Connecting a Raspberry Pi 3 model B+ to the Khadas Tone Board


There is no values on the pcb. Only the part #. He let you options to play with the # to get different sound. It’s not the same like others that you put all the parts and values on board.

I heard people on DIY audio forum said the FX-Audio Tube-01 is very decent? I saw there is a version Tube-03 too but that 's like couple bucks cheaper. Do you have anything to compare between tube-01? May be I will get the little toy to play around. If the sound is good, maybe upgrade the coupling caps to make the sound better.


Unfortunately, I am not that familiar with tube (pre)amps… but I will try my best to give you some information/review of it.

When I first plugged in the preamp it sounded a bit harsh and rather “cold”. But after some hours of playing music, the tubes seemed to be played in. The biggest shock from this little cheap tube preamp was for me the bass, with the standard tubes (6J1) the bass sounded rich and was not lacking details. The mid and top range where a little polished but no big difference was noticeable for my setup.

After I tube-rolled the standard tubes for the JAN-GE5654w tubes the sound was a lot warmer yet not to warm or polished. The tubes also needed some play in hours. When the tubes were played in, between the 30 and 50 hours, they sound amazing! Not lacking details or adding its own sound to the music, just a more warm and richer sound coming out of the preamp.

But unfortunately, there is a (big) disadvantage… the tube preamp will add some serious distortion when played on fully open volume. My advice is to not set the volume above the 30/40% and were good :).

I have tested my tube preamp to see what voltage is set to the heaters of the tubes.
I will add the measurement in the attachments.

Also, I have swapped the potential meter with two resistors, because for me the ideal volume setting around the 30/35% and would never be changed, ever.


Thanks for the info. I will give a try later after I finish building the tube preamp. Most tubes need to break-in which a lot people do at least 50 hours. I don’t listen at high volume so it should be good. 1/3 level is good for me.

Be honest, I don’t know how to use the oscilloscope or remember what I had learned from school with basic course. I guess it’s not hard to look at the waveform.

I thought I read somewhere that people even use DV 24V for better sound but not sure the same model as you have.

I’m currently modding my integrate tube amp with better audio caps and high voltage delay to keep the tubes last longer. Still waiting for shipping of the caps. When I am done, I like to hook up the Tone board see how it sounds.


The test result shown in the graph I send in the attachments. It shows the voltage supplied to the tube heaters. The ideal voltage for the tubes heaters to last the tubes as long as possible is 6.3V ac or dc. The graph shows that the amplifier is able to supply a maximum voltage of 8V dc (I believe it was in dc, anyway dc or ac doesn’t matter :slight_smile:).

Since the ideal voltage to be supplied is below the maximum voltage the preamp will always be able to send out a voltage of 6.3 volt which has been set as output.

The most optimal way to break-in amplifiers or loudspeakers is by turning them on for 8/10 hours a week long. By the end of the week the amplifier and loudspeakers are definitely ‘breaked-in’.