quite robust for my own daily usage. I can be quite abusive with my audio gears, but 71 seems to withstand all those admirably.

Ultimately, 7Hz 71 is something I would not hesitate to recommend - especially for anything below $40.




Best Pairing: Highly flexible and adaptable to most IEMs & Headphones
#donglemadness

7Hz 71 is available at HiFiGo:
https://hifigo.com/products/7hz-sevenhertz-71