DAC AD1862: Almost THT, I2S input, NOS, R-2R

Thats a shame about only accepting RX0....a waste of it being multi input!
Don't worry Miro I guess there isn't a lot of interest for this and I don't wish to take your time. There are plenty of 'cheap ' spdif switches out there to try i suppose.!
 
EF86 in triode so about 18,5
For tube it is verg silent because of screen, and low distortion
Have now 68k anode R and 1k5 cathode R with 100uf bypass C

I expect it is the iv resistor value I am searching for. When I remove cathode capacitor it lacks some dynamics. I can try another anode resistor value.
Am planning another tube-bjt transistor scheme too.

Step by step i am getting where I want to be. But still OPA627 sounds best, that’s why I am asking around for best values
 
Last edited:
I am not a tube specialist but Mu here seems too much low for a 1 mA output...the I/V resistor value must be high hence distorsion maybe.

You should try to find Loesh Thermionic tube stage article and try tubes with a higher Mu around 35/40. For a resistor no higher than 200.
Try first 200 ohms and draw your shematic here or in the tube section. The C output is way too big imo.
Too much big grid stopper as well ?

An inexpensive E180F nos could be a place to start. 6dj8/ecc88. 6np23 EB....
 
Last edited:
I expect it is the iv resistor value I am searching for. When I remove cathode capacitor it lacks some dynamics. I can try another anode resistor value.
Am planning another tube-bjt transistor scheme too.

AD1862 isn't designed to drive anything other than an opamp's virtual earth. If you're hoping for good results with passive I/V then you may well be disappointed. Current output R2R DACs go decidedly non-linear when their output terminal isn't held very close to GND. I seem to recall there's an ADI paper explaining this, I shall look it out.
 
I have very good result with AD1865 DAC with 180R passive I/V resistor and SRPP tube stage. I used 6N23P tubes in bypassed SRPP configuration. AD1865 has +/-1mA output current too, so this circuit should be good with AD1862.
SRPP gain is about 24-25 so at the end I have 2VRMS output.


For better result you can add 1:5 transformer after the DAC chip and put the I/V resistor to the secondary side of the transformer according to suggestion of Sowter. In this case 620R I/V resistor at the transformer secondary side, and the DAC chip see 25R what is very close to the ideal 0R
 
This is what I used with AD1865. Disregard the first part of the circuit, use only the components what are in the red rectangle. B+ is 225V
I used 1W AN Non Magnetic Tantallum resistors, with V-Cap Odam coupling CAP. Sounds very sweet.

But using a transformer between a DAC chip and the tube stage is a gamechanger. 🙂
 

Attachments

  • AD1865_SRPP.png
    AD1865_SRPP.png
    28.7 KB · Views: 439
  • AD1865_SRPP_PCB.png
    AD1865_SRPP_PCB.png
    57.7 KB · Views: 451
I also like the idea of a transformer. I have a ANK Kits Canada AD1865 Dac kit 4.1 and it has such a transformer. I am making AD1862 now and want to make tube output stage. I like the discussion this is what I needed.
One question, on the AD1862 Dac PCB where exactly is the Line out for left and right channel can somebody guide me? It must be somewhere before OPamps? Thank you