Help with TPA3225’s and Active x-over (ADAU1701) design

wmcg

Member
2018-11-30 2:06 pm
Hey Folks,

I have been lurking on this forum for a while and based on what i've learned here I've already had a great experience with the TI 3255 EVM board.

Now after picking up a pair of linn kaber aktiv speakers on the cheap, I have set my sights on a more adventurous build and am reaching beyond my limited knowledge.

I have attached a diagram of the design I have in mind which consists of:

2x Linn kaber Aktiv speakers
3x 48V/7.3A Power Supply - (Meanwell LRS-450-48)

2x 3255 Based Amp - (3e audio - EAUMT-0260-2-A)
1x 3255 Based Amp - (TI - TPA3255-EVM)

2x ADAU1701 Based DSPs (3e audio - EDSP-1701-24-A)

So a power supply per Amp. One DSP board for Left and one for Right. I plan to create a crossover in sigma studio for the DSPs based on the specs for the speakers

I would be grateful for any input on this design. My main concerns are:
  1. Does this fundamentally make sense or am i missing something obvious.
  2. Could Splitting the L and R RCA in to different DSP's cause an issue (noise/interference?) since the DSP's are powered from different power supplies.
  3. Are there any gotchas here?

Assuming it would all work and is not going to blow up then there are some smaller niggles that TBH I can just play around with to investigate:
  1. Can there be an issue powering the DSP boards from 2 of the AMPs but not 3rd?
  2. Should I try to copy the crossover frequencies directly from the speaker specs? Or is it likely to get a better result from messing around with the greater range of options the DSP provides?
  3. Would it be a bad idea to hook up all three power supplies on the same mains cable?

Many thanks in advance!

Will.
 

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ernperkins

Member
2009-11-24 8:39 pm
First, thanks for alerting me to 3E Audio. It appears they have several nice products for very reasonable prices. They hadn't been on my radar before.

Second, I think you should post in the Digital Line Level forum since your design does include the ADAU1701 DSP. You're likely to get a lot more responses in that forum.

Third, one concern is using two independent ADAU1701 boards. I'm not sure if using two boards with unsynchronized clocks will cause any problems. In addition, you'll have to re-program each board separately whenever you make a change. The ADAU1701 does support up to 8 channels via I2S outputs and it appears the I2S channels you would need are available on the J5 connector. Adding one cheap I2S DAC board (many available on Ebay) would provide the 5th and 6th channels you need using one DSP board.

Fourth, the short answer to your crossover question is no. We can discuss the different crossover strategies later, but IMO it is very hard to create a good sounding crossover without accurate speaker measurements taken in the cabinet.

And finally, a question: The EAUMT-0050-2-A amp looks interesting, but the "Buy Now" button on 3E's website doesn't seem to work. Is this still available and if so, at what price?
 
Re 2 x adau1701, if the address pins are accessable on these boards you can set them to 2 seperate addresses (not good on the sure dsp) and link one to the other on the i2c bus, then you can talk to both at the same time via sigmastudio. You will have to set two signal paths within sigmastudio so ic1 and ic2, you don't need the boards to be able to have a play with sigmastudio.
 

wmcg

Member
2018-11-30 2:06 pm
Hey Guys,

Thanks for the replies. In the end i build this and it has been working pretty well.

@ernperkins these are all good points you raise. I hadnt considered the clock syncronisation issue. I was prepared to accept all the other compromises in the short term just to get this up and running with a vague plan to looking into passing the audio with the I2S bus in future.

Now ive just managed to get a bargan on an active sub so im going to have to tackle this issue and ill seek help in the Digital Line Level forum if(when!) needed.

About the crossover frequencies, Linn provides the frequencies that they use when using an external crossover (for converting these speakers to 'aktiv' in Linn lingo) so ive gone with those. Hopefully i can configure the DSP (ill try using the pots to adjust the frequency) to allow me to test difference crossover values without reprogramming, once the sub is introduced.

Regards 3e, i spent a bit of time in this forum reading other peoples opinions and they seemed favourable about the kit. I certainly been happy in the limited tested i did, perhaps ill get round to doing and A/B test of TI EVM board against the 3e one but lack of decent single way speakers might make that tricky. The site doesnt always seem to have links to the products, i find it best just to go straight to the page in ebay and see whats there - https://www.ebay.com/sch/3e-audio/m.html They also respond to emails pretty quickly in my experience.

Thanks for the help!

Cheers
 

Mantas35

Member
2021-07-23 3:46 pm
Hi guys, seeking for advice. Planning on biulding two ripole subs, for my open baffle speakers. Questions are: how low can the dsp be set in Hz, can i make a filter just for two subs, with one DSP board? I would take an analog signal from my riia preamp, feed through dsp, and then through a separate subs amp, to power the subs. Anybody tried something similar?