ProtoDAC TDA1387 X8 project

[hifinet]

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?

The Geekworm is the one that I personally use. Available on Amazon and other sites. The brown color is a removeable paper protective layer to keep the acrylic from being scratched in the package.  It also comes with a bunch of standoffs.

[Tim Curtis]

I've since switched to this simple top/bottom plate config but I use black nylon standoffs and screws instead of the brass parts (looks better to me) ETA: Same part as @hifinet in previous post.
https://www.amazon.com/dp/B074T7D1V5?psc...ct_details

The other stacking plate product
https://www.amazon.com/gp/product/B07K72...UTF8&psc=1

Nylon standoffs (make-female and female-female in lots of different sizes)
https://www.amazon.com/gp/product/B0B5M1...=UTF8&th=1
https://www.amazon.com/gp/product/B0B5LT...=UTF8&th=1
https://www.amazon.com/gp/product/B0788F...UTF8&psc=1

[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?

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.

With the passive I/V resistor circuit of ProtoDAC, I have noted that there is an inverse relationship between the I/V resistor value and the power supply decoupling capacitor value (C3 + C4). Too low a capacitance and dynamics are lost. Too high and the soundstage depth shrinks. Does this also apply to the Lampizator circuit? The decoupling capacitor might need to be fairly large with the 75 ohms I/V resistance, at least 4000uF (just a guess).

Also, your preamp has 21.5dB of gain, I wonder how it sounds going directly to the preamp with the 75 or 90 Ohm I/V resistor (i.e., eliminate the Lampizator circuit). Or use the Lampizator circuit with a high quality pot or switched attenuator and eliminate the preamp.

[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.

With the passive I/V resistor circuit of ProtoDAC, I have noted that there is an inverse relationship between the I/V resistor value and the power supply decoupling capacitor value (C3 + C4). Too low a capacitance and dynamics are lost. Too high and the soundstage depth shrinks. Does this also apply to the Lampizator circuit? The decoupling capacitor might need to be fairly large with the 75 ohms I/V resistance, at least 4000uF (just a guess).

Also, your preamp has 21.5dB of gain, I wonder how it sounds going directly to the preamp with the 75 or 90 Ohm I/V resistor (i.e., eliminate the Lampizator circuit). Or use the Lampizator circuit with a high quality pot or switched attenuator and eliminate the preamp.

Before I add the Lampizator tube output, I had been using the ProtoDAC with 90 ohm resistor. Sound quality was OK. However the SRPP tube output makes a huge improvement. Especially when I use separate power supply for the DAC and the Pi.

As for the Pi +5V decoupling capacitor, I am using 220uF Nichicon MUSE. I haven't got a chance to try different value yet but I will. At the moment, I am planning on a better power supply for the B+. Looks like a lot of tuning is needed for this streamer.

Will you be building one as well? Love to hear from others.

[hifinet]

Before I add the Lampizator tube output, I had been using the ProtoDAC with 90 ohm resistor. Sound quality was OK. However the SRPP tube output makes a huge improvement. Especially when I use separate power supply for the DAC and the Pi.

As for the Pi +5V decoupling capacitor, I am using 220uF Nichicon MUSE. I haven't got a chance to try different value yet but I will. At the moment, I am planning on a better power supply for the B+. Looks like a lot of tuning is needed for this streamer.

Will you be building one as well? Love to hear from others.

Yes, I would like to try the SRPP with a 6021 medium mu dual triode subminiature tube. This cascode JFET buffer should also be tested.

[DRONE7]

Before I add the Lampizator tube output, I had been using the ProtoDAC with 90 ohm resistor. Sound quality was OK. However the SRPP tube output makes a huge improvement. Especially when I use separate power supply for the DAC and the Pi.

As for the Pi +5V decoupling capacitor, I am using 220uF Nichicon MUSE. I haven't got a chance to try different value yet but I will. At the moment, I am planning on a better power supply for the B+. Looks like a lot of tuning is needed for this streamer.

Will you be building one as well? Love to hear from others.

Yes, I would like to try the SRPP with a 6021 medium mu dual triode subminiature tube. This cascode JFET buffer should also be tested.

That buffer, is that in conjunction with the tube output device or in place of ? Where in the chain ProtoDAC-xxx-xxx would you place it ?

[hifinet]

Before I add the Lampizator tube output, I had been using the ProtoDAC with 90 ohm resistor. Sound quality was OK. However the SRPP tube output makes a huge improvement. Especially when I use separate power supply for the DAC and the Pi.

As for the Pi +5V decoupling capacitor, I am using 220uF Nichicon MUSE. I haven't got a chance to try different value yet but I will. At the moment, I am planning on a better power supply for the B+. Looks like a lot of tuning is needed for this streamer.

Will you be building one as well? Love to hear from others.

Yes, I would like to try the SRPP with a 6021 medium mu dual triode subminiature tube. This cascode JFET buffer should also be tested.

That buffer, is that in conjunction with the tube output device or in place of ? Where in the chain ProtoDAC-xxx-xxx would you place it ?

I am thinking of using the JFET buffer instead of the SRPP. In my experience, buffers always improve sound quality. There is no additional distortion, and adds the ability to drive any load. An SRPP+ circuit (kind of an SRPP plus cathode follower), that can drive lower impedences, might perform better than the SRPP. If you are going to the trouble of using tubes, with high voltage and heater supplies, it makes sense to use a tube buffer.

[DRONE7]

Ah. I have one of those JFet buffers and have just bought the Pass Front End that can be configured as a pre/front end/ or buffer.
Once that's built i will have to try both.
Thanks for your info.

https://www.diyaudio.com/community/threa...st-7323986

[hifinet]

I came across this in my files for changing the Ali cascode JFET buffer to a Pass B1R2. Of course, it is no longer a cascode buffer. What attracted me to this circuit is that John Curl said in a diyA post that you can't improve on the cascode JFET topology in that circuit. How well it has been implemented in this board remains to be seen.

"Changing eBay JFET Cascode Buffer to Pass B1R2 buffer:
you can leave C1 and C3 in , toss C2 out
leave out R1, R2 , R7,R8
leave out Q4 and Q1 , put shorts through C-E holes
and that's it - B1 V2
depending of your JFets Idss , you can put shorts instead of R3 and R5 , or decrease them to 10R ...... or put 20R trimpot between sources , with wiper to out , if you need to trim output offset
I bought some j113/j176 to test my boards before I use my dodofets on them."

[thomaschan]

After surprise results with Lampizator tube output added to the MoOde streamer and 1387 DAC, this time I tried the Audio Note DAC3 tube output designed in 1995. Very clean yet musical. Excellent imaging. Overall it is very different from Lampizator. Initial impression is Lampizator is more musical while AN is cleaner.

https://www.youtube.com/watch?v=FoECICnvbhE