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Advice for "cheap" I2S in balanced out DAC (multichannel)
Advice for "cheap" I2S in balanced out DAC (multichannel)
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Old 19th July 2018, 06:09 PM   #1
JMF11 is offline JMF11  France
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Default Advice for "cheap" I2S in balanced out DAC (multichannel)

Hello,


I look for advice for a cheap" I2S in balanced out DAC (multichannel), to match a 4x100W TPA3152 Class D amp and LXminis.


The intention is to replace 2x FX-Audio D802 FDA amps, that finally lack some power.


I have seen on Aliexpress things like this Aiyima Mise A Jour ES9028Q2M ES9028 I2S entree Decodeurs Moulin Bord DAC Carte de Decodage Avec Sortie Symetrique Pour Amplificateur DIY dans Amplificateur de Electronique sur AliExpress.com | Alibaba Group


I'm really not an expert about DACs and would be happy to find a sound solution, which matches the TPA3152 (performance for a contained price).


As it is multi amp, I need 4 channels (which increases the pressure on price aspect).


Help warmly welcomed,


JMF
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Old 20th July 2018, 04:53 AM   #2
abraxalito is offline abraxalito  United Kingdom
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If you don't need more than 16bits then my lingDAC design will fit your bill. You'll have to build all the boards yourself (for 4 channels you'll need 10 PCBs in total) but the BOM cost for each board is under $5.

lingDAC - cost effective RBCD multibit DAC design
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Old 20th July 2018, 05:45 PM   #3
JMF11 is offline JMF11  France
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Hi,


Thanks for the proposal. It looks like a challenge to me, but I always have appreciated your posts related to STA chips, and trust your design.


What looks to me more challenging in the sourcing of the PCBs and of the components. I don't know if it is possible to source (from EU) the different components are reasonable prices in small quantities. Is it a big BOM and do you need to source everything from a lot of sellers ?



Your idea for the PCBs ?


Best regards,


JMF
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Old 21st July 2018, 01:06 AM   #4
abraxalito is offline abraxalito  United Kingdom
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I'm going to be making all the PCBs available as gerbers on that thread, when I've gotten the schematics and BOMs all sorted out.

Good point about the BOM. I looked on Mouser last night to see what the parts would cost if someone were building small quantities and it was pretty expensive compared to what I pay for parts here (like some parts were almost 10X the price) - if you'd like to discuss options by all means send me a PM.
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Old 23rd July 2018, 07:54 PM   #5
JMF11 is offline JMF11  France
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Abraxalito,


I switch back to the forum for general discussion. As you have played with several pieces of my game, maybe you can have a feeling about the difference between:
- the STA326 (as in a FX-Audio D802)
- a LingDAC + TPA325x (3255 or 3251)


Would you have a (maybe quite subjective) pro/cons comparison of those 2 options ?


Best regards,


JMF
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Old 24th July 2018, 01:13 AM   #6
abraxalito is offline abraxalito  United Kingdom
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Hi J-M

Its a very interesting question. I have indeed played with a few FDAs, STA326 being one of them. In the end with these open-loop PWM chips my own experience is that the bass subjectively gets affected by the power supply impedance. This seems to be the case even when I feed the FDA through an output transformer.

Running the STA326 direct from a switching supply was quite a bit less than satisfactory in the bass, it improved a lot when I added a transistor series regulator. In the end though I still felt my TDA8932 beat all FDAs in the bass. This was one reason I've halted development with FDAs - another is there's no low enough power solution at present for portable going this route.

I started playing with TPA3255 in February and realized pretty quick that while the bass was fairly good (but not better than 8932), the HF was way poorer than with FDAs. The problem is the decoupling of the analog signal processing rail - which incidentally is the same problem with the TDA8932. The TPA3255 has an on-chip regulator for this rail (AVDD, around 7.7V) which puts it at a disadvantage compared to the 8932 which doesn't. I have a hunch it might be possible to disable the reg by pulling the output voltage slightly above the nominal 7.7V but this risks blowing up the chip so I've not tried it yet.

So my experience says if you're willing to mod the TPA3255 and improve its AVDD rail, that would be the way to go. If you're not, then keep the 3255 for bass duty only and use an FDA for HF.
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Old 24th July 2018, 07:14 PM   #7
JMF11 is offline JMF11  France
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Again, thanks for the valuable feedback ! So in your experience, we can achieve pretty good performance with open-loop PWM chips. Better than top DAC + "average Class D"


Didi you had at the end a preferred FDA chip (or range) ?


JMF
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Old 24th July 2018, 11:48 PM   #8
abraxalito is offline abraxalito  United Kingdom
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If by 'average class D' you mean a Taobao board (unmodded) for TDA8932 or TPA3116 then most definitely yes. FDAs do so much better in the HF.

I haven't got a preferred FDA - there seemed not to be discernible differences between them. Higher voltage is better though as I normally like to use an OPT, so given that STA326 with its 36V capability would be the best of the single chip bunch. With chips that rely on off-board FETs (D2Audio for example) there's no practical limit.
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Old 25th July 2018, 11:11 AM   #9
JMF11 is offline JMF11  France
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Quote:
Originally Posted by abraxalito View Post
If by 'average class D' you mean a Taobao board (unmodded) for TDA8932 or TPA3116 then most definitely yes. FDAs do so much better in the HF

By "average class D", I had in mind my FX-Audio D802, or the TPA3251 I was looking at TPA3251-4CH-100W | 3e Audio

This last one seems a good design implementation of the TPA3251, with not too many shortcuts.


In parallel, this make me think that it could be worth trying a basic but clean implementation of the STA326, with some clean power scheme and output stage designed for the load (8R). I think that I'm not an as freak as you about bass dynamic and maybe can leave with those delivered by open loop PWM chips.


JMF
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