TP3 voltage

To get 5.25V on TP3, R26 should be cca 1k66.

But as soon as I ground digital board I get 4.9V on TP3.
Of course, I not grounded there is no music. I really must get those V/I transformers ASAP.

Humming problems (solved)

Hi!

I noticed some serious humming sound when I connected DAC to a wall socket (even though not switch was not turned on). Chaning polarity (L with N) did helped, but not completely.

I found out that the output GND of the PSU board has to be grounded.
Since I do not use PSU to supply power to the digital board, grounding was not done via digital board.

Now I still hear some humming (at very unreasonablly high values), but this is result of heaters/B+, I guess.

Well, the break is over - I have to go back to work.

Matej

Minor investigations

Hi!

DAC has been playing for the whole two days now - really nice sound, but know it can be improved a lot.
I've done some measurements:

TP1 = +4.85V (R24 = 1k7)
TP2 = -5.25V (R25 = 2k0)
TP3 = +4.66V (R26 = 1k6)

I really need to "equalize" resitors.

FIL1 = 6.2V
FIL2 = 6.3V

I really need to "equalize" these also. I am thinking of using one PS for both fillaments - this will quarantee same voltage (but will require 2x higher current, which I do not like).

I_dac1 = 22.5mA
I_dac2 = 25.7mA (since TP2 > TP1, I guess)
I_receiver = 18,5mA

Currents are quite small, which is good for my batteries :)

Planned DAC upgrades

Upgrades:

- V/I transformers
- USB in (TOSLINK in?)
- Black Gates on 6922 board (2x 470uF)
- Mundorf's SIlver/Oil decouplung caps (2x 0,470uF)
- other tubes (Amperex 7309?)

Improvements/fixes:
- equalize TP1 == TP2, higher TP3
- equalize filament voltages (redesign filament PS?)
- cap before filament VRs (100nF)
- cap before gretz (cca 10nF)
- PS (C/10 + C + R + C+ C/10)

TODO:
- smart SLA charger
- caps on SLAs

Interesting AN DAC upgrade.

DAC "finished"

I've finally managed to finish my DAC. There where quite a lot of problems to solve, but like I say - it's just a matter of time.




As you can see, I am using batteries for analog voltage section of DAC (currently I have no charger done yet) - cleaner sound.
I had to lower output level of the DAC since it was to high for my amplifier. This is what I do not like - soundstage suffers. But this only means that DAC is capable of quite high output level and can be used without preamplifier :)
Well, now I only have to made a power amplifier and connect it directly to the DAC.

Still, I plan to add USB input to the DAC and do the reclocking (Tentlabs XO-DAC).

Matej