RP2350 DSP board with AK5534 & AK4458

[bogdansrb]

I've been putting together a DSP board around the RP2350 MCU. I'm planning on using it with DSPi, but it can be a good candidate for playing around with custom code as well.
It has a stereo input via the AK5534 ADC, and 8 channels out using the AK4458 DAC.
The PCB is not finished yet, but I can share a schematic.

 

[markz]

I'm curious why you'd use an MCU instead of a Pico. Admittedly the Pico would add a small amount of cost but it also adds lots of versatility in being able to use newer models or models with more ram or battery + charger.

 

[bogdansrb]

I'm curious why you'd use an MCU instead of a Pico. Admittedly the Pico would add a small amount of cost but it also adds lots of versatility in being able to use newer models or models with more ram or battery + charger.

You're talking about the bare RP2350 vs. a Pico board? That's because a Pico would take up a lot of space on the board.

 

[Ajay]

That looks really nice, a pleasure to read as well! I didn't look at the data sheets for the DAC & ADC, but I assume you're following the application notes closely. Having said that, I seem to remember some measurements of a DAC on ASR recently that used a DAC with a balanced out and an instrumentation-type amplifier to give a single ended output - it was exceptionally good.

I have two/three constructive comments - from a personal point of view! I often end up regretting not chucking in a few headers for unused pins as it seems I always need them in the end... This could also apply to the audio in/out - you might never need it, but it wouldn't harm to allow for balanced-in (if you have space) and possibly balanced-out - although that might be more annoying. The last thing might not be a thing as I don't know what +/- 15V supply you are using, but I dislike unsymmetrical loading of dual-rail power supplies (as do some types of PSU!) so I might be tempted to chuck in a separate lower voltage rail PSU. BTW, I like 5V3 - those that know, know

I look forward to hearing more about it - thanks for sharing!

 

[bogdansrb]

I often end up regretting not chucking in a few headers for unused pins as it seems I always need them in the end... This could also apply to the audio in/out - you might never need it, but it wouldn't harm to allow for balanced-in (if you have space) and possibly balanced-out - although that might be more annoying.

You're right, and I've been there. But what I usually do is get the base functionality done and then expand if needed. Also it's a matter of board size/complexity, at least for the first runs I keep the boards under 100x100mm since they're cheaper and then expand if it's justified.

The last thing might not be a thing as I don't know what +/- 15V supply you are using, but I dislike unsymmetrical loading of dual-rail power supplies (as do some types of PSU!) so I might be tempted to chuck in a separate lower voltage rail PSU.

Indeed it's something that I dislike as well, but having a separate rail means a custom power supply (or two power supplies, which is worse). I haven't been able to figure out a better alternative, but I'm open to suggestions.
I've kept power supplies isolated from each other using pi filters or ferrite beads and the power consumption overall isn't great, so there shouldn't be any issues. Also 15V leaves a lot of headroom.

 

[Ajay]

Indeed it's something that I dislike as well

I can get a bit obsessive with trying to keep things symmetrical, even when there's no gain..... If it was me, I might consider powering it with 5V(3!) and using something like the TPS65131 split-rail DC-DC. But it's more design work, more time and still has a bunch of compromises built in. I'm one of those people that enjoys design work, but if I have too much time I end up going in circles, generating an infinite number of imperfect revisions....

Thanks again for sharing, I hope to get stuck in sometime soon myself, provided I can nail the spec and the design down....

 

[bogdansrb]

Some updates:
- revised the pinout so that it's compatible with the default pinout of DSPi
- added SPDIF input
- added TPS65131 for the split rails
- few other improvements

Waiting for I2S input from DSPi

 

[DatSpeakerTho]

Would probably have more fans if you could just slap a pico onto it.

 

[bogdansrb]

Would probably have more fans if you could just slap a pico onto it.

This will be a ready made board with ADC, so I need all the extra space I can squeeze out of a 100x100 PCB. I have another project with a Pico, DAC and digital inputs only.

 

[DatSpeakerTho]

This will be a ready made board with ADC, so I need all the extra space I can squeeze out of a 100x100 PCB. I have another project with a Pico, DAC and digital inputs only.

Gotcha, any idea on how much it would cost in the end? And how much solder work does one have to do? Exciting times we are in right now with dsp.

 

[bogdansrb]

Gotcha, any idea on how much it would cost in the end? And how much solder work does one have to do? Exciting times we are in right now with dsp.

Haven't done the bill of materials yet so I can't tell what the price would be. But the solder work is extensive, for this reason I'm investing in a reflow oven.

 

[Wesseling Audio Lab]

Single board to accomplish functions of DSPi with peripherals is very appealing to me

 

[TOMSON]

Where do you buy the parts because the NCP163ASN330T1G regulator in the SOT23 5Pin package is not available in Digi Key or Mouser

 

[bogdansrb]

I get them from Mouser. I have a few in stock so it shouldn't be an issue. I think it's a new-ish part so it goes out of stock from time to time.

 

[jmf11]

Hello, I have read about your intention to keep the board size below the 10*10 limit to keep costs low.

Do you go for 2 or 4 layers?

For the assembly of the first prototypes, do you intend to use/order a stencil ? Or to do without?

Jmf

 

[bogdansrb]

Do you go for 2 or 4 layers?

4 layers

For the assembly of the first prototypes, do you intend to use/order a stencil ? Or to do without?

I think I will be going with a stencil for this one since it's fairly complex and there are a lot of small 0402 and 0603 parts

 

[MCH]

Haven't done the bill of materials yet so I can't tell what the price would be. But the solder work is extensive, for this reason I'm investing in a reflow oven.

I can hand solder those packages without issues, but your board will not be easy by hand, not for me at least. The reason being the high density of components around U9, including a few SMD electrolytics very close. I think you are right investing in a reflow oven. My alternative if I was to do it by hand would be to transfer components to the back side.

 

[bogdansrb]

I can hand solder those packages without issues, but your board will not be easy by hand, not for me at least. The reason being the high density of components around U9, including a few SMD electrolytics very close. I think you are right investing in a reflow oven. My alternative if I was to do it by hand would be to transfer components to the back side.

I'm also working on a board that has the Pico and ES9081 DAC, which should be easier to hand assemble (well you probably still need a microscope and hot air station for the DAC and PSU chip). Though this board only has SPDIF input (and USB from the Pico), no analog input.
The big advantage is that the DAC has the analog output (line driver) included, so there's no need for all of those op-amps, resistor and capacitors.

 

[Ajay]

I'm also working on a board that has the Pico and ES9081 DAC

Great looking boards, hope you get to hear them in action soon! BTW, one of the things I find annoying about the Pico is they didn't include USB in the pinout - I know you can bodge it in various ways, but still... It's the same with the Pi - you end up having to use silly bridge cable/adapters on external ports. *sigh*