7HZ Sevenhertz 71 USB DAC AMP

Author：Andy.EF

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 temperament instead). 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