ProtoDAC TDA1387 X8 project

[hifinet]

Thanks for the info @thomaschan . Are you using the 90R grid resistor? The 5670 is an interesting choice. An Uncle Eric's dumpster tube from VTV (Issue 9 page 10).

[thomaschan]

Thanks for the info @thomaschan . Are you using the 90R grid resistor? The 5670 is an interesting choice. An Uncle Eric's dumpster tube from VTV (Issue 9 page 10).

Yes, I use 90 ohm grid resistor. I am planning on building another one with 6DJ8 (based on Audio Note DAC 4) to do a comparison. Would be very interesting. Eventually, I want to build a separate tube DAC which I can use for CD transport.

[hifinet]

I think it would be best to decrease that I/V resistor as much as possible, as long as there is enough gain from the circuit. Distortion of the DAC will reduce with a lower I/V resistance, and it's always best not to amplify distortion. Also speculating that a metal foil (TX2575) resistor would be of value there.

Regarding a tube DAC for a CD transport, the inexpensive DIR9001 boards (SPDIF to I2S) work very well, in my experience.

[thomaschan]

I think it would be best to decrease that I/V resistor as much as possible, as long as there is enough gain from the circuit. Distortion of the DAC will reduce with a lower I/V resistance, and it's always best not to amplify distortion. Also speculating that a metal foil (TX2575) resistor would be of value there.

Regarding a tube DAC for a CD transport, the inexpensive DIR9001 boards (SPDIF to I2S) work very well, in my experience.

Yes, I do find the gain is a bit too much with 90 ohm resistor. I will be tuning this resistor value.

As for receiver chip, I am planning on CS8412. Both Audio Note and Lampizator use this particular one. I do plan on trying CD4398 and AD1865 besides 1387.

[hifinet]

From posts on diyA, the DIR9001 sounds better. Both boards are inexpensive. I have never tried the CS8412 board.

Regarding the CD4398, I have no personal experience. Looking at the datasheet, I don't think oversampling can be disabled, so no interest in that one.

I have an AD1865 DAC (NOSPi with standard version IC), but I much prefer the sound of the Philips DEM multibit DACs to any R2R DAC I have heard, including a discrete R2R DAC (Version 1.3) with hand selected, tight tolerance resistors. I have not heard any of the highest rated (expensive) BB R2R DAC chips.

[thomaschan]

Finally got a chance to put everything together. I have tried to solder 680 ohm resistor and 470 ohm resistor in parallel to the 90 ohm cathode resistor. 680 showed improvement while 470 gave me best sonic results.

[thomaschan]

Finally got a chance to put everything together. I have tried to solder 680 ohm resistor and 470 ohm resistor in parallel to the 90 ohm cathode resistor. 680 showed improvement while 470 gave me best sonic results.

Typo. I actually mean input grid resistor not cathode resistor.

[hifinet]

Finally got a chance to put everything together. I have tried to solder 680 ohm resistor and 470 ohm resistor in parallel to the 90 ohm cathode resistor. 680 showed improvement while 470 gave me best sonic results.

Typo. I actually mean input grid resistor not cathode resistor.

So that is about 75 Ohms. Have you tried any lower values? How is the gain with 75 Ohms?

[thomaschan]

Finally got a chance to put everything together. I have tried to solder 680 ohm resistor and 470 ohm resistor in parallel to the 90 ohm cathode resistor. 680 showed improvement while 470 gave me best sonic results.

Typo. I actually mean input grid resistor not cathode resistor.

So that is about 75 Ohms. Have you tried any lower values? How is the gain with 75 Ohms?

I haven't tried any lower value yet. At 75 ohm, my volume control is at 8:30 to my DIY Goldmund 27 preamp. This preamp is about 12X gain. I plan to connect the streamer to my 6SN7+ 300B tube amp and hear how it sounds first before making any more changes to the resistor.

[GFgen]

Here are cases that I use when there are several HAT'S on top of the Pi.

Older "dog bone" case. Not sure if this is still available.


Newer case meant for stacked Pi's. Still available AFAIK.

Hi do you have a link where to buy the case for stacked pi?