Bluetooth DAC

[Mortenhoe]

Hi. Went here to make a user. Found out I already had one. Yay.

So I wan't to make my own bluetooth DAC's. A pocket one for my headphone amplifier, and one for my home stereo system.

I've been looking at these kind of boards. Cheapo CSR chips, with aptx. Already bought one. The analogue output is okay, but not good at all.
2015 New CSR8645 4.0 Low Power Consumption Bluetooth Stereo Audio Module Supports APTx-in Other Electronic Components from Electronic Components & Supplies on Aliexpress.com | Alibaba Group

So my plan was to go full digital from the CSR chip to the DAC chip.

The chip should have i2s capability. I've added a picture with the board pinout.

There are also this alternative. A card ready for i2s output.
DC 5V C10 Bluetooth I2S Daughter Card DAC Board Assembled | eBay But its bigger and more expensive. Also they made an effort to make it run 5V instead. I don't really need that.

The plan was feeding a DAC like those for raspberry pi.
Either a PCM5102
Free Shipping 1PCS PCM5102 / PCM5102A DAC decoder I2S raspberry red core player PK ES9023-in Integrated Circuits from Electronic Components & Supplies on Aliexpress.com | Alibaba Group

or Sabre ES9023
Audiophonics DAC Sabre ES9023 I2S vers Analogique 24bit/192KHZ -in Other Electronic Components from Electronic Components & Supplies on Aliexpress.com | Alibaba Group

I know basic soldering and step up and step down voltage circuits. But this digital stuff is VERY confusing. I have no clue how to connect the first cheapo CSR board to example the Sabre DAC board....

 

[doctormord]

I2S is not working with the CSR8645, only in USB debug mode. But you can get PCM or SPDIF from it.

The latest WT32i or a CSR8670 are doing I2S out. What's wrong with the analog output, any measurements?

The EBay I2S board might work but if it doesn't support native AAC/APT-X lossless it isn't any better than with the internal DAC. (SBC via I2S is still crap) 😀

 

[Mortenhoe]

I2S is not working with the CSR8645, only in USB debug mode. But you can get PCM or SPDIF from it.

The latest WT32i or a CSR8670 are doing I2S out. What's wrong with the analog output, any measurements?

I will be looking into that then.

Which outputs should I use on the CSR8645 to get spdif? I could solder an RCA cable to it and use the coaxial input on my Onkyo?

 

[Mortenhoe]

Found a cheap CSR8670 board. Which outputs should I use for the Sabre DAC?

Attached pinout.

 

[Mortenhoe]

I've been trying to figure this out myself. I can see in the documentation that the CSR8670 chips supports i2s, but in my understanding, the i2s interface is MCLK, GND, DATA, LRCK and BCK. The board only has PCM/SPI outputs.

 

[doctormord]

PCM/SPI/I2S is shared.

 

[Mortenhoe]

Could not figure out the CSR chip pinout. Or clocks and stuff like that. So I bought the I2S ready card. Wrote to the seller. It IS bluetooth 4.0. Ended up choosing the Sabre DAC, since the pins is an exactly match for the bluetooth card.

 

[Mortenhoe]

Finally got all the boards. This is the test setup. Sound pretty awesome even without ground

But?

Range is horrible!

Why?

 

[doctormord]

Is there a groundplane under the antenna at the baseboard?

 

[Mortenhoe]

It is just white. I do not think it is a groundplane.

Range is less than 2 meters :-(

 

[doctormord]

that's what I'm asking for, maybe the plane is under the antenna as well which would the detune the antenna.1

Have you compared with a different source/sink? (So different transmitter/mobile and different receiver?)

 

[Mortenhoe]

I have not tried a different mobile. My phone has lots of range with other bluetooth audio devices. Just not this one. Was hoping maybe I just had to ground something or solder something to the antenna. I remembered seeing this same board on a DAC on Ali. Its sticking out. Seems like a big design flaw from the guy who made this bluetooth i2s board...... :-(

 

[theAnonymous1]

You can try soldering a ~31mm piece of solid core wire to the very end of the PCB antenna. Add 1 or 2mm extra for where it gets attached. Like the pic below but try to get it as close to the end as possible.

An externally hosted image should be here but it was not working when we last tested it.

 

[Mortenhoe]

31mm seems very accurate. Explain? Copper wire? How thick? I got access to alot of types.

 

[theAnonymous1]

31mm is approximately 1/4 wavelength of 2.4GHz. Copper wire preferred; thickness doesn't matter.

I'm no RF expert, I've just seen this done on other Bluetooth devices. The picture is a Bluetooth module on my DS150E clone (car diagnostic interface). I get solid connection and good range, though I never tested how far away I could go. No point walking too far away from a car your working on. 😉

 

[Mortenhoe]

Nice explanation. Thank you very much. I will be trying that 🙂 Could I use a wifi antenna?

 

[theAnonymous1]

I don't know. I tried it a long time ago on a Bluetooth device by cutting the PCB antenna and adding an external antenna and it didn't work. Those tiny surface mount caps you see are part of the tuning circuit, so the circuit probably needed re-tuned.

I would just try a piece of wire first as it's easy to do and undo.

 

[doctormord]

Because "they" just copy antenna designs.. 😀

If that that doesn't work for you, maybe an external antenna will do, patched for the pcb antenna.

 

[theAnonymous1]

I just noticed that Bluetooth board uses a MediaTek MT6622 which is only 3.0.

 

[Mortenhoe]

Oh no. :-(