Anybody tried to "hack" an OEM DSP circuit from an active speaker?

[neRok]

I was just browsing some local stores and saw some RCF Ayra Pro speakers for pretty cheap, and they have "FIR 0-phase DSP" - so presumably a decent "DSP chip" inside them. And that got me wondering, if people are selling these with blown speakers/amps/etc, that maybe the DSP part of it could be salvage and repurposed for some cheap DIY adventures? So I found some pics here, and labelled some things, but I don't know that much about electronics...

1. So it's got apparently got 2x class D amps in it. I imagine most of the amp components are on PCB1, but maybe also PCB2? I can't see how the powered-signal is getting from PCB1 to PCB2 though? I wouldn't think any of the 6x black wires are carrying it, because they are much thinner than the speaker wires.
2. Probably some of the black wires are carrying the audio-signals from the DAC(s) on PCB3 to PCB1? I would think at least 3 wires are doing this (2x positive signal wires, and 1x common ground), but maybe its 2+2 with the last 2 being for "control"?
3. So presumably all the DSP action is happening on PCB3, which I scaled up. The big square chip is presumably the smarts, which I labelled "APU" (audio-processing-unit?). Somewhere there has to be a 1 channel of ADC (signal in), and then 2 channels of DAC (woofer + tweeter out). Maybe that's part of the "APU", but maybe it's got something to do with the 5x8-pin chips? (and possibly there is a 6th 8-pin hidden from view near 8pin5?).
4. Originally I was hoping to see a chip that stood out as unique, like maybe it was like a bios chip on a PC that holds the "firmware". At first "3pin" stood out this way (I thought it might have 6 pins), but maybe it's just a transistor or op-amp? So maybe the firmware is stored directly on the "APU", but possibly it's accessible via the pins that I labelled "I/O pins"?

Anyway, what do you think about this style of hacking+recycling in general, and what do you think about this specific example? There's other candidates out there with DSP too (ie. relatively cheap new/used speakers), like the smaller JBL LSR's.

 

[Rednaxela]

Cool idea.

I’ll link to a post of mine from some time back for your reference.

Imagining a successor to the Affordable Accuracy Monitor

more. As a matter of fact, no reason the whole cabinet couldn't be 3D printed (if filled with something solid.) You can really get creative in terms of eliminating internal standing waves and resonances if you have no constraints on the shape. Would love to see what’s possible with a 3D...

www.audiosciencereview.com

 

[MCH]

I have no idea about what is inside there, but in these cases, I would first try to find the datasheet of the DSP chip, if you think you have found enough information and potentially the software needed to reprogram it, next step would be to look for microcontrollers or ROM memory chips on the board, if you find them, bad news, as trying to reverse what is inside there is another level of work, if instead you have headers that gives you access to the DSP chip and you can figure out what those are, then you might have chances.... and so on...

All that said, there are ADAU DSP boards dirt cheap in AliExpress (like 15-20 EUR) that you can program easily with software that is available for free that really make projects like that repurposing not worth anyones time IMO. @Weeb Labs has a few threads about these here in the forum.

 

[antcollinet]

Are you able to read the part number of the "APU"?

And if you want any significant input from us, you are probably going to have to provide much better pictures, with high quality closeups of all the boards.

Though I also agree with @MCH that trying to reverse engineer these boards as opposed to just getting ones that are fit for purpose in the fist place, is probably an exercise in futility.

The video linked in this thread lists some low cost electronics for power, amp and dsp for active speakers.

DIY Perks video: DIY Surround Sound... USING LASERS!

www.audiosciencereview.com

 

[neRok]

there are ADAU DSP boards dirt cheap in AliExpress (like 15-20 EUR) that you can program easily with software that is available for free

Interesting. There's a lot for me to investigate there, but I will definitely check it out.

After a quick search, I noticed that amirm reviewed such a board. Comparing that board to the one I labelled, it would seem that 8pin2 and 8pin3 are the 2 channels of balanced of output, and that the 6 black wires are the 6 signal wires.

Then I found an Alibaba listing that showed the 5 I/O pins for were "USBi connection". I found an ebay listing with some good info - [USBi JTAG Sigma DSP Programmer](https://www.amazon.com.au/USBi-JTAG-Sigma-DSP-Programmer/dp/B0CF8Z53DR)

• This USBi JTAG Sigma DSP programmer can use to programming SigmaDSP series digital signal processing chips. It can works with the ADI SigmaStudio software. The senior developer can use this programmer develop their own firmware for the DSP board. You can use it programming our TSA1701 DSP board or any other DSP board which use SigmaDSP chip.
  
  Support all SigmaDSP series DSP chips:
  • ADAU17xx series(example: ADAU1701, ADAU1702, ADAU1761, ADAU1781, ADAU1772, ADAU1777 ect..),
  • ADAU14xx series(example:ADAU1401, ADAU1461 ect..)
  • ADAU144x series(example:ADAU1442, ADAU1445, ADAU1446 ect..)
  • ADAU145x series(example:ADAU1450, ADAU1451, ADAU1452 ect..)
  • ADAU146x series
  • AD194x series(example:AD1940, AD1941 ect..)
  • DAU series(example:SSM25xx, ADAU19xx, ADAU13xx, ADAV4xx, AD193x, AD195x ect..)

So I guess this RCF DSP is using the same sort of components, and that "hacking" it is possibly possible.

Are you able to read the part number of the "APU"?

No, that's not my pic or speaker unfortunately.

Cool idea.

It would be interesting to see if some of these factory DSP's are only "half used", because then maybe the stock config can be extracted and some room-based filters added?! No need for a miniDSP or anything then.

---

I also had another idea for "hacking", but it's even more "exotic"...

First I noticed the relatively affordable Arturia AudioFuse X8 OUT - ADAT to 8-Channel Analog Output Expander;

Maximum Output Level	+24 dBU
Frequency Response (D/A) 20 Hz to 20 kHz	±0.04 dB
Dynamic Range	120.5 dB (A-weighted)
THD+N	–105 dB (A-weighted

So that's decent performance. It can do 8x channels of 48kHz 24bit over 1x toslink cable, or 4x channels of 96kHz 24bit over 2x cables (so 8 total channels still). So that got me wondering about PC to ADAT devices (maybe USB, or maybe even PCI-E card). I couldn't find many options. The miniDSP MCHStream Box was the best.

Then I started wondering about the toslink port on my PC motherboard. Sure, that's S/PDIF and hence not "plug-in" compatible — but when you really think about it - it's just a blinking light talking a different language - so why can't it be made to work?! S/PDIF protocol allows up to 2*24/196, which is about the same bitrate as 8*24/48. So I guess it would depend if the mobo's have a chip between the "PC" and the port that is doing the signal decoding in "hardware", or if its being done at the driver level in software? And so if it could be "hacked" to blink however the user wanted, then they should be able to do A-DAT. Unfortunately this is all way above my pay grade.

 

[Rednaxela]

It would be interesting to see if some of these factory DSP's are only "half used", because then maybe the stock config can be extracted and some room-based filters added?! No need for a miniDSP or anything then.

Yes. First you can optimise its anechoic response, like @Weeb Labs did with the Swissonics, and then when there is still processing power left, fix the in-room response on top of it.

When you need no further bass management, you can connect any reasonably transparent component upstream and enjoy.

 

[Weeb Labs]

I recall somebody asking me about these monitors previously. The photos do indicate that they should be a suitable candidate for reverse engineering but there are no visible part numbers. The diagram below is purely speculation on my part, having seen many similar boards.

Regarding ADAT, I'm afraid that you will simply never manage to get ADAT out of a motherboard TOSLINK port. The port is attached to an onboard codec, which handles SPDIF and other protocols transparently. It is not implemented at the driver level.