Test report HiFiMan HM801: Power Amp Board V2.0 (report for a newbie)
General characteristics of the amp part of HiFiMan HM801 Power Amp Board V2.0
Output Impedance
18.23 ohm
Characteristics for the high quality mode
About the high quality mode
We make borders for the maximum characteristics for current and voltage by sound signal reproduction quality levels. In general, when the volume level is increased, the sound quality of the amplifier degrade. Approximately as a car above a certain speed becomes less manageable. Highquality mode is a mode in which it is considered that the amplifier works as clear as possible without distortion and corresponds to the equivalent class A ^{F.A.Q.}. As a car at speed with excellent manageability.
Power characteristics of the HiFiMan HM801 Power Amp Board V2.0
Headphone impedance, ohm
Power, mW
Voltage, dBV
32
0.17
22.76
300
1.55
3.32
Recommended impedance for headphones from the range 8  1008 ohm
For InEar Headphones
59  290 ohm
For OverEar Headphones
No recommendation, Amp is too quiet
Characteristics for the maximum mode
Power characteristics of the HiFiMan HM801 Power Amp Board V2.0
Headphone impedance, ohm
Power, mW
Voltage, dBV
32
25.78
0.84
300
6.02
2.57
Recommended impedance for headphones from the range 8  1008 ohm
For InEar Headphones
8  374 ohm
For OverEar Headphones
No recommendation, Amp is too quiet
Analysis and recommendations for HiFiMan HM801 Power Amp Board V2.0 based on the measured characteristics
Analysis and recommendations for HiFiMan HM801 Power Amp Board V2.0 based on the measured characteristics  
Headphones  Areas of using headphones  Voltage Not loaded Max ^{F.A.Q.} / in equal class A ^{F.A.Q.}, dBV  Current in equal class A^{F.A.Q.}, dB(mA)  Noise Isolation Necessity  Total  
3.08 /2.08  7.14  
InEar or Tablet Sensitivity: 126 dB/V SPL Impedance : 16 ohm The type of acoustic design: Closed Examples ±6 dB 
Home or studio, where sound from the headphones does not bother anyone  5 ★★★★★ 
5 ★★★★★ 
1 ★☆☆☆☆ 
3.7 ★★★☆☆ 

Office and home, where people should not hear the sound from the headphones  5 ★★★★★ 
5 ★★★★★ 
5 ★★★★★ 
5.0 ★★★★★ 

Street with active traffic  5 ★★★★★ 
4 ★★★★☆ 
1 ★☆☆☆☆ 
3.0 ★★★☆☆ 

Metro (subway), public transport  5 ★★★★★ 
3 ★★★☆☆ 
5 ★★★★★ 
3.7 ★★★☆☆ 

InEar or Tablet Sensitivity: 120 dB/V SPL Impedance : 32 ohm The type of acoustic design: Open Examples ±6 dB 
Home or studio, where sound from the headphones does not bother anyone  5 ★★★★★ 
4 ★★★★☆ 
5 ★★★★★ 
4.3 ★★★★☆ 

Office and home, where people should not hear the sound from the headphones  5 ★★★★★ 
4 ★★★★☆ 
1 ★☆☆☆☆ 
3.0 ★★★☆☆ 

Street with active traffic  5 ★★★★★ 
3 ★★★☆☆ 
5 ★★★★★ 
3.7 ★★★☆☆ 

Metro (subway), public transport  4 ★★★★☆ 
2 ★★☆☆☆ 
1 ★☆☆☆☆ 
1.7 ★☆☆☆☆ 

Overear Low impedance Sensitivity: 115 dB/V SPL Impedance : 32 ohm The type of acoustic design: Closed Examples ±6 dB 
Home or studio, where sound from the headphones does not bother anyone  5 ★★★★★ 
5 ★★★★★ 
1 ★☆☆☆☆ 
3.7 ★★★☆☆ 

Office and home, where people should not hear the sound from the headphones  5 ★★★★★ 
5 ★★★★★ 
5 ★★★★★ 
5.0 ★★★★★ 

Street with active traffic  5 ★★★★★ 
4 ★★★★☆ 
1 ★☆☆☆☆ 
3.0 ★★★☆☆ 

Metro (subway), public transport  4 ★★★★☆ 
3 ★★★☆☆ 
5 ★★★★★ 
3.7 ★★★☆☆ 

Overear Low impedance Sensitivity: 115 dB/V SPL Impedance : 32 ohm The type of acoustic design: Open Examples ±6 dB 
Home or studio, where sound from the headphones does not bother anyone  5 ★★★★★ 
4 ★★★★☆ 
5 ★★★★★ 
4.3 ★★★★☆ 

Street with active traffic  4 ★★★★☆ 
3 ★★★☆☆ 
5 ★★★★★ 
3.7 ★★★☆☆ 

Metro (subway), public transport  3 ★★★☆☆ 
2 ★★☆☆☆ 
1 ★☆☆☆☆ 
1.7 ★☆☆☆☆ 

Overear Hi impedance Sensitivity: 105 dB/V SPL Impedance : 300 ohm The type of acoustic design: Open Examples ±6 dB 
Home or studio, where sound from the headphones does not bother anyone  4 ★★★★☆ 
5 ★★★★★ 
5 ★★★★★ 
4.3 ★★★★☆ 

Street with active traffic  3 ★★★☆☆ 
4 ★★★★☆ 
5 ★★★★★ 
3.7 ★★★☆☆ 

Overear Low Sensitivity Sensitivity: 95 dB/V SPL Impedance : 60 ohm The type of acoustic design: Open Examples ±6 dB 
Home or studio, where sound from the headphones does not bother anyone  2 ★★☆☆☆ 
1 ★☆☆☆☆ 
5 ★★★★★ 
2.3 ★★☆☆☆ 
Description of the characteristics and recommendations for HiFiMan HM801 Power Amp Board V2.0 on the table of recommendations
In the table, the characteristics are interpreted and then the ratings are given on a fivepoint scale. You can see below the more comprehensive analysis of the characteristics by the algorithms used in the table.
The table provides two main estimates for the amplifier: an estimate by current and an estimate by voltage. The characteristics of the headphones and the environment affect the final desired voltage level from the amplifier output, which must provide a sufficiently level of loudness from the headphones.
Main characteristics of the HiFiMan HM801 Power Amp Board V2.0
The main "universal" characteristics of the amplifier are maximum current, maximum voltage and output impedance.Значения тока и напряжения может быть разделено по порогам качества.
В общем случае, при увеличении громкости, качество звучания усилителя ухудшается. Примерно как автомобиль с определенной скороcти становится менее управляемым. В этом отчете мы рассматриваем два порога.
 Режим эквивалентного класса А ^{F.A.Q.}  высокое качества (как великолепная управляемость автомобиля на небольшой скорости).
 Максимальный режим ^{F.A.Q.}  предельные характеристики, выше которых усилитель или хрипит или невозможно для него выставить уровень громкости выше (когда автомобиль теряет управляемость выше определенной скорости или не может развить скорость выше).
Voltage
 The maximum voltage level ^{F.A.Q.} without load is 3.08 dBV.
 The maximum voltage level in equivalent class A ^{F.A.Q.} without load is 2.08 dBV.
Current
 The maximum current level ^{F.A.Q.} without load is 31.44 dB(mA)
 The current level in equivalent class A ^{F.A.Q.} without load is 7.14 dB(mA).
Impedance
 The output impedance of the amplifier is 18.23 ohm.
Analyse of the output impedance of the HiFiMan HM801 Power Amp Board V2.0
When load is on (headphones were connected) the output voltage level decreases depending on the output impedance of the amplifier. The HiFiMan HM801 Power Amp Board V2.0 has an output impedance of 18.23 ohms.
This is a middleimpedance. With this impedance, the voltage drop at a low impedance load is moderate.
For а lowimpedance load this is optimal gain margin and drop background noise.
If the voltage is 2.99 at the 600 ohm load, then under load of 16 ohm voltage will decreases by 1.55 dB to 1.44 dBV.
Analysis of voltage and current HiFiMan HM801 Power Amp Board V2.0 на графике
One of the main tasks of the detection of compatibility of headphones with a specific amplifier, is to find out whether the amplifier can give the optimum voltage level. That section describes with details how to construct a graph of maximum voltage from the music power from the initial parameters of the amplifier.
Based on the values of the maximum voltage ^{F.A.Q.} levels and impedance of the amplifier, the maximum voltage levels for the headphone impedances of interest are determined. On the graph in the example, these are the impedance: 16, 32, 70, 150, 300 and 600 ohms. Grey columns show maximum voltage levels.
Voltage values are expressed not in volts, but in decibels to 1 volt  dBV. This allows you to compare the volume immediately in dB, which many are used in the equalizer and while adjust the volume.
We are interested not only in how loud the amplifier can work, but also to determine the range on what volume level we can get good quality. So we make estimation according to the voltage and current data of the in equivalent class A ^{F.A.Q.}.
The lilac color area shows the voltage range for the equivalent class A under load without current limitation. This region is constructed in the same way as for the maximum voltage, depending on the magnitude of the load. However, each load value requires a certain current level at the output voltage at the amplifier output. Yellow area indicates the voltage range for the equivalent class A under load with only a current limitation with a margin of 12 dB (correction for a musical signal). From two areas, a green area is obtained  a range that enters both the lilac and yellow zones simultaneously. This is the desired range, which is optimal for the amplifier.
The lower bound for the yellow, lilac and green ranges in the form of the minimum voltage value is determined by the maximum level minus 36 dB. It is often believed that the louder the amplifier is the better, but it is not. If the amplifier is excessively loud, then when you lower the volume level, you often have to deal with different problems: audible background noise or channel imbalance.

Digital volume control  when the volume is lowered by program way or through the controller in the DAC, the useful signal decreases in amplitude, but the background noise remains at the same level. After lowering the volume to a comfortable level, you can hear definitely clear the noise in highsensitivity headphones (or in middle sensitivity headphones if the amplifier is initially very loud / powerful).
In smart phones, tablets and laptops in the low volume area there can be a noticeable contribution of distortions from the software algorithms of SSRC, which are even more destructive than background noise. Moreover, where volume control is performed through the OS (Windows, Linux), the volume control range may not exceed 48 dB and the user will have a choice between the loud sound and its total absence.  Analogue volume control  most analogue controls have an unbalance in the low volume level, when one channel sounds quieter than the other. To obtain a better volume control, use variable resistors from ALPS. In this case, imbalance is observed at much lower volume levels. To obtain maximum quality, discrete regulators (stepped volume control) are used. Но, обычно шаг регулировки в области низких громкости  большой.
Thus, the lower level is limited by the recommended volume control range, and the upper level is calculated based on the current and voltage limits in the highest quality mode for this device, which we define as equivalent to class A.
For headphones, based on their sensitivity, ambient conditions and the required volume level, the required voltage is calculated. If the required voltage value is under the green area, then the headphones will be too sensitive for HiFiMan HM801 Power Amp Board V2.0 and to set the optimum volume level it will be necessary to lower the level by more than 36 dB from the maximum.
If the required voltage value is above the green area, then you have headphones with not enough sensitivitylevel and / or amp with insufficient voltage level in the equivalent class A.
If the value is above the green area, but does not exceed the gray area, then the headphones will give the necessary volume level, but the sound will be less qualitative, because the amplifier will work already in less qualitative equivalent modes AB, B and maximum level.
If the value exceeds the maximum level, then the necessary volume level can not be reach, or will be clearly heard the "wheezing sound" from clipping.
The simplified formula of the desired voltage for headphones is as follows:
V = SPL  Sensitivity + Peak factor  Output voltage + Correction for external circumstances
where:
 SPL  the desired sound pressure in dB SPL at the headphone output.
 Sensitivity  the sensitivity of the headphones to the voltage.
 Correction for a music signal of 20 dB to account for the unevenness of the volume on the sound track.
 Output Voltage  the level of the output voltage of the amplifier in dBV when loaded of the headphone impedance.
 The correction for external circumstances is the noise of the environment and the presence of noise insulation in the headphones.
The analysis for specific headphones can be viewed separately by selecting the appropriate headphone models on professional graphics.
Analysis of use HiFiMan HM801 Power Amp Board V2.0 with headphones of different acoustic design
This rate primarily depends on the acoustic design of the headphones and the field of application of the headphones. Additionally, depending on the acoustic design, a correction is made to calculate the optimum volume level at which headphones are supposed to be used. In closedtype headphones due to noise isolation from outside sounds, the volume level can be slightly reduced, in calculations it is equal to 6 dB.
The table shows the options with closed and open headphones and ratings from 1 or 5.
Recommendation by compatibility of headphones with HiFiMan HM801 Power Amp Board V2.0 based on measured characteristics
HiFiMan HM801 Power Amp Board V2.0 with
lowimpedance highsensitivity headphones (126 dB/V SPL 16 ohm ) не имеет запаса по громкости в качественном режиме эквивалентного класса А в виде 0.78 дБ, но в менее качественных режимах есть запас до 11.48 дБ. Усилитель недостаточен для работы с такими наушниками, он будет тихим в качественном режиме. Есть небольшой запас по регулировке громкости вниз на 23.52 дБ.
HiFiMan HM801 Power Amp Board V2.0 with lowimpedance middlesensitivity headphones (115 dB/V SPL 32 ohm ) не имеет запаса по громкости в качественном режиме эквивалентного класса А в виде 5.76 дБ, но в менее качественных режимах есть запас до 3.16 дБ. Усилитель недостаточен для работы с такими наушниками, он будет тихим в качественном режиме. Есть хороший запас по регулировке громкости вниз на 31.84 дБ.
HiFiMan HM801 Power Amp Board V2.0 with lowimpedance lowsensitivity headphones (95 dB/V SPL 32 ohm ) не имеет запаса по громкости как в качественном режиме эквивалентного класса А в виде 25.76 дБ, так и в менее качественных режимах в виде 16.84 дБ. Усилитель недостаточен для работы с такими наушниками, он будет тихим. Есть запас по регулировке громкости вниз более 36 дБ.
HiFiMan HM801 Power Amp Board V2.0 with middleimpedance lowsensitivity headphones (95 dB/V SPL 60 ohm ) не имеет запаса по громкости как в качественном режиме эквивалентного класса А в виде 20.30 дБ, так и в менее качественных режимах в виде 15.22 дБ. Усилитель недостаточен для работы с такими наушниками, он будет тихим. Есть запас по регулировке громкости вниз более 36 дБ.
HiFiMan HM801 Power Amp Board V2.0 with hiimpedance lowsensitivity headphones (105 dB/V SPL 300 ohm ) не имеет запаса по громкости как в качественном режиме эквивалентного класса А в виде 3.43 дБ, так и в менее качественных режимах в виде 3.43 дБ. Усилитель недостаточен для работы с такими наушниками, он будет тихим. Есть запас по регулировке громкости вниз более 36 дБ.
HiFiMan HM801 Power Amp Board V2.0 with lowimpedance middlesensitivity headphones (115 dB/V SPL 32 ohm ) не имеет запаса по громкости в качественном режиме эквивалентного класса А в виде 5.76 дБ, но в менее качественных режимах есть запас до 3.16 дБ. Усилитель недостаточен для работы с такими наушниками, он будет тихим в качественном режиме. Есть хороший запас по регулировке громкости вниз на 31.84 дБ.
HiFiMan HM801 Power Amp Board V2.0 with lowimpedance lowsensitivity headphones (95 dB/V SPL 32 ohm ) не имеет запаса по громкости как в качественном режиме эквивалентного класса А в виде 25.76 дБ, так и в менее качественных режимах в виде 16.84 дБ. Усилитель недостаточен для работы с такими наушниками, он будет тихим. Есть запас по регулировке громкости вниз более 36 дБ.
HiFiMan HM801 Power Amp Board V2.0 with middleimpedance lowsensitivity headphones (95 dB/V SPL 60 ohm ) не имеет запаса по громкости как в качественном режиме эквивалентного класса А в виде 20.30 дБ, так и в менее качественных режимах в виде 15.22 дБ. Усилитель недостаточен для работы с такими наушниками, он будет тихим. Есть запас по регулировке громкости вниз более 36 дБ.
HiFiMan HM801 Power Amp Board V2.0 with hiimpedance lowsensitivity headphones (105 dB/V SPL 300 ohm ) не имеет запаса по громкости как в качественном режиме эквивалентного класса А в виде 3.43 дБ, так и в менее качественных режимах в виде 3.43 дБ. Усилитель недостаточен для работы с такими наушниками, он будет тихим. Есть запас по регулировке громкости вниз более 36 дБ.