DIY TDA1541 USB DAC (Part 3) With Op-amps Analog Output

This post is the upgrade from previous DAC built here. This is a desktop USB DAC with PCM2706 USB to I2S in the non-oversampling TDA1541A DAC.

Then the story to find the best analog stages is begin.

I have read Lukas Fikus explanation on his websites about how well the sound of TDA1541 DAC using single FET at the analog stages. This method is so simple and who doesn't resist to built one? He said the sound is like using a vacuum tube but with only simple schematic. He also comparing his FET design to more complicated HDAM Marantz. But when I applied those schematic like on previous post, there is no way the sound could be good.

The BF245A gate input is so low even the normal current output from the IC TDA1541A DAC could easily distorted the sound. The original schematic from Lukas cannot be applied and some modification needed to makes the distortion lower. The draw back is the analog output level even smaller. I cannot evaluate the sound quality so much because of the distortion flaw and unreliable design. What I heard from it is so much 2nd harmonic distortion.

But the journey for single stages analog output doesn't stop here. I continue to test the others design.

I was looking almost all analog stages design. This is from the simple IV stages using resistor or using FET. But something really got me is the design from Nelson Pass with his Zen IV.

Zen IV design is more promising but the problem with it is the J74 JFET availability. Long time ago when I was built F5 amplifier, I have so much trouble finding the J74. You can see my F5 amplifier built here and also beware of many fake JFET out there. The K170 and J74 already long discontinued and the fakes is easy to spot here.

So I trying the other way. With the same concept as Lukas Fikus, the single FET analog but with JFET schematic from Nelson Pass. The basic idea of this simple DAC IV is the resistor convert the current to voltage then amplify by a single JFET. I took the schematic from JFET Bride of Zen from Nelson Pass. This JFET BOZ was intended to become a pre-amplifier pairing with the Zen power amplifier. But in this DAC application, I will using JFET BOZ to increase the gain after the passive IV stages.

I did a initial test combining the current output from TDA1541A DAC with this JFET BOZ using separate PCB with a great result. No sign of distorted sound on any music played. It also has high level analog output. The voltage required for this schematic can be vary from 13 volt up to 30 volt. The Nelson Pass design for this JFET BOZ is so much better and reliable.

This is the modify JFET BOZ schematic for DAC IV analog stages.

With this great result, then I populated the new components replacing the previous BF245A FET. It is still very simple, yet the same concept as previous Lukas Fikus single FET DAC analog stages.

It didn't take so much time for me to convert from previous setup to this new JFET BOZ setup.

It is all done and I listen to this new JFET BOZ DAC for quite long time using a headphones setup or with my home audio system. I think it is straight 2 days I listening to this DAC on every my listening session and always thinks that something not really right on this design.

Yes, the music is there, but it is not right in the presentation. The sound is un-distorted and the level output is high enough. I believe it is more than 2 volt at analog output. But the three dimensional sound not really presenting really well. I also heard un-realistic treble mixed with very high frequency noise.

Then, I put few capacitors as LPF at the input or at the output of the JFET with also no luck to brings the music to the next level. At this point, this is not a good analog DAC design.

With this disappointment, I cannot see any possibility to improve or to modify this analog design. I just think no way such a big company like Marantz, Nakamichi, Sony, and others reputable audio company still and always using op-amps for their analog section. This is without any particular reason or only aim for the simplicity.

So I design a new board again but now using op-amps for this DAC.

Using the op-amp for IV stages and LPF in this TDA1541A DAC makes me smile again. The sound is correct, without losing any detail, three-dimensional sound presentation and the intimacy of the smooth vocal is right there.

I guess this is the end of the TDA1541A USB DAC journey. For such that simple FET, it is far from perfect sound.

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