My new tube DAC output

[Algar_emi]

See

I started my new Tube DAC

for details and other photos.

[Gunders]

Hmm.. i think i know those sockets(maybe). I have a couple of them myself. Both the ceramic and the type used for the 6DJ8.
I bought mine at www.demostenes.no, the price was about 4 Euro.
The socket used for the 6X4 is a good ceramic socket but the socket used for the 6DJ8 tube is in fact not ceramic, it's some kind of plastic material. They are not very good
for tubes producing much heat(small output tubes). I used some of those sockets in an EL84 amp and it did actually melt a little bit because of the heat

[Algar_emi]

I found the problem with the high distorsion. It was the tube. Hey guys, I begin to understand your love of tubes. It is so easy to unplug the bad one and try an other ones!

Anyway, all my others 6922 tubes test like this (pretty consistent also, incredible for a transistor guy like me :-):

Distorsion (small signal 0dB, 0.767V in 50Kohms, 1 kHz):
0.3 to 0.5%. I will use the 0.3%

Bandwidth: 200 Khz
Noise: <0.5mv

Tubes rules!

[Algar_emi]

I veryfied indeed that the tube go softly into clipping and can drive a lot (in high impedance at least):

Check also the good linearity indicated by the slight variation in the gain.

Distorsion (indicating clipping coming into effect):

Vin(V) Vout(V) Dist(%) Gain
0.03 0.767 0.3 25.6
0.22 5 0.72 22.7
0.43 10 1.05 23.5
0.87 20 1.9 22.9
1.38 33.8 3.0 24.5 (no visible clipping)
2.00 44.6 3.6 22.3 (begin to see it)
2.78 57.7 5.5 20.7 (clipping, see gain is dropping)

This picture is showing the clipping just beginning at 57.7V

[Algar_emi]

Here the three waveforms, small signal 1V but at 20 Khz. Very nice for a small preamp...

[fdegrove]

Hi,

Congrats on the project. This afternoon I went through your posts in the digital section and I feel you did a great job.

Now, if you could tell as how it sounds compared to whatever you feel it can beat?

Thks,

[Algar_emi]

The svotek 6922 is not that sensitive to shock (microphony). Here a small suspension that I want to implement for the tube PCB. They are small rubber post that I found in a surplus store.

I can see small jump in the noise level when I knock on the table where the PCB rest. Vibration effect dissapear when I put the PCB on the rubber post, Great.

[Algar_emi]

Yes me too I want to hear it. I have just to connect all three PCB and try it. However I don't want to rush it. It is late here in Quebec and everytime I tried to complete a project late at night I did some stupid mistake and burn something. It happened with my ALeph30. So I do it slowly but correctly.

I planned to install everything on a piece of wood, use nice interconnect wires and try it with my Copland 277 used as a transport. I also ordered the XO low jitter clock for my two CD players including the Copland. I still have to installed this too..

Bye.

[stokessd]

What's the quiescent current through the tube stage? From personal experience, I've found that less than about 4 mA through a 6DJ8 tube can crank up the distortion figures and lead to less than ideal sound. If you crank your bias up, your distortion figures may drop even more.

I use a pair of 6DJ8 type tubes in an SRPP configuration with cathode degeneration in my tube DAC. I like it and lots of others seem to enjoy it as well. The SRPP stage also has a low output impedance which can be a big deal depending on your cable lengths and cable choices.

Sheldon

[Gunders]

Have you considered to remove the plastic from the capacitors and oil the PCB and the components with linseed oil?