ProtoDAC TDA1387 X8 project

[hifinet]

The phase shift at the corner frequency is 45 degrees. The ideal phase shift at 20 Hz is 0 degrees, but that is not possible. Once you add a first order high pass filter with the capacitor, it will cause a phase shift in the entire audio band (although it is very low and insignificant at 20kHz). The goal is to minimize the magnitude of the phase shift in the audio band.

[eculcea]

It looks the more TDA1387 the better. I think physically I could solder another 8 chips adapter on top of each other to make it 16 chips, from electronics standpoint would this work?
I am a hobbyist learning about audio electronics and maybe this is a dumb question.

[hifinet]

It looks the more TDA1387 the better. I think physically I could solder another 8 chips adapter on top of each other to make it 16 chips, from electronics standpoint would this work?
I am a hobbyist learning about audio electronics and maybe this is a dumb question.

Yes, it works. I removed all of the pins from two modules, and then soldered 7 wires (pins 1, 2, 3, 5, 6, 25, 28) connecting the two boards to the PCB. The IV resistor needs to be reduced in half to about 210R (or less than 215R), since the current will be doubled. This will reduce noise by another 3dB, and also reduce the output impedence. I think the power supply decoupling capacitors will need to be doubled.

I did not hear much of a difference in sound quality, but there were some limitations in that I used standard metal film IV resistors, and I didn't double the decoupling capacitors.

[dwhacks]

So I've been using my Protodac with moode for quite some time, and its excellent! I had enough parts to build another, with some different caps and an rpi Zero 2 W, so I figured I would do that and us raspotify for a garage/outdoor player (I know I know, no lossless from spotify).

My question, is does anyone know how to invert polarity there? I don't want to do it at my speakers because I use different sources sometime, so it would be best to do it on the pi, like done with Moode and CamillaDSP.

I think I should be able to do it with ALSA, but I have no idea where to start, and googling made me even more confused!

[hifinet]

So I've been using my Protodac with moode for quite some time, and its excellent! I had enough parts to build another, with some different caps and an rpi Zero 2 W, so I figured I would do that and us raspotify for a garage/outdoor player (I know I know, no lossless from spotify).

My question, is does anyone know how to invert polarity there? I don't want to do it at my speakers because I use different sources sometime, so it would be best to do it on the pi, like done with Moode and CamillaDSP.

I think I should be able to do it with ALSA, but I have no idea where to start, and googling made me even more confused!

For a garage/outdoor player, I doubt that you can hear the difference with inverted polarity. 

Raspotify says "If you’re looking for a turnkey audio solution for Raspberry Pi’s with Spotify Connect support we recommend moOde™ audio player."

[dwhacks]

That's probably true, but I still would like to have things "right". I could run Moode, but lately the spotify portion of it has been crashing lots. At least the latest release has an auto-restart for the service, but still its not super solid. Raspotify seems to have less issues, and I just assumed a more simplified player would run better on the Zero.

I'll keep diggin.

[Lolkapies]

After changing cheap WIMA and Mundorf MCap capacitors to Jantzen Audio Superior Z-Cap magic happens, the sound has gained an additional dimension, these capacitors are very musical.

Now I would like to use good I/V resistors, will Charcroft Z-Foil 430R be good, have you tried other precision resistors like Vishay Sfernice precise 0.01%. Will there be a big difference compared to Dale metalized resistors?

[hifinet]

After changing cheap WIMA and Mundorf MCap capacitors to Jantzen Audio Superior Z-Cap magic happens, the sound has gained an additional dimension, these capacitors are very musical.

Now I would like to use good I/V resistors, will Charcroft Z-Foil 430R be good, have you tried other precision resistors like Vishay Sfernice precise 0.01%. Will there be a big difference compared to Dale metalized resistors?

Precision resistors are not really needed, and they will be a waste of money. Foil resistors must be trimmed to obtain the correct resistance value. Charcroft Z-foil should be the same as the Texas Components Z-foil. I think Vishay make Z-foils in Israel. 430R is close to the upper limit of resistance. Some modules may clip with a 430R I/V resistor at 5V supply. The kit uses a 420R value. For a standard value resistor, 390R would probably be a better value. Output will be 0.6-0.7 dB lower compared to 430R. The power supply coupling caps may need to be slightly larger in value to compensate.

The common characteristic of the best sounding I/V resistors seems to be noninductance. The Caddock TF020 thick film resistors have been reported by others to be very good in a similar application, but they are huge. Some preferred the Caddocks and others the metal foil. I think that other thin or thick film resistors would certainly be worth investigating.

[eculcea]

That's probably true, but I still would like to have things "right". I could run Moode, but lately the spotify portion of it has been crashing lots. At least the latest release has an auto-restart for the service, but still its not super solid. Raspotify seems to have less issues, and I just assumed a more simplified player would run better on the Zero.

I'll keep diggin.

I am using picoplayer, has very nice features and also you can use a display for the raspberry pi.

[hifinet]

A bit more on the Caddock TF020 as I/V resistors:

Caddock TF series: I think this is a discontinued series. Places like Percy Audio have these. "Excellent alternative to the more costly Vishay S102 [TX2352], and preferred over the S102 by some..." and "This is absolutely the most transparent resistor Caddock manufactures and ideal for ultra critical applications where the best possible sound is required." Listed at $6.95 USD each, so much less expensive than bulk metal foil.

Another possible candidate are the new tantalum nitride thin film SMD resistors by Vishay (PNM), Yageo (NT series) and Stackpole (RTAN series). Currently there is very limited availability of resistances, but they are very inexpensive (<$1USD). Shinkoh of Japan previously made through-hole tantalum resistors. Now Audio Note makes them, but they are fairly expensive (but still less than metal foil).

I think the Z-foils (TX2575) will be hard to beat.