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TOPIC: 4ch DAC-preamp with miniSHARC DRC

4ch DAC-preamp with miniSHARC DRC 5 years 4 months ago #14452

  • nihtila
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Finally my project is at the point where I dare to start a thread here, cause I know it will work :)

This is my first Real project, or a project which I get this far with, so it was very ambitious one. I needed to learn loads of new things but along with getting a working device, that was one of the main goals. So here it is, a DAC-preamplifier built around miniSHARC. The plan is to use it with Genelec active monitors and subwoofer(s). Thus, SHARC is used for digital room correction. I also wanted small form factor since it should sit on my desktop. My requirement was too strict and after some regulator overheating problems and larger heatsink I also needed to change to a bit larger enclosure. Now I could also put the transformer farther away which is one of the weak points of the design. Another one is 2-layer board (and the first factory-made board for me). Being the first Real project, for sure I would make some things differently now, but it seems good!

The scheme approximately is [digital inputs and input selector] -> SHARC -> PCM1792A -> [OPA2134 and LME49724 buffers] -> PGA4311 -> OPA2134. Im using 4 channels and they are all kept balanced from the DAC to the outputs, thus XLR outputs. Then there is Atmel microcontroller (running FreeRTOS - I just wanted to learn it using this project) to control everything, VFD display to show everything, and software with plenty of menu options to set, such as input-wise offset, balances, output offsets, names for inputs, dsp preset (not yet implemented), DAC filter rolloff etc, even IR commands to teach to the device (currently using small Apple remote).

So at the moment it is in a testing phase. Some tuning is maybe needed, at least to the software. Also I try to make it possible to change the DSP presets by using the vol-fp board. I will post here now how the last steps go. I will open a website soonish for my projects, before that I can answer your questions here if you have some.



Startup text



Four balanced output channels, 4 digital inputs, one coax is meant for output in the future, it is not connected at the moment. USB is for SHARC. One dc plug is remote voltage since I had some ideas for it. It doesnt look professional, I have made the enclosure in my toilet so considering that I am happy :D



There are two 2-channel routes.



And SHARC is attached on top of everything.



Basic display shows physical input, input name which can be changed in the menu, dsp preset, filter rolloff and delta-sigma os rate (don't know if this has any significance but I just added it to the menu), and volume. Needless to say software took quite some time, because I also learned FreeRTOS from scratch doing that.



Volume bar is displayed for a moment after turning the volume.



One example of menu item, which is accessed with a long push (short push goes to input selection), push being a button of the rotary encoder. There are more than 10 parameters to change.

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4ch DAC-preamp with miniSHARC DRC 5 years 4 months ago #14453

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Here are the schematics for electronics folks. Its Kicad schematics, the first page is the "overall" root sheet, and following sheets are the contents of the sheet-blocks in the root sheet.

And of course I wont take any responsibility of anything if someone decides to copy some parts. I am just open at least with these first projects since I have no plans to start selling anything (although it would be very nice some day to get some money back for further developments, kinda pocket money from a hobby :P).

If someone wonders about the amount of ferrite beads used, it is partly to use them as bridges in 2-layer board ;)
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4ch DAC-preamp with miniSHARC DRC 5 years 4 months ago #14490

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I also got changing the DSP preset working!

I am using kinda destroyed VOL-FP. I removed rotary encoder and leds to make it smaller, although I put preset LEDs back for debugging. I removed the IR receiver and connected one microcontroller pin directly to where the IR-out was, so IR codes are sent electrically. I am using NEC codes and If someone once tries to make similar, I have one hint for you: you need one repeat code as well! Teaching the commands works without it but not the actual operation. So, some research work with oscilloscope and remote controller was needed, but it works now! B)

At the moment I am not using any feedback but if it seems unreliable (I had some problems with the actual remote when was testing VOL-FP), I will connect the led pins from VOL-FP to the microcontroller. Then I can re-send the code if it doesn't work.
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4ch DAC-preamp with miniSHARC DRC 5 years 4 months ago #14501

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@nihtila

Wow, this project is definitely going as a sticky and we should certainly post some of your pics in the gallery if you don't mind! It's really impressive the amount of details that went into this tiny little box and we want to congratulate you for your work. By all means, if you're interested in building a little DIY card, keep us updated and we could see how we could help.

Thanks again for sharing that neat project and great seeing the creativity of the miniDSP community members!

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4ch DAC-preamp with miniSHARC DRC 5 years 4 months ago #14531

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Thank you!

Yes, of course you can post pics. I could be interested in providing some DIY cards but I'm afraid I don't have time at least at the moment. I want to continue first with further ideas for similar system but based on separate components: SHARC-box with all SPDIF-outputs, separate DAC and preamplifier, forthcoming living room set :)

It would take plenty of time to make this more like a product, although it would be interesting to do so. If I do next version, it will be 4-layer board, probably the transformer would be out of the board (also would be necessary for DIY-board) and with extra space use PCB-connectors and maybe move microcontroller to the main board, to avoid excessive wiring work (and also electrically probably better). I'm still having a bit problems with heating, or maybe not problems but it is generating rather lot of heat. New version would need maybe some switched-mode regulators, or at least two transformers with different voltages. Now the voltage-converting scheme is rather stupid. Also, I didn't plan to use VFD (just found it) but LCD, for sure it looks awesome but it also draws quite a lot of current from +5 VD supply. We will see what is coming, at least this wont be the end of my productive free time since I have the flow now ;)

Here is one more pic, everything attached except the top cover since Im still monitoring some things and checking the heating issue.



And this is the minimalistic yet technically powerful desktop system of mine, there is also small subwoofer under the table. I was just playing with the first room corrections.

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4ch DAC-preamp with miniSHARC DRC 5 years 4 months ago #14535

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Here is a short video of the operation. Forgot to mention in the last post, that making this more of "a product", one big thing would be to make the software upgradable which I haven't done before (without AVR-programmer). As can be seen in the video, the operation is quite smooth but it is still not "final-product grade".

And the VFD is not flickering in reality, as it seems in the video.

Ok, the video doesn't work as embedded, so here is the link.
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4ch DAC-preamp with miniSHARC DRC 5 years 4 months ago #14576

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@ nihtila,

Great stuff.. We just posted your pics in our gallery since your project does really deserve attention! :-)
I like your minimalist Genelec setup.. very neat..

Keep us updated with the progress of your project. A very neat implementation.

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4ch DAC-preamp with miniSHARC DRC 5 years 3 months ago #14688

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Great implementation! :)

I'd like to do a similar project with 4 WM8741 (mono config) and some STeddyRegs, just some questions:

1. Have you used a standard Atmel card or your custom pcb?
2. Could you please provide your FreeRTOS code, or is it top-secret? :)
3. Which kind of aluminum enclosure have you used?

Thank you!
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4ch DAC-preamp with miniSHARC DRC 5 years 3 months ago #14689

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Thanks!

1.
My Atmel card is also custom. It is approximately same size as LCD cards are, meant to fit behind LCD vertically. It is drawn in the same schematics, as can be seen in older post, but its not electrically connected to the main board. So I just drew that part separately and saw the piece out (as Iteads doesn't support real panelizing). Here is one photo of the boards I got scontent-b-ams.xx.fbcdn.net/hphotos-xfp1...2485_205649609_n.jpg

2.
My code is not top-secret, it is just a huge mess :P I was learning things when developing it, and when I got it working I didn't have motivation to clean up the code, distribute it to files in better way etc.. I may provide it at some point, maybe when I get my website running. Although it may be also worth thinking, do I wanna provide all the files for someone to make an exact copy of the device. I do wanna give designs and ideas to DIY community, but some people may have different selfish plans and motivations. Another thing is that providing the software may lead to loads of questions how to modify it. After all, with all the Arduino etc one can create their own software with reasonable effort (or use ICs in hardware mode if software is a no-go). FreeRTOS is by no means necessary, just part of my personal learning :P I can try to help ofc if someone wants to go for that road. And still, maybe I will publish it.

3.
I have used different sizes of Hammond enclosures (www.hammondmfg.com/1455.htm) for my projects. The one used for this is the biggest model. They are sold in almost every electronics supplier. For future projects I am planning to use some quite heavy and professional-looking aluminium enclosures you can find in eBay. I just don't have tools for making holes to thick aluminium, so then I need to order the rear plates from somewhere.
Last Edit: 5 years 3 months ago by nihtila.
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