ProtoDAC TDA1387 X8 project

[hifinet]

I have received requests for the "silver caps", like the ones in the ProtoDAC photos. Those are CRC (Component Research Corporation) and usually milspec and polycarbonate. They can be misidentified in eBay auctions as tantalum. The military used them due to high temperature tolerance. Polycarbonate caps haven't been made by anyone in 20 years. Caps to meet the specs were subsequently made with polyphenylene sulfide (PPS). Also an excellent audio film cap, but really hard to find. 

Just speculation. All of the CRC caps now seen are milspec, due to the fact that the US military buys in massive quantities, is very wasteful, and auctions old stuff off for pennies on the dollar.

Since they are now rare, people are asking crazy amounts for CRC caps. If you find them, first, know what you are buying.

Like the other film caps, the best way to tell the type of capacitor is by dimensions. Here are some pages from the civilian CRC catalog.

[Skip Pack]

Yesterday I found and ordered a pair of ERO 10uf mkc caps on ebay. Couldn't find the lead spacing. I'll probably try those on the next build. In any case, potentially promising alternatives are out there, We just have to test them.

Skip

[hifinet]

I am fairly certain they are 27.5mm lead spacing, as are all the radial MKC in those values. Here is the ERO(Vishay) data sheet.

Just for some pricing perspective, here is a WIMA MKC4 10uF 63V from the DigiKey marketplace supplier TAW Electronics.

[hifinet]

I received this question regarding polarity inversion:

"I have a question regarding polarity inversion. The document says that we have to invert the polarity in Moode. Does this mean I can't use Raspberry Pi software that doesn't allow this inversion?"

You can use software without a polarity inversion option. Simply reversing the +/- speaker leads will reverse polarity. Most components such as preamps and power amps do not reverse polarity, but some do. Check your manuals.

[hifinet]

I receive requests for kits with "premium components". The kit comes with components of very high quality, that have been carefully chosen for optimal sound quality. The user can upgrade components.

There are no options for the TDA1387 X8 modules. 

The Texas Components TX2575 Z-foil I/V resistors are the highest quality obtainable, and comprise by far the largest percentage of the value of the kit. 

The WIMA MKP4 metallized polypropylene output coupling capacitors are of excellent quality, but potentially could be replaced and sound quality improved. There are active discussions in this thread regarding polycarbonate capacitors. The "silver caps" (CRC) are rare. I see maybe one eBay listing a year. There are many other choices, many would be a matter of personal taste. Mundorf, for example, manufactures many quality capacitors that could be substituted. One could perhaps even use $400 Jupiter caps. There are size restrictions due to the HAT format of the PCB. They should be film capacitors. The value can be between 4.7 to 10uF. The voltage should be the lowest available for a film capacitor, which will reduce size. The PCB can accommodate radial (restricted to 37.5mm lead spacing) or axial capacitors.

This is where I previously shopped for parts. There were vendors who sold milsurp stuff. Maybe you have one near you.

Here is an article rating a bunch of capacitors.

The power supply decoupling capacitors C3/C4 have a significant impact on sound quality in terms of soundstage, imaging and dynamics. I think these are a matter of personal taste as well. So far, I prefer the Panasonic FR (EEU-FR1A102L and EEU-FR1A102LB) . I have tried Nichicon UKA, FG, Elna Silmic II, Audio Note Seiryu and others. There are size limitations on the PCB. Voltage rating should be at least 6.3V. Would Black Gates sound better? I don't know. 

The I2S resistors are generic metal film. Could upgrading the quality of these resistors to "premium" improve sound quality. Honestly, I am not sure.

[hifinet]

Another film capacitor to try is the PPS (Polyphenylene Sulfide), which was the replacement film cap for polycarbonate 20 years ago. Some say they have excellent sound quality. The one rated in the Humble Homemade HiFi review, an Evox-Rifa SMR 63VDC, only scored a 6. Hard to get and expensive. No personal experience.

Kemet data sheet

DigiKey

[Skip Pack]

Confirming that the 10uf ERO MKC caps are 27.5mm lead spacing. They are very small compared to the ERO 6.8uf MKC caps I got. The 6.8s are 100V and the 10uf are 63V. Shorter and thinner. Do you expect to have Gerbers with the smaller spacing soon? I still have three boards so wiring a pair onto one should be fairly easy.

[hifinet]

Here you are, Skip. That was the motivation I needed to get it done.

2D view of PCB with 27.5mm lead spacing option.

Layers view red is top blue is bottom with measured lead spacing

Gerber files for the ProtoDAC PCB with 27.5mm lead spacing for the output radial coupling caps.

[hifinet]

Skip, the data sheet shows shorter and thinner. Check your measurements with the ERO (Vishay) data sheet in post 105.

[Skip Pack]

The caps I have are consistent with the data sheet. 

10uf 63V:  L = 31.5, H = 20.5, W = 11.5

6.8uf 100V:  L = 31.5, H = 23.5, W = 13.5

I'm curious, if you moved the row of holes/pads for the output caps 1-1.5mm inward toward the DAC chip on the side of the GPIO connector, would the assymetry vs the other side lead to capacitance or inductance issues? that offset would make it easier to make sure the 'red box' caps would have the little nibs on the corners sit on the pcb surface with that cap being more stable. Potentially it would make mounting the MKP equivalents difficult. I'm probably over-thinking this.

In any case, thanks for the new Gerbers.

Skip