ProtoDAC TDA1387 X8 project

[hifinet]

https://www.diyaudio.com/community/threa...st-7335700

[hifinet]

My supplier of modules is back in stock. No increase in price.

[Tim Curtis]

My supplier of modules is back in stock. No increase in price.

Fantastic :-)

Maybe it would be worthwhile at some point to develop a Gerber board layout of the module itself in case a long term supply issue arises. This way, assuming the TDA1387 chips themselves can be sourced, the module could made DIY from parts.

[hifinet]

My supplier of modules is back in stock. No increase in price.

Fantastic :-)

Maybe it would be worthwhile at some point to develop a Gerber board layout of the module itself in case a long term supply issue arises. This way, assuming the TDA1387 chips themselves can be sourced, the module could made DIY from parts.

Reverse engineering the module PCB did run through my mind. There seem to be quite a lot of the chips available, but so far the modules are about the same cost as the chips alone, on a per chip basis.

PCB design is challenging for me. The next task is to mount the 40 pin GPIO header in the design tool, so the PCBs can be ordered with the header pre-soldered. That should be fairly simple.

I have a lot of practice hand soldering headers. It takes only a few minutes. I'm a procrastinator, so...

[Skip Pack]

I don't see a huge advantage to soldering the header in. You need that skill level to do the dac assembly anyhow. The more interesting board design implementation might be to set it up to take two dac assemblies with some phase splitter circuitry to create a differential output dac. However!, I probably wouldn't build one if it were avaiable, so this is not a real request. :-)

Skip

[hifinet]

In the YouTube video, Gaby mentions that he will explore the possibility of a balanced output DAC. He seems to have a plan in mind. Hopefully, it works and he will share.

The only requirement is I2S with inverted and noninverted DATA. Inverted DATA would generate noninverted signal output. Usually a 74HC86 data IC, which has four XOR gates, is used.

Some clever engineering would be required to fit two modules, the 74HC86 and the other components in the limited HAT space.

I think a better method would be to have the Raspberry Pi output inverted DATA to another unused GPIO output. I have no idea how to do this.

[Tim Curtis]

I don't see a huge advantage to soldering the header in. You need that skill level to do the dac assembly anyhow. The more interesting board design implementation might be to set it up to take two dac assemblies with some phase splitter circuitry to create a differential output dac. However!, I probably wouldn't build one if it were avaiable, so this is not a real request. :-)

Skip

IMO having the header pre-soldered would be a real convenience and increase the accessibility of the already super fine  ProtoDAC. I couldn't imagine for example ordering a Pi-Zero w/o a header already soldered in.

[hifinet]

I received a question about using ProtoDAC with SPDIF optical input. I did make a ProtoDAC using this SPDIF to I2S DIR9001 board for coaxial SPDIF input up to 24/96. The board I received looked like the one in the link below. The board also has optical input. It works very well with coax, never used it with optical, but it should work as designed. There are three sets of jumpers on the board. One is for the type of I2S. Select 24 bit, I2S. The other is for coax or optical input. And the third was for SCK. I think based on Figure 3 page 10 of the datasheet, you want 512fs, which has lowest jitter. I soldered I2S jumper wires from the DIR9001 board directly to the GPIO 12, 35 and 40 pads (header omitted). The DIR9001 received power from ProtoDAC, which was powered from the 5V/GND pads between the RCA jacks.

Other possible SPDIF to I2S boards use WM8804 or WM8805 (up to 192k coax).

DIR9001

DIR9001 connections to ProtoDAC

[michaelagiles]

Does anyone have any info on the output drive capabilities of the ProtoDac? my Pass BI preamp has an input impedence of 25K and I was wondering if this is sufficient for the obviously "simple" O/P section of the ProtoDac?
Any info appreciated.
I am considering upgrading the pots on the B1 and wanted to get the best match for the DAC.
Thanks!
MG

[hifinet]

Does anyone have any info on the output drive capabilities of the ProtoDac? my Pass BI preamp has an input impedence of 25K and I was wondering if this is sufficient for the obviously "simple" O/P section of the ProtoDac?
Any info appreciated.
I am considering upgrading the pots on the B1 and wanted to get the best match for the DAC.
Thanks!
MG

It shouldn't be a problem. The output impedence should be less than the 420 ohms of the I/V resistor. I have driven my Icepower 500ASP (which has a relatively low input impedence of 8k ohms) using a 10k ohm stepped attenuator without problems.