HiFimeDIY UD20 USB Digital Power Amplifier

EDIT: Available now!

We are excited about our new amp, a USB fully digital amp which produces 2 x 20W at 8 and 4 ohm. It accepts a wide range of DC inputs, from 5 to 24V. 20W is reached at around 12V supply. It should be suitable for a lot of different situations, at home with a computer based sound system, portable systems, car systems etc.

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. 
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 – they 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. 
The UD20 can output up to 2x20W at both 4 and 8ohm. 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 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.
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.

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

14 thoughts on “HiFimeDIY UD20 USB Digital Power Amplifier

  1. Georg Hahn says:

    This proposal sounds very interesting. A combination of UD20 and UD50 will provide a high end solution for 2 Way speakers, especially if a GUI could be used.

  2. soundcheck says:


    One more issue.

    Can we expect a device with asynchronous USB interface? Would be nice to have 50W
    and async USB.


  3. patjazz says:

    it would be great to be able to use (program using USB –> I2S ?) the biquads of the STA335BW !
    so we can use it as active cross filter….. (perhaps with 50W version ? )


  4. soundcheck says:

    20W is too low! The amp will quickly raise distortions the closer you get to 20W.

    I’ve been running a TAS5706 based amp for a while. The DDX320 performed much better with the higher power even on 98db/W SPL speakers!!

    Why not 50W?? You could have used a similar powerstage as used in DDX320???

    Good luck.

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