The HiFimeDIY UD20 is a true Digital PWM amplifier with no A/D conversion, no preamp or any analog signal path anywhere before the output stage. This makes a very direct link between the digital source and and the outputs going to the speakers, creating a very clear audiophile sound.
Technology
The UD20 amplifier uses the Savitech SA9023 USB receiver to connect to a USB host (computer, iPad etc). SA9023 works in adaptive USB mode and accepts all samples rates from 32kHz to 96kHz with 16/24bits. The digital i2S signal obtained is sent to the St Microelectronics’ STA335BW chip where PCM is converted to Pulse with modulation (PWM) signal and then amplified using DDX® power output stage, enabling it to drive speakers directly. This high quality conversion from PCM audio to DDXs patented tri-state PWM switching waveform provides over 100 dB SNR and dynamic range.
This is quite different from how a regular class D or T amplifier with digital inputs works – which include a DAC which first convert the digital signal to analog which is then passed on to the amplifier section where it is converted back to PWM. The fully digital technology avoid these extra steps of D/A and A/D conversion.
Power
The UD20 can output up to 2x20W at 8ohm and 10W at 4 ohm. It requires external DC power and is very flexible as it accepts any voltage between 5V and 24V. 12V is required to output 2x20W, and 24V 18V is recommended to achieve lower distortion. It draws 120mA (@18V) running without load, and 23mA when in standby mode. It is very power efficient, up to 90% at full output (2x20W). You can buy it together with this power supply.
Functions
The amp is very minimalistic in is functions. There is a volume knob which will also power down the amp to standby when the volume control is set to minimum.
Banana types speaker plugs is used to reduce risk of shorts between positive and negative outputs. The negative outputs are not common and can not be connected together.
The UD20 uses USB Audio Class 1 native drivers for Windows, Mac and Linux, no extra drivers need to be installed. It will work with the same devices as our Sabre DAC support (SA9023 version) – which includes some iPads and some Android devices. More Android devices might work when using the USB Audio record pro software.
Specifications

- Fully digital amplification
– DDX® power output stage
– Up to 2 x 20W at 8 ohm, 2x10W at 4 ohm

- 100dB SNR and dynamic range
– Accept sample rates 32kHz, 44.1kHz, 48kHz, 88.2kHz, 96kHz and 16 and 24 bits
– USB input (no analog inputs!!)
– No drivers for Windows, Mac and Linux. Some iPad’s and Android devices also works.

- Low power consumption 23mA when standby and 120mA when active (@18V)

- High efficiency, up to 90% at 2x20W
– Accepts DC power from 5 to 24V

- Dimensions: 12.5cm x 9cm x 3.8cm including volume knob
| Weight | 0.25000000 kg |
|---|
2 reviews for HiFimeDIY UD20 USB True Digital Power Amplifier
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Andrzej –
Great little amplifier with clear and revealing sound; so as the result music produced well sounds spectacular and the bad recordings not so much. I still prefer this over the muddy sound of my current NAD. I was particularly blown away by the reproduction of voice and acoustic instruments. Bass may not be very deep but ‘tight’ with nice ‘attack’. With my speakers rated at 8Ohm and 90 dB it can easily fill 4×4 meter room at reasonable listening levels. All in all – very recommended. Hope this will help those trying to make decision. Thanks
Ornit –
Hi!
UD20 is a very friendly amplifier, with exquisite sound.
Rock solid clear bass and sparkling treble, but the refinement is very dependent on the quality of power supply. I tried various types of power supply, the dynamic and focus is much better, when supply noise is very low.
THANX!