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

That means, you have 1 input which it’s from tube preamp, then 1 output of tube preamp and 1 output from the Tone board.

1 input = tube preamp
–Vinyl goes in here

1 output = tube preamp
–Vinyl has to go out here which can’t go out to the tone board

1 output = tone board

SPDIF/USB tone board = input

So the only way to use with the Tone DAC is you must connect DAC Output to the preamp Input

Tube DAC is really expensive and doesn’t have high bit rate, Why would you want that? You’re looking for something is not under $300.

Actually, you want to make a short connection between preamp and tone board so you don’t lose the signal or hum.

Have you checked they DIY about the this kind of preamp? I heard there is a hum on certain boards of this design.

I made A quick schema. I inserted it as an attachment.
hope you understand what I meant with it, it was made in just a few minutes using Word. My final schematic will be drawn with a professional program.

the lines coming in above the squares are meant as input(s) and lines coming out underneath the squares are meant as output(s).

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You have another receiver that you want to swap the Khadas between FX and other receiver? I think it would be nice for FX as the main output but require to have amplifier. That’s my intention of having 6SN7 tube preamp as the main output to the amplifier which it’s exactly as your layout.

:yum: I bought two Tone DACs which one goes to the tube preamp and built-in everything includes a router to control the PI/VIM, Another will swap around with other receivers.

Nope only one reveivery, but with multiple rca inputs, I want to use one input on my receiver wired straight to the dac and another input wired to the output of the tube pre amp. So that I can swap between dac or tubed dac on my receiver.

I am very curious on your project, would love to here more of it and see some pictures if you want to!!

Sure will, I got all the parts but haven’t done anything yet. May take couple months.

The preamp is from here. The problem of delay is the manual doesn’t have everything to complete the project. All parts are general which the designer allow DIY to play around. It’s pretty hard without oscilloscope.

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Yes I could imagine that. What about the prescripted parts? As mentioned on the pcb?

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’.

Well, I decided to use with the integrate Amp at the moment, Still missing a lot of parts that on delay to build a preamp. So far so good with the Yaqin MC-100b. I modded the caps for this amp too and upgraded the tubs as well. Sound pretty good. Haven’t tested much with Tone board to see how much it can handle. May be next week, I will test both with linux and windows if it can play SACD ISO


Wow looks cool! Good job intergrading the DAC inside your tubeamp. I also like the fact that you swapped tubes and caps! How is it sounding?

Sound pretty good compare to Mark Levinson amp. Increase the caps value give some extra bass. Still thinking about PI or VM, still have 1 more space on the left for it but With VM, it has enough space to put the Tone on top too but I have to deal with external power. If I can do that, then I don’t need the laptop… lol. How is your PI with Tone? I wonder if it has enough power to drive 2TB usb hard drive.

Nice to hear it sounds good!

Currently, I am running my Raspberry Pi 3 Model B+ with 2 USB drives and the TB DAC connected to it via only a 2.3A 5.0V adapter. I’ve overclocked my Pi to run at max 1600Mhz and min 1400Mhz (only recommended when added external (passive or active) cooling!!) So Powering the Pi while USB drives and the DAC are plugged in should not be any problem :slight_smile:

Cool, I was thinking PI is USB 2.0 so loading a big external usb HD without power may take time.

I dont experience any slow loading files from my USB-drives. Volumio is perfectly build for Pi and works perfect! Highly recommended!!

Shucks! I wished I’d learned this earlier. I was planning on feeding the TB using I2S from the VIM or RaspPi. Why have the I2S lines brought out to the TB 40-pin connector, much less the I2S connector? Seems kind of pointless. Other uses for I2S on a DAC board? Now it looks like I’ll have to use USB. :frowning:

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You can also stream Spotify from USB using the Spotify Converter from AudFree. Then you are able to play the songs easily on your devices. The music is kept losslessly.

Hi Thomas, I can’t agree with you anymore. For me, I also would like to stream Spotify music or local music from USB. Sometimes, I do not use the Spotify Premium, I will download Spotify songs to USB locally for streaming with the help of DRmare Spotify to MP3 converter. It’s a more convenient way to get music.

Yep. That is a workable method. I also use the Spotify Converter to stream Spotify music to USB. It converts Spotify to MP3 so it is easy to duplicate Spotify songs to USB and transfer the songs to my Raspberry device.