DIY active crossover in development - looking for inputs

[DannerD3H]

Amazing project. Let me know if you need a beta tester!

Haha, thanks for the confidence

 

[DannerD3H]

Basically the market needs something like a minidsp flex but for half or less than half the price of the flex unit.

That won't be this DSP, that's for sure xD

Also think about it.. some people gladly pay 1000s of dollars for a stereo DAC.. that's ONE stereo DAC. A DSP like this has 4 stereo DACs..

I think it will be very difficult to beat the minidsp products on price. Especially for a DIY product. Maybe someday if this succeeds I may try to scale it back and see how cheap it can be done while still sound great for stuff like Bluetooth speakers and so on. But that will be in the next decade xD

 

[DannerD3H]

The opposite, market needs a decent processor even at double the flex money.
And I'm not talking about SINAD.

That's the product I was looking for and didn't find. That's why I started this project. The DSPnexus is probably the closest.

Out of curiosity. I have not tried or heard the flex. Only the older 2*4hd. Can you explain what is wrong with the flex?
Is it bad? Does it lack features? Does it sound bad? Or why does some people seem to be unhappy/not satisfied with it? Just not fancy enough?

I mainly just wanted to use sigma studio and have a few more features than the flex it provides.. and a challenge

 

[Bjorn]

Just a proper cabinet cost about half of a miniDSP Flex to manufacture (unless you manufacture very large numbers). Half the price or less of a Flex isn't possible with the upgrades we need.

The Flex is mainly lacking the following:
- Only 4 channels
- No trigger output
- Limited to 2048 FIR taps per output
- Jack outputs is annoying because cables don't sit well
- The cabinet get's super warm, never a good sign for the life span of the product
- The display shuts down after a while and can't be turned on all the time
- No ability to be controlled from a tablet or phone
- And as a speaker manufacturer you also want to lock away crossover settings and give global correction options to the customer, something miniDSP can't do

Flex Eight has obviously 8 channels but lacks additionally:
- No balanced outputs
- No analogue outputs
- No FIR capability

Sound quality of Flex is great, though I would prefer AKM velvet chips.

 

[MCH]

That's the product I was looking for and didn't find. That's why I started this project. The DSPnexus is probably the closest.

Out of curiosity. I have not tried or heard the flex. Only the older 2*4hd. Can you explain what is wrong with the flex?
Is it bad? Does it lack features? Does it sound bad? Or why does some people seem to be unhappy/not satisfied with it? Just not fancy enough?

I mainly just wanted to use sigma studio and have a few more features than the flex it provides.. and a challenge

The minidsp flex is basicallz a 2*4hd with display and volume knob and updated performance, i think it is great solution for a lot of use cases.

What the flex and most of other minidsp products can do that a diy device will never do is the dirac live plugin. I really don't understand what people complain about: if you are in a budget, you still have the option of the 2*4hd.

 

[Sokel]

That's the product I was looking for and didn't find. That's why I started this project. The DSPnexus is probably the closest.

Out of curiosity. I have not tried or heard the flex. Only the older 2*4hd. Can you explain what is wrong with the flex?
Is it bad? Does it lack features? Does it sound bad? Or why does some people seem to be unhappy/not satisfied with it? Just not fancy enough?

I mainly just wanted to use sigma studio and have a few more features than the flex it provides.. and a challenge

What @Keith_W and @Bjorn said above with the addition of :

M

'DSP Measurements and Rising Noise Floor'

Feb 25, 2023

In several threads related to DSP platforms I've seen requests for measurements with filters engaged. I thought it unlikely that implementing filters in a DSP would have measurable effect on noise / distortion other than the obvious change in the fundamental, however @Sokel recently mentioned that he returned his miniDSP Flex after observing noise / distortion issues with filters applied. This piqued my interest as a long time DSP user and I decided to explore it for myself.

The first issue is what filters to use and what tests to run. I decided to use filters for my LXmini + sub...

• mdsimon2
• Replies: 200
• Forum: General Audio Discussions

• 

I'm afraid I've been out long enough to play with all shorts of DSP or analog el. x-overs that I stayed with what my speakers had in the first place
(not that I don't still play with lots)

I may be one of the outliers here and I'm gonna sound like the paranoid about safety I am, but such gear is usually the last link before the power amps.
In addition they have to control a gazillion of levels and gain, from In to Out.

So, what I would want?
I would want all the goodies a strong DSP carries in terms of doing the filters, with enough horsepower for FIR at any combination BUT manual, analog gain settings at its end.
Some nice, relay based R2R solution, rock-solid about protections, etc.

Did I say double the price? Make that x3 or x4, I would still be happy.

 

[Davey]

Flex Eight has obviously 8 channels but lacks additionally:
- No balanced outputs
- No analogue outputs
- No FIR capability

Sound quality of Flex is great, though I would prefer AKM velvet chips.

The Flex Eight does have analog outputs and FIR capability.
Maybe time to get yourself up to speed???

 

[Bjorn]

The Flex Eight does have analog outputs and FIR capability.
Maybe time to get yourself up to speed???

I said balanced outputs, which it doesn't have.
You're right about FIR, but only on the inputs, thus it's extremely limited.

 

[Davey]

You're right about FIR, but only on the inputs, thus it's extremely limited.

Not really. The input channels is the preferable FIR location, for both resource allocation and overall system functionality.

 

[Bjorn]

Not really. The input channels is the preferable FIR location, for both resource allocation and overall system functionality.

It means one can't use FIR for crossovers for the eight channels. For me, that's really were FIR shines. There's also only 2096 taps per the two input channels.

 

[DannerD3H]

The minidsp flex is basicallz a 2*4hd with display and volume knob and updated performance, i think it is great solution for a lot of use cases.

Thanks for the comparison. but updated performance? does it sound better or just measure better?

What the flex and most of other minidsp products can do that a diy device will never do is the dirac live plugin

True, but.. I do not think I will ever need this. Im no expert in what these programs can do, but so far I can do better room correction myself than at least audyssey or what eveer Denons version is called.

 

[DannerD3H]

I may be one of the outliers here and I'm gonna sound like the paranoid about safety I am, but such gear is usually the last link before the power amps.

You certainly have a point. I also had a few fuckups along my jurney here. The worst one so far was accidently feeding 0dBFS white noise to a 300W amplifier connected to a set of small bookshelf speakers (analog xo inside).. The tweeters did not survive that xD
So I know how you feel. But then again, this was a very stupid mistake from my side and i learned from it. But it is clearly a risk.

I would want all the goodies a strong DSP carries in terms of doing the filters, with enough horsepower for FIR at any combination BUT manual, analog gain settings at its end.

The analog volume contorl is also my end goal. Not sure if it will ever happen as I know its not super simple to avoid pops and whatever...
But for now, what I did was to make my amplifier input buffer with adjustable gain. I will then adjust it accordingly to whatever driver it will be paired with as to allow full scale signal in DSP and analuge outputs while limiting the output power of the amp. Not the most elegant solution, but it works none the less.
On top of that, as I explained, I will mute all analouge outputs via relays unless all power supplies are good and DSP outputs a valid un-mute signal.


Again, interesting reading in that other thread. I certainly have some learning to do to optimize my filters it seems. For the last couple of months I have been playing with amps and achiveing good noisefloor so have basically just used the DSP as a preamp with volume control. no filters, just passthrough. And there it sounds really great!

 

[Davey]

It means one can't use FIR for crossovers for the eight channels. For me, that's really were FIR shines. There's also only 2096 taps per the two input channels.

That's exactly what FIR correction on the input does......unwrap the phase response of the system crossover(s). (Two, three, four-way, whatever.)
I'm puzzled by your premise and think maybe you need to reset your understanding of the capabilities and configuration.

Anyways, this is off topic for the OP's thread.

 

[Lipaz]

That won't be this DSP, that's for sure xD

Also think about it.. some people gladly pay 1000s of dollars for a stereo DAC.. that's ONE stereo DAC. A DSP like this has 4 stereo DACs..

I think it will be very difficult to beat the minidsp products on price. Especially for a DIY product. Maybe someday if this succeeds I may try to scale it back and see how cheap it can be done while still sound great for stuff like Bluetooth speakers and so on. But that will be in the next decade xD

First of all: congratulations, very nice project, and you are dedicated. )

As for the market, I’m looking for a very same kit, but won’t have time to build from scratch. Hence I know what is happening on the market. Partially related to covid era, but also for greedy marketing hands.
miniDSP… they managed to beat their own minisharc kit projects, cancelling them with EOL since 2019 systematically, including the balanced 2x8 minisharc kit, that is perfectly capable for this very same project you are doing here. It was available in some stores still for around 360€ maybe even 2 years ago. You could have balanced in outs / RCAs / digital inputs and the minisharc plugin perfect for 4-way active crossover stereo kit for less than 500€ incl. everything. Now you can buy a stripped down version for 800€ capable for much less apart from
Dirac Live… If you want about the same IOs and balanced, there is HTx for 1300 €? I’m not interested in Dirac Live, nor in 8 inpits or hdmi… I just need a clean sounding active xover, which they do not provide anymore.
This is what they shut down, and likely high license fee with Dirac and contracts plus other upfront regulatory fees why they sell it for more than realistic.

Hypex is the cheapest option to have mint 8ch amp dsp today, until Fosi will incl. PFFB in all their stereo amps (not necessary though in my opinion) and will come out with a 2in 8out dsp solution.
For cheaper options, just go for the openDRC-DA8 on second hand market and pair it with 4 Fosi ZA3. You have a superb DSP amp with 8channels of about 60-80w/ch @8Ohm for 700€. I don’t think unbalanced audio matters if cable is decent and about 20cm long till the amp.
Half the sum of a hypex setup, but almost there.

Either I will jump on the FusionPlate train and make them work in a rack for easy cabling (depends how soon I finish my home studio), or if Fosi will advance (or Wiim… very good too) I’ll check they offer as well.

Good lick with your project! Nice!

 

[voodooless]

This is a really nice project, showing how much one can do by simply mixing and matching existing components and incorporating some of one's own ideas. Prototyping this kind of stuff can be really quick Love the enclosure design, even though the cooling fins are totally pointless, they give the whole thing some authority.

Several comments:

In general: copy from the best. And the best are currently many of the Chinese companies that made optimization for cost vs performance an artform. Look at what they use in their products. This goes for muting circuits, digitally controlled analog volume control chips, power supplies, etc... There are plenty of PCB shots out there from many of these products to use as inspiration.

I will mute all analouge outputs via relays unless all power supplies are good and DSP outputs a valid un-mute signal.

You don't really need classical relays for this. They are bulky, expensive, and will eventually break. You can get solid-state relays or even specialized chips to do this. Much cheaper, simpler, and more reliable in the long run.

As to the DSP, your current choice is a logical one. It's easily available and has decent enough performance as far as IIR goes.

If you really want more horsepower, the dedicated hardware solutions quickly get much more expensive, and much more complex, and the relative gain is low.

To make a real leap, a general CPU-based architecture is probably the way to go. One could make a DSP solution using a Raspberry Pi Compute Module 5, add the DACs, an ADC, and digital inputs coupled to ASRC. GPIOs can be used to control the whole thing. Add Wifi or LAN, CamilaDSP, and streaming options, and you have a self-contained, low-latency, easy-to-use platform that can handle all the DSP you might ever need. A board with HDMI (E)ARC) might also be an interesting add-on to have, btw.

 

[DannerD3H]

Good lick with your project! Nice!

Thanks!
And thanks for the inputs from your experience. I am no longer interested in any commercial product though. I truly believe that this project will knock the socks off the fusion amps.. And its much more fun xD

I have been quiet for a while, but that dosen't mean I gave up

I actually just finished the design of my own PSU and my first DAC module! I am very exited to see if it all works
I must admit I was surprised by the complexity of PSU and DAC design compared to the DSP PCB. Its not that I thought it would be super easy, but still being new to electronics I was fairly ignorant to how deep a rabbit hole a "simple" PSU can be.. And I also knew that DAC(analog audio in general) is as much of a science as it is art and snake oil, but man.. it took some time to get a clear picture of what matters, what don't, and accept what my own skills/time can handle. Finally deciding what level I was aiming for for a start.

The PSU is split in three sections

1. First takes 100-240V Mains and makes 5V with a IRM module. This is my standby PSU, its always on. It has a relay to control the mains supply to the next module. The 5V is fed directly to a future uC (Pi most likely) and filtered with a PI filter to supply the DSP core and digital input modules like SPDIF, USB BT and so on.
2. Second module takes mains AC from the relay and creates +/-15V with two IRM modules. It is then filtered with a PI filter for each rail.
3. Last module is the analog supply which uses a bunch of filtering and low noise LDO's to generate +/-13V for opamps, 5V for digital parts of DAC's and ADC's, 6V as a seperate analog reference.

This PSU structure is taken directly from topping DX9 DAC.


The DAC is based on a AKM AK4493SEQ. I chose this chip as it was the AKM chip I felt most comfortable in implementing and I had found some good reference designs with it, namely a DAC designed by Tomi Nihtila (See his design here: https://kaamostech.com/product/w-dac-xlr/). Big thanks to him for publishing his designs, I have learned a great deal from his page and YT channel! Probably wouldnt have ahd a chance of succes without it.. now I at least have a hope it will work

My DAC is a module that gets connected to the DSP and PSU thru a distribution PCB in one end and to a output connector in the other end. For now I use XLR, but will later try to output all left channels thru one ethercon connector and then all right channels thru another ethercon connector. I believe for a 50cm cable this will be just as good as XLR and clean up wiring tremendously with just a single ethernet connector from the DSP to each amp. This will also eliminate risks of wiring the amps wrong.
This is what the DAC module looks like:

The reference supplies are delivered with a separate LT3042 for left and right channel.
The output stage is made from a OPA1656 for filtering, and a OPA1632 for line driving and gain. All caps in audio chain is C0G with the option to replace the critical ones with FILM as on the picture. All resistors are MELF 1% for testing. If everything works, then I will compare the performance with a 0.1% MELF build.
The Mute relay is controlled by a circuit that prevents unmuting if supplies are missing or DAC IC isn't powered up. This section is particularly inspired by Kaamos, W-DAC.

 

[DannerD3H]

This is a really nice projec

Thanks!
And thanks for your great inputs!!!

cooling fins are totally pointless,

Yeah on the DSP they are, it was just done to macth the power amps. However, I also changed the design of those drastically so the final DSP and amps will look more like something similar to the VOLUMIO PRIMO. I will keep the heatsinks internally with holes in top and bottom plate and eliminate fans completely as I got tired of them in my prototypes already even though they are Noctua fans now.. xD

There are plenty of PCB shots out there from many of these products to use as inspiration

Exactly what I do.. MY PSU for example looks very similar to that in Topping DX9 O

solid-state relays or even specialized chips

Hmm interesting, any specific components you can recommend?

To make a real leap, a general CPU-based architecture is probably the way to go

Yeah, a Pi with vanilla DSP is on my radar.. But I know nothing about it at this point and I love SigmaStuido. So until all the analog hardware stuff around the DSP is nailed down, I will stick with the ADAU1466.

A board with HDMI (E)ARC)

I would love to have this.. but its a bitch.. I havent't found anything module like I can by and put in my case that outputs i2S.. do you know of any?
I cannot do any HDMI stuff myself as its all blocked by the HDMI licens, which only companies can get.. So Im locked out of HDMI unless I can find a premade module..
My current solution is still having a AV/suround processor and use preouts (preferably digital even though this is rare/expensive) for movies. And use my SPDIF/USB inputs for music streaming

A HDMI based i2S input is of course doable though

 

[voodooless]

Hmm interesting, any specific components you can recommend?

No, not really. Maybe ADG884 or MAX4910?

I would love to have this.. but its a bitch.. I havent't found anything module like I can by and put in my case that outputs i2S.. do you know of any?
I cannot do any HDMI stuff myself as its all blocked by the HDMI licens, which only companies can get.. So Im locked out of HDMI unless I can find a premade module..
My current solution is still having a AV/suround processor and use preouts (preferably digital even though this is rare/expensive) for movies. And use my SPDIF/USB inputs for music streaming

The easy way is to just buy an existing cheap HDMI audio extractor with ARC support, rip out the PCB, and find the I2S pins. Making your own PCB for this is probably a no-go.

A HDMI based i2S input is of course doable though

Please no

 

[MCH]

Hmm interesting, any specific components you can recommend?

Onsemi FSA2276 is small, cheap and has good enough specs.

Agree eARC is at the moment out of reach for the regular DIYer.

I would be interested in complete schematics of your power rails, could you share them somehow? Thanks!

 

[DannerD3H]

cheap HDMI audio extractor with ARC support

Yes, I did also consider this.. Do you know if I buy one of these adapters that actually has volume control(not all does) does that already get integrated in the i2S stream or is it something that happens later in the SPDIF/analog conversion? Would be nice if it was straight in the i2S!

Please no

Hahaha xD I also dont see why I would ever need that..

Onsemi FSA2276

That looks interesting, thaks! Will try that in the next version.

complete schematics

I want to make sure it works first, then maybe yes

DAC and PSU is on their way from china so will know if they work soon!