The Pi2Design 503HTA Hybrid Tube DAC thread

Pi2Design 503HTA Hybrid Tube DAC

It’s an hybrid Tube DAC\Headphone AMP\ Preamplifier.



  • Write Volumio to your SD Card
  • Attach the 503HTA Hybrid Tube DAC to your PI
  • Boot it up
  • Install and enable the 503HTA Plugin (from accessories category)
  • From playback options, enable I2S DAC and select 503HTA Hybrid Tube DAC-
  • You will be asked to reboot, just do it
  • This DAC does not have ANY hardware Volume control that Volumio can directly control. To ensure the best audio quality, we suggest to use the handy phisical Volume potentiometer. If you want to control Volume directly from Volumio, just enable software mixer from playback options.

If used with Raspberry PI3, Wi-fi MUST be disabled (or use an external wi-fi dongle). Unfortunately the gate of the FETs ends up just above the wireless antenna, resulting in an audible noise when Wi-Fi is in use.

This thread will be the reference for technical discussions and help regarding this DAC.

Wow is available in the Volumio shop? How it sounds?

Yes, here it is: … -tube-amp/

And here are my impressions:

thanks Michelangelo! Unfortunately is out of my budget… but seems very cool…

I followed the (rather simple) instructions but was unable to make Volumio work with two different 503HTA boards. The main board is a Raspberry Pi 3. Everything seems to work including the GUI via browser and the ssh access and the tube lights up but there is no sound.

How do I debug this?

Dear Bowzee,
let’s try the easy things first, then we’ll see.
First: did you reboot after enabling the driver?
Second: turn the volume knob higher, that might be the thing
third: if you’re using software mixer, please try to reboot or change to none

Hi michelangelo,

  • reboot after enabling the driver? -> yes
  • turn the volume knob higher? -> yes
  • using software mixer? -> no

Also I reinstalled the SD card from scratch (and followed the instructions), got the same results

Sorry If I still start from obvious stuff, but I can’t understand why it should not work.

  • Which PSU are you using? The one from PI2 design?
  • Are you sure you did connect audio out to the right jack? Remember that one is for input and one for output…

Hope that Michael from PI2Design will jump in and help us

Hi michelangelo,

The only thing that someone could call nonstandard, relatively speaking, is the Raspberry Pi 3 PSU, it says 2.5A on the label but the lightning icon shows up with Raspbian, which seems to be a rainbow square meaning the same with Volumio. If this is the problem I will have to go out and buy some more powerful PSU, like 5A or something.

When you see this rainbow square, it means that the raspberry pi is not receiving enough power.

Also, I understand where the problem is: with the 503HTA amp, you need to use a different power supply, it will not work by powering the pi with your ordinary power supply. This confirms my suspicions :wink:

We’ve written this in the product page

So, if you did not buy this PSU (curiosity: did you get your 503HTA from Volumio Shop?) you should use a laptop PSU at 24V and at least 2A. I think that universal laptop power supplies could be your best bet in this case. Let me know how it goes.

I just received my tube amp and started to play with it.

Raspberry PI 2 in use.
Installed Volumio into SD card.
Opened volumio.local and took plugins for tube-amp(“503HTA Plugin”) and power(“cant remember the name”) into use. And restart.

Question is that does plugin power(“cant remember the name”) contain the the RPi.GPIO?

Any way - I did the step:
“Install python’s RPi.GPIO on volumio: (Pi2 only” … _setup.pdf

I also moved MP3’s into MicroSD internal folder using SFTP.
And changed passwords for root and volumio accounts with SSH.

Now everything is working - mostly.
(Am I still missing something?)

There seems to be noise coming from PI2. Usually when
I am mostly using Wifi but I tried to use cable also but noise seems to be there.

Feeling is that noice comes somehow to PI working and when data is read from microSD etc.
I guess this is now the rail issue. … ts/1691242
This is somewhat annoying.

There is talk about soldering in comments … i/comments
Any ideas if that could be solutions?

Or if there would be more some cheaper option somewhere? … rt-apa32us

My first comment seems to be quite big. :wink:

See in the first post:
If used with Raspberry PI3, Wi-fi MUST be disabled (or use an external wi-fi dongle). Unfortunately the gate of the FETs ends up just above the wireless antenna, resulting in an audible noise when Wi-Fi is in use.

You can disable wi-fi from network options -> enable wi-fi to off

Got mine all setup and working great. Love it.

Question - what is the best way to turn it off when not using it?

I was thinking about getting or building a 2 outlet power strip with a switch.

When I use the Volumio shutdown or power off option from the web GUI, it seems to suspend the Raspberry Pi 3, red light still on. The problem is there is no way to turn it back on without unplugging and plugging back in the power.

Also, that power off option does not seem to control the 503HTA Hybrid Tube DAC.

Thanks for any thoughts.



Nice Tube preamp.

is it also possible to combine it with one of the available poweramps?

Thanks, regards.

Hi, I am wondering…is the valve stage just for the headphone out, or is it involved in the line out as well?

In fact is there a line out to go into a pre-amp?


Hi, I have just received my Tube DAC and set it up. Unfortunately it does not work. Checked all tips from the previous posts. Turned off WiFi. Installed relevant PlugIn. Mixer typ is “none”. I do have a power supply of 24V and 5A. I still do not get sound although the GUI shows progress on the titel, but it also says “Failed to open audio output”. Previously I had a hifiberry DAC and it worked perfectly. I have a RPi 3 with the latest volumio freshly installed. Can you help me?

Hi, finally got it to work. Don’t know how! Now I hear a periodic (about every second for a second) high frequency tone when it is switch on. Is that normal? Stopped using it. Is there any idea how to get rid of the tone?

There is actually a couple of pins on the GPIO and unit to control the power to both the Pi and the Tube amp when you turn the volume control all the way down to the ‘off’ position. This enables a graceful shutdown first on the Pi, then signals the tube amp to cut the power. Works very well HOWEVER it requires a few custom python packages and some code.

See page 7 of this guide: … _setup.pdf

Installing the python packages installed all kinds of other crap and I can see now that my volumio instance is becoming a lot less reliable (Gui and Airplay hang, can still SSH in).

Michaelangelo - any chance of you including the Rpi.GPIO package and this configuration in the 503HTA plugin settings so we don’t have to tinker with apt-get and the like? Happy to be a test puppy!


Yeah, as I also ordered a Tube AMP (really great sound with the right source!!): Is there any chance to include the shutdown mechanism via volume knob in the TubeAMP-Plugin? Everything works fine, but the shutdown doesn’t work for me…