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发表于 2019-8-8 14:06:07 | 显示全部楼层 |阅读模式

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Benchmark HPA4

设计用于匹配其紧凑型DAC,Benchmark的全模拟耳机放大器
采用相同的THX‘消色差’技术,在其100W的AHB2功率放大器中首次亮相。

审查:安德鲁·埃沃德实验室:保罗·米勒

随着耳机收听的蓬勃发展,甚至超过了新转盘的普及,高保真的前景在很大程度上发生了变化。不仅是高保真节目在个人听力体验上引起了关注,而且专用的耳机事件也以自己的方式发展起来。硬件也在变化:市场上充斥着DAC/耳机AMP组合,从微型(和高度便携)AudioQuest蜻蜓模型[HFN 10月16日],到“可移动”和弦雨果2[HFN 8月18日],以及电源供电的设备,如IFI音频专业IDSD[HFN 9月18日]。“18”。可以说,与卢克曼的P-750U(HFN 9月18日)的前景更为接近,基准的HPA4也不是上述任何一种。无论是银色还是黑色,在英国售价为3295英镑,它没有内置的数字到模拟转换,因此,就像鲁克曼的豪华重量级耳机一样,它只是一个全模拟的耳机放大器。好吧,当我说“仅仅”时,我会对HPA4造成损害,因为我什么都没有。关于它。事实基准将其产品描述为“具有中继增益和输入控制功能的参考立体声耳机放大器和参考线放大器”,这可以让您了解这里的情况,但仅暗示这实际上是两个完全独立的产品包D组成一个相对紧凑的单元。

双重作用
小尺寸——只有22厘米宽,没有太深,10厘米高以下的嗅嗅——考虑到同样小,但如此强大的AHB2功率放大器也来自纽约锡拉丘兹公司[HFN 3月15日]。更不寻常的是,与大多数能够作为前置放大器加倍的耳机放大器不同,这一个放大器不会在耳机插座和前置放大器之间分离输出,但实际上具有两种功能的离散放大器部分。耳机部分由THX的功率放大器供电,采用与公司在其AHB2中首次使用的相同的AAA(消色差音频放大器)技术(见PM的Boxout,第71页)。此外,Benchmark的线路放大器使用继电器进行输入选择、增益控制和静音,而四个独立的256步衰减器(带有镀金触点)则夸口“流畅的音量变化”。其中两个衰减器为耳机输出供电,两个为前置放大器输出供电。正如PM在他的实验室报告[P73]中指出的那样,这种设计不仅给了HPA4出色的性能,而且也给人留下了深刻的印象,至少可以说是信号传递,无论是进入耳机还是外部电源放大器。确认。有一个标准的6.35毫米立体声或四针平衡卡侬连接耳机的选择,而放大器有选择的RCA和平衡卡侬前置放大器输出加上,不同寻常的是,一个总结单平衡输出,可以用来驱动一个合适的超低音,例如,输入是provid每台平衡XLR和RCA音箱配备两套,还有一对12V触发连接,允许打开和关闭远程放大器。彩色触摸屏允许调整这些功能,以及输入命名、设置音量偏移(即每个输入的相对电平和前置放大器和耳机输出的单独电平)等细节。还可以将基准DAC的操作与HPA4集成起来,使两者作为一个单元工作,两个单元都用同一个遥控手机操作。尽管触摸屏显然与HPA4的所有类似的简单性不一致,但它只增加了用户的吸引力,尽管如果你不分享我的视图,你可以调暗显示,并设置它关闭一个设置周期后,你最后一次触摸它。这既保证了设备的灵活性,又保证了设备的简单使用。你甚至可以锁定设置,如果你和一个很可能玩弄的人分享你的生活-或者如果你无法抗拒诱惑自己!

音乐生活
在没有明显的功率放大器合作伙伴(3095英镑的AHB2)的情况下,我投入服务,投入使用了紧凑型5010单块(见第66页),而来源包括我通常使用的NAIM NDS/555PS,通过传统电缆连接到HPA4,以及优秀的先锋PD-70AE“全做”播放器[HFN May'18]通过其平衡输出。我还试验了基准HPA4和曝光5010之间的单端和平衡连接,以及和弦公司和QED的所有电缆,而扬声器是我的常驻PMC OB1和Neat's Iota Explorer[HFN Jul'18]。我有一系列的尝试,包括Quad Era-1[HFN Aug'18]、B&W公司的P9签名[HFN Mar'17]、一对使用良好的Focus's Spirit Professional[HFN Dec'15]和Oppo PM-1[HFN Jul'14]我发现自己经常回到这里,最后这些也让我在两个会议中都可以尝试HPA4。常规和平衡模式。hpa4和ifi audio pro idsd(通过比较现有)都声称具有相同的定义、低噪音和宽范围驱动能力的声波属性,但很难不承认ifi audio的型号将hpa4的性能降低了25%,并带来了非常好的ds。作为交易的一部分,具有D功能的DAC。很明显,基准测试将以任何一种从头到脚的方式开始,一只手绑在背后,至少在你花点时间听所有类似的竞争者之前,这是一种印象。所有的一两首曲目都应该做到这一点,无论是像oppo PM-1这样的耳机还是作为前置放大器使用,hpa4都能以其播放音乐的方式带来纯粹的冲击、开放性和生动性。我播放了一段新的经典频道录音,钢琴家安娜·费多洛娃的四个幻想曲(ccs 41318;dsd 256),并立即被它的生命方式所震撼,演奏的每一个元素和斯坦威的大小都在一个可靠的音乐厅声学中,很容易展示出来。

物质的热量
在过去的十年中,在开发高效(冷运行)放大器技术,避免“冷”(零偏差)B级输出级引起的服务交叉失真方面,花费了大量的工程努力,同时在声学方面与最好的“传统”A级进行竞争。和A/B设计[见调查,2015年2月HFN]。D类放大器是一种解决方案——将音频信号表示为一系列非常高频的脉冲——它们在负载容限、响应平坦度、低噪声和失真方面有了飞跃性的改进。备选方案包括H类,这是美国对欧洲G类的指定。这些设备采用两个或多个PSU轨道,每个轨道的电压较高,始终选择最低的电压以适应主要信号。因此,输出级的过度耗散被最小化,效率得到提高。对于其HPA4中的耳机放大器,Benchmark使用了THX的“H级消色差音频放大器”(THX AAA)技术,进一步改进了使用两对或多对增加的直流轨道的产品。电压。然而,在这里,任何轨道开关故障或交叉失真,在其最终的B类输出阶段,很大程度上消除了前馈误差校正。当然,最高的“绿色”效率对于输出有限的交流供电耳机放大器并不重要,而且所使用的特定THX AAA-888模块仍然有几瓦的静态(闲置)消耗。在实践中,基准是使用THX AAA技术的基础上的性能,所以hpa4仍然运行相当温暖!颗粒物

大气中的ace
这是一个真正的“室内表演者”的经历,我立刻回到了我花时间监控录音的时间,因为它是在7月份的Eindhoven Muziekgebouw制作的。然后,通过生产商/工程师贾里德·萨克斯(JaredSacks)的备用AKG K1000“耳麦”,其效果是脊柱刺痛。通过由hpa4以平衡模式驱动的oppo PM-1听[来自nativedsd.com]的发行版,感觉有点情绪化,就像费多洛娃以惊人的速度、精神和精度攻击贝多芬的《月光》奏鸣曲的最后一段一样令人满意。在汤姆·琼斯(Tom Jones)2010年的专辑《赞美与责备》(Island 274 129-7)中,内斯也有很多证据,强大的乐队以卓越的影响力解决了问题,但最重要的是,他特写了这一非凡声音的特写镜头,尤其是在开场白“我有什么好处?”“还有罗塞塔·瑟普修女的‘奇怪的东西’或者砰砰的‘燃烧的地狱’。这张专辑可能是一个著名的被唱片公司老板视为“病态笑话”而忽略的预售专辑,但听琼斯通过设备给予歌曲完全的承诺,就如同这张专辑揭示了评价的范围有多广一样——这张专辑的声音充满了氛围和真诚。

就在轨道上
从技术上讲,这里的声音和你想听到的一样完美,但HPA4真正的美在于它让表演者、制片人和工程师的所有意图得以实现。播放最近发行的一个平缓的动态,如Nicki Minaj的王后专辑[年轻的钱/现金钱/共和国00602567712183]和所有的傲慢和态度,据说在那里,它听起来很乏味。但是,换成比尔·弗里塞尔和托马斯·摩根的现场小城镇场景(ECM 2525),所有的现场、氛围和乐器音色都会立即恢复。所以,是的,这不是一个用来美化糟糕录音的序言,也不是给源组件一个简单的时间,但要正确,它可以以一种避开许多更昂贵前置放大器的方式开启魔法,更不用说一个加倍的优秀耳机放大器了。它喜欢声音和真实的乐器,能让它发光,正如洛伦娜·麦肯尼特最近的《迷失的灵魂》专辑《奎宁路QRCD117》中所清楚的那样,这张专辑绝对会发光,或者更大气的光线,比利·布拉格和乔·亨利的《伟大的美国人》现场录音。铁路[烹饪乙烯基库克CD623],在那里环境影响对这些地点的记录往往是相当惊人的字面意义上-特别是通过耳机!铁路站台的声音和声音在背景中消失了,增加了现场的氛围,甚至还有一条“室内”轨道,“等待火车”(记录在罗伯特·约翰逊第一次参加会议的同一个圣安东尼奥酒店房间里),具有可爱的复古氛围和亲密感。HPA4当然可以摇摆不定,当它达到输出水平时,其惊人的能力意味着它可以提供尽可能多的功率放大器或手机可以承受。事实上,如果没有声音改变一个IOTA,声音会变得更大,因此如果不将合作组件驱动到它们的极限,就要注意一些。但这也证明了这款非凡产品的纯净度和熟练设计。

高保真新闻裁决
尽管首相幽默地注意到了这一点,但功率放大器的破坏或是耳朵的撞击并不是基准的HPA4的全部。相反,它的好处在于它对你的系统没有任何限制:任何可以听见的故障都需要在其他地方寻找。是的,这是一个比你的普通耳机放大器稍微复杂一点的购买,它的全模拟设计意味着大多数将需要一个合作的DAC,但声音是无可置疑的。


左图:HPA4是“半宽”,只有一个音量控制;有6.35毫米和平衡的卡侬耳机插孔,触摸屏进入设置菜单。
右图:这里使用四个独立的256步继电器开关衰减器,每个衰减器两个用于立体声耳机和线路输出[左上角]。此和THX AAA-888耳机放大器[右上角]由开关PSU[下角]供电。
上图:这里没有数字输入…HPA4是纯“模拟”的,在XLR上有两个平衡输入,在XLR和RCA(INC MONO)上有两个单端(RCA)和线路输出。
左图:Benchmark坚固的小遥控器关闭输入选择、音量、静音和显示亮度





Lumin U1>Sonnet Mopheus>Boulder810>UA Boulder MK3/
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 楼主| 发表于 2019-8-8 14:07:22 | 显示全部楼层
With the boom in headphone listening outpacing even the uptake of new turntables, the hi-fi landscape has changed to a significant extent. Not only are hi-fi shows shining a spotlight on the personal listening experience but dedicated headphone events have spun out in their own right. And the hardware is changing, too: the market is awash with DAC/headphone amp combos, all the way from the tiny (and highly portable) AudioQuest DragonFly models [HFN Oct ’16], to the ‘transportable’ Chord Hugo 2 [HFN Aug ’18] and mains-powered units such as the iFi Audio Pro iDSD [HFN Sep ’18].Arguably closer in outlook to Luxman’s P-750u [HFN Sep ’18], Benchmark’s HPA4 is none of the above. Available in either silver or black finishes and selling for £3295 here in the UK, it has no built-in digital-to-analogue conversion and so, like Luxman’s luxury heavyweight, is merely an all-analogue headphone amp.Well, when I say ‘merely’ I do the HPA4 a disservice, as there’s nothing mere about it. The fact Benchmark describes its product as a ‘Reference Stereo Headphone Amplifier and Reference Line Amplifier with Relay Gain and Input Control’, which should give you some idea of what’s going on here, but only hints at the fact that this is actually two completely separate products packed into one relatively compact unit.

DOUBLE ACT

The diminutive dimensions – it’s just 22cm wide, not much deeper and a sniff under 10cm tall – should come as no surprise given the similarly small, but ever-so-mighty AHB2 power amp also from the Syracuse, NY, company [HFN Mar ’15]. What’s more unusual is that, unlike most headphone amps able to double as a preamp, this one doesn’t split its output between headphone sockets and preouts, but actually has discrete amplifier sections for the two functions. The headphone section is powered by a power amp from THX, employing the same AAA (Achromatic Audio Amplifier) technology first used by the company in its AHB2 [see PM’s boxout, p71]. Alongside, Benchmark’s line amplifier uses relays for input selection, gain control and muting while four independent 256-step attenuators, with gold-plated contacts, boast ‘silky smooth volume changes’. Two of these attenuators feed the headphone outputs and two service the preamp outputs.As PM notes in his Lab Report [p73], this design gives the HPA4 not only outstanding performance, but also rather impressive – to say the least – signal delivery, whether into headphones or external power amplification. There’s a choice of a standard 6.35mm stereo or four-pin balanced XLR connections for headphones, while the amplifier has a choice of RCA and balanced XLR preamp outputs plus, unusually, a summed mono balanced output, which could be used to drive a suitable subwoofer, for example.Inputs are provided on two sets apiece of balanced XLRs and RCA phonos, and there’s also a pair of 12V trigger connections to allow remote amplifiers to be switched on and off. The colour touchscreen allows the function of these to be adjusted, along with niceties such as input naming, setting volume offsets (ie, the relative levels of each input and separate levels for the preamp and headphone outputs) and so on. It’s also possible to integrate the operation of a Benchmark DAC with the HPA4, allowing the two to work as a single unit, both operated with the same remote handset.That touchscreen, although apparently at odds with the all-analogue simplicity of the HPA4, only adds to its user-appeal, though if you don’t share my view you can dim the display, and indeed set it to turn off a set period after you last touched it. This ensures the flexibility of the unit while also keeping things simple in use. You can even lock out the settings should you share your life with someone likely to fiddle – or if you are unable to resist the temptation yourself!



RIGHT: Four independent 256-step relay-switched attenuators are used here, two each for the stereo headphone and line outputs [top left]. This and the THX AAA-888 headphone amp [top right] are fed from a switching PSU [bottom]



LIFE IN MUSIC


In the absence of the obvious power amp partner, the £3095 AHB2, I pressed into service the punchy Exposure 5010 monoblocks [see p66] while sources included my usual Naim NDS/555PS, connected to the HPA4 via conventional cables, and the excellent Pioneer PD-70AE ‘do it all’ player [HFN May ’18] via its balanced outputs. I also experimented with both single-ended and balanced connections between the Benchmark HPA4 and the Exposure 5010s, with all cabling from the Chord Company and QED, while the speakers were my resident PMC OB1s and Neat’s Iota Xplorer [HFN Jul ’18].Headphones? I had a range to try, including the Quad ERA-1 [HFN Aug ’18], B&W’s P9 Signature [HFN Mar ’17], a well-used pair of Focal’s Spirit Professional [HFN Dec ’15], and the Oppo PM-1 [HFN Jul ’14] to which I find myself returning often, these last also allowing me to try the HPA4 in both conventional and balanced modes. Both the HPA4 and the iFi Audio Pro iDSD (on hand by way of comparison) claim the same kind of sonic attributes of definition, low noise and wide-ranging drive capabilities, but it’s hard not to acknowledge that iFi Audio’s model undercuts the HPA4 by a healthy 25%, and throws in a very good DSD-capable DAC as part of the deal. Clearly Benchmark would be starting any kind of head-to-head with one hand tied behind its back.At least, that’s the impression until you spend some time listening to the all-analogue contender. All of a track or two should do the trick, as whether with revealing headphones such as the Oppo PM-1s or used as a preamp, the HPA4 simply drops jaws with the sheer impact, openness and vivacity of the way it plays music. I played a new Channel Classics recording, pianist Anna Fedorova’s Four Fantasies [CCS 41318; DSD 256], and was instantly struck by the way it sprang to life, with every element of the playing, and the size of the Steinway in a credible concert-hall acoustic, readily on display.



LEFT: The HPA4 is ‘half width’, with a single control for volume; there are 6.35mm and balanced XLR headphone sockets, and the touchscreen accesses the set-up menu


THE HEAT OF THE MATTER

The past decade has seen a lot of engineering effort expended on developing efficient (cool-running) amplifier technologies, avoiding the sev ere crossover distortion incurred by a ‘cold’ (zero-bias) Class B output stage, while competing on sonic grounds with the best ‘traditional’ Class A and A/B designs [see Investigation, HFN Feb ’15]. Class D amplifiers are one solution – representing the audio signal as a series of very high frequency pulses – and they have improved in leaps and bounds in respect of load tolerance, response flatness, low noise and distortion. Alternatives include Class H, which is the US designation of Europe’s Class G. These employ two or more PSU rails, each of higher voltage, with the lowest voltage always selected to accommodate the prevailing signal. Excess dissipation in the output stage is thus minimised, and efficiency improved.For the headphone amplifier in its HPA4, Benchmark uses THX’s ‘Class H Achromatic Audio Amplifier’ (THX AAA) technology – a further refinement of the breed that uses two or more pairs of DC rails of increasing voltage. Here, however, any rail-switching glitches or crossover distortion in its final Class B output stage are largely eliminated by the use of feedforward error correction. Of course, supreme ‘green’ efficiency is not vital for an AC-powered headphone amp of limited output and the specific THX AAA-888 module used h ere still has a quiescent (idle) consumption of a few watts. In practice, Benchmark is using THX AAA tech on grounds of performance, and so the HPA4 still runs fairly warm! PM



ACE AT ATMOSPHERE


It was one of those real ‘performer in the room’ experiences and I was instantly transported back to the time I spent monitoring the recording as it was being made in the Eindhoven Muziekgebouw back in July. Then the effect, through producer/engineer Jared Sacks’s spare pair of AKG K1000 ‘earspeakers’, was spine-tingling. Listening to the released version [from NativeDSD.com] via the Oppo PM-1s driven in balanced mode by the HPA4, was every bit as emotional, and just as fulfilling as Fedorova attacked the last section of Beethoven’s ‘Moonlight’ sonata with remarkable speed, spirit and precision.That total openness was also much in evidence with Tom Jones’s 2010 album Praise And Blame [Island 274 129-7], with the powerful band resolved with superb impact, but most of all the close-up view of that remarkable voice, notably on the opening ‘What Good Am I?’ but also Sister Rosetta Tharpe’s ‘Strange Things’ or the slamming ‘Burning Hell’. The album may have famously been dismissed pre-release by a label boss as a ‘sick joke’, but listening to Jones giving the songs full commitment through equipment as revealing as this shows just how wide of the mark that assessment was – the sound just drips with atmosphere and sincerity.



RIGHT ON TRACK


The sound here is technically about as immaculate as you’re going to get, but the real beauty of the HPA4 is the way it lets through all the intent of performers, producers and engineers. Play the flat dynamics of a recent release such as Nicki Minaj’s Queen album [Young Money/Cash Money/Republic 00602567712183] and, for all the swagger and attitude supposedly in there somewhere, it sounds dull. But switch to Bill Frisell and Thomas Morgan’s live Small Town set [ECM 2525] and instantly all the presence, ambience and instrumental timbre is restored.So yes, this isn’t a preamp to flatter poor recordings, nor indeed to give so-so source components an easy time, but get it right and it can turn on the magic in a way that eludes many a much more expensive preamp, let alone one doubling as an outstanding headphone amplifier. And it loves voices and real instruments, which allow it to shine, as is clear with Loreena McKennitt’s recent Lost Souls album [Quinian Road QRCD117], which absolutely sparkles, or the even more atmospheric Shine A Light, Billy Bragg and Joe Henry’s ‘Field Recordings From The Great American Railroad’ [Cooking Vinyl COOKCD623], where the ambient effects on these location recordings are often quite literally startling – especially via headphones!Railway platform sounds and voices bubble away in the background, adding to the live ambience, and even the one ‘indoor’ track, ‘Waiting For A Train’ (recorded in the same San Antonio hotel room that Robert Johnson had his first session), has a lovely vintage atmosphere and intimacy to it.The HPA4 can certainly rock out, its prodigious capability when it comes to output levels meaning it can give as much as your power amp or ’phones can take. In fact, it gets louder without the sound changing one iota, so some caution is to be advised if one isn’t to drive partnering components to their limits. But that’s testimony to the purity and skilled design of this thoroughly remarkable product.



ABOVE: No digital inputs here... the HPA4 is pure ‘analogue’ with two balanced ins on XLRs, two single-ended (RCAs) and line outputs also on XLR and RCA (inc mono)



LEFT: Benchmark’s solid little remote covers off input
selection, volume, mute and display brightness


HI-FI NEWS VERDICT

Despite PM’s humorous note of caution, power amp destruction or ear-bashing isn’t what the Benchmark HPA4 is all about. Instead its beauty is that it sets no limits on your system: any failings audible will need to be looked for elsewhere. Yes, it’s a slightly more complex buy than your average headphone amp, its all-analogue design meaning most will need a partnering DAC, but the sound is beyond question.
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 楼主| 发表于 2019-8-8 14:07:49 | 显示全部楼层
Designed to match its compact DACs, Benchmark’s all-analogue headphone amplifier
employs the same THX ‘Achromatic’ tech debuted in its 100W AHB2 power amp  
Review: Andrew Everard Lab: Paul Miller
Benchmark HPA4
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 楼主| 发表于 2019-8-8 14:09:40 | 显示全部楼层
这是一个恰当命名的品牌——其产品通常

提供“基准”技术性能。hpa4不是

继电器开关分步音量衰减器例外

在“可用”105db范围内以0.5db步进校准

顶部+15db至-15db序列,精度为±0.03db

以及-16db至-48db,在±0.09db范围内。在–60db时,错误只是

–0.12分贝。增益也很精确,所以显示屏上的0.0dB实际上是

单位,+6.0db为+5.98db(x2),+15.0db为+14.98db(x5.61)

通过平衡线路输出。失真和噪音正在消失

低音和中音在0.00008%以内

0dbv,增加到0.00018%/20kHz和0.0005%/40kHz[黑色

记录道,图2,如下所示]。频率响应为尺平

(±0.01dB)从1Hz-100kHz,源阻抗是一个敏感的

30欧姆,最大输出为22伏,足以

驱动任何功率放大器,超过卡入,保护

尽管如此,烧焦的烟坑。

通过耳机放大器,最大电压为11.2V(或

209mW/600ohm),最大值为

功率输出为4.4W/25ohm和7.7W/8ohm。

[黑色/红色痕迹,图1]。所以,HPA4不仅可以驱动

头戴式耳机负载最重,但其宽103.3db a-wtd s/n比

无意义的-102dbv(8μv)残余噪声也可确保

非常安静的背景

灵敏的耳机/耳塞。变形基本上不受影响

通过加载,该值与通过测线输出的值一样低。

[图2]但是高频响应有一些非常轻微的调整。

源阻抗较低,小于0.6欧姆,高达10 kHz,增加

至0.78ohm/20kHz和1.5ohm/100kHz,因此响应提示

从0.0db/20kHz到-0.38db/100kHz(空载)非常轻微

至-0.12db/20kHz和-0.7db/100kHz(25ohm)。颗粒物
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 楼主| 发表于 2019-8-8 14:10:02 | 显示全部楼层
Here’s a brand that’s aptly named – its products typically
providing a ‘benchmark’ technical performance. The HPA4 is no
exception with its relay-switched stepwise volume attenuator
calibrated in 0.5dB steps over a ‘useable’ 105dB range with the
top +15dB to –15dB sequence offering a ±0.03dB accuracy
and –16dB to –48dB within ±0.09dB. At –60dB the error is just
–0.12dB. Gain is precise too, so 0.0dB on the display really is
unity, +6.0dB is +5.98dB (x2) and +15.0dB is +14.98dB (x5.61)
via its balanced line outputs. Distortion and noise are vanishing
low, amounting to 0.00008% through bass and midrange at
0dBV, increasing to 0.00018%/20kHz and 0.0005%/40kHz [black
trace, Graph 2, below]. The frequency response is ruler flat
(±0.01dB) from 1Hz-100kHz, the source impedance is a sensible
30ohm and the maximum output a huge 22V – sufficient to
drive any power amplifier beyond clipping and into, protection
notwithstanding, a charred pit of smoke.
Via the headphone amp, the maximum voltage is 11.2V (or
209mW/600ohm) and, with protection kicking in, the maximum
power output is a substantial 4.4W/25ohm and 7.7W/8ohm
[black/red traces, Graph 1]. So, not only will the HPA4 drive the
toughest headphone loads but its wide 103.3dB A-wtd S/N ratio
and insignificant –102dBV (8µV) residual noise also ensures
exceptionally quiet backgrounds when listening with the most
sensitive headphones/earbuds. Distortion is broadly unaffected
by loading, the values as vanishingly low as via the line output
[Graph 2] but there’s some very slight adjustment in HF response.
The source impedance is a low <0.6ohm up to 10kHz, increasing
to 0.78ohm/20kHz and 1.5ohm/100kHz, so the response tips
very slightly from 0.0dB/20kHz and –0.38dB/100kHz (unloaded)
to –0.12dB/20kHz and –0.7dB/100kHz (25ohm). PM
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