2.1 amp with DSP -- preview/teaser

[neildavis]

The capabilities allowed by manipulating parameters are intriguing.
Presumable an optical feed directly from a CD player is an option?
As well as signal taps that bypass on-board amps ( with external amplification in mind ).

Nah--CD players are old-school and just a distribution method for digital libraries . Besides, the 44.1KHz sampling requires an ASRC chip to convert the sample rate, and that adds cost and complexity for a feature that really isn't needed. It makes sense on an AVR, but not for a WiFi active speaker. Same with outputs for external amps.

But yes, being able to manipulate the DSP parameters has some interesting possibilities. Some of the commercial WiFi speakers have EQ, but this speaker will have a 9-band EQ that you can tweak to your heart's delight. And separate volume controls for each driver and customized crossovers. Usually those parameters don't get changed, but it's a "plus" for the uncurable tweaker or for someone building their own active speaker. There will also be a choice of bass enhancement algorithms--that was supposed to be the focus of "Act 2".

The existing GUI is a fairly simple Android app made with the MIT app creator. But if somebody wants to use the more advanced tools such as Xamarin or Android studio or the IOS tools, you could provide a lot more customization. For example, instead of fixed EQ frequencies, the HCI could allow setting the EQ frequencies at any point or using different types of crossovers than what is currently in the menu. I probably won't do this myself, but if someone is interested I could make sure all of the "hooks" are available to extend the HCI.

[Sydney]

Nah--CD players are old-school and just a distribution method for digital libraries . Besides, the 44.1KHz sampling requires an ASRC chip to convert the sample rate, and that adds cost and complexity for a feature that really isn't needed. It makes sense on an AVR, but not for a WiFi active speaker. Same with outputs for external amps.....

How unfortunate ( for my needs anyway ); several times a year I need to do live shows ( this weekend for instance ) - hence the questions
Thanks anyway.

[neildavis]

How unfortunate ( for my needs anyway ); several times a year I need to do live shows ( this weekend for instance ) - hence the questions
Thanks anyway.

I've been looking at upgrading to the ADAU1452 from the ADAU1701, since it has a lot more DSP resources. I've got the ADAU1701 close to fully utilized with this current design, so I will likely make a version of this board with the ADAU1452 in the near future. The ADAU1452 has integrated ASRC circuitry, which would make optical inputs "easy". The board outputs use RCA connectors, and I'll continue to use them as it makes using different amps a lot easier.

[ernperkins]

Oh, the seductive nature of adding features until the project becomes a constantly moving window. Program managers at work had a saying: "sometimes you just have to shoot the engineer".

[Sydney]

I've been looking at upgrading to the ADAU1452 from the ADAU1701, since it has a lot more DSP resources. I've got the ADAU1701 close to fully utilized with this current design, so I will likely make a version of this board with the ADAU1452 in the near future. The ADAU1452 has integrated ASRC circuitry, which would make optical inputs "easy". The board outputs use RCA connectors, and I'll continue to use them as it makes using different amps a lot easier.

Looking forward to it, Carry on

[neildavis]

Oh, the seductive nature of adding features until the project becomes a constantly moving window. Program managers at work had a saying: "sometimes you just have to shoot the engineer".

Actually, a bigger problem than creeping requirements is the furious pace of consumer electronics technology evolution. A previous version of this board had an ASRC with SPDIF inputs, but that was before the current generation of WiFi products. I was using the SPDIF stream to send messages in the User bits. But that approach is OBE with Bluetooth and easy to use Android software tools. I've been working with DSP processors and class D amps for at least 15 years now, and I've watched one chip after another become obsolete, and in one case before I even finished laying out out the circuit board! Fortunately, we are at a time in the technology evolution where most of the technologies have become "good enough" and there might not be as many rapid changes as before. At least, that is what I'm hoping is the case .

[neildavis]

Hmmm...my wife has a stereo pair of Heos HS1 speakers, and the Dayton app sees them and will route audio to them. Also, I can route audio using the Heos app to the Dayton module. I'm impressed. I doubt that I could do that with the Sonos or Bose wireless speakers, but it will be fun to try next time I'm visiting our daughter, who has a couple of the Sonos speakers. If all or at least some of these new wireless speakers actually play together nicely, I'll be flabbergasted.

[Sydney]

...and will route audio to them. ...

If it could route into a Yamaha M7C Mixer,,,I'd be delighted

[djkest]

As I said, there are two versions of this project. The second one has a very interesting tweeter arrangement with a passive crossover at 5000Hz. Hint: what tweeters remind you of zebrawood?

AMTs?

[neildavis]

AMTs?

Of course . I couldn't get the image out of my head once it got stuck there. I already had the small ones but had to buy the bigger ones. I wish I could have found a woofer the right size with a copper phase plug, but it wasn't to be.



This project is still moving along, although there have been lots of hiccups. One problem that had me stumped for a while was lots of strange digital noise coming from the WiFi module. Not super loud, but annoying. I tried a number of different grounding schemes, and the only thing that worked was isolating the ground and power for that module. I need to do some more testing with isolating DC-DC converters to finalize the next iteration of the design, but at least I know what the problem is.

Given the way the challenges unfolded, I had to rearranged the project write-ups. Act 2 will be the plate amp itself, and it's many challenges. I'll probably start that write-up next week.

Act 3 will be the "turn-key" software, including the smartphone controller. That's coming along OK, also. I can control the volume levels of each channel and the upper and lower crossovers from my cell phone, and I'm debugging the EQ. I should have most of the basic DSP functions and Android control done this week.

Act 4 will be the bass enhancement algorithms and other extensions, and that will be deferred until a later time. Act 4 is where this project gets really interesting to a hard-core DIY'er, as it will address how to modify the DSP and get the most out of the speakers. It will show how to use different ADAU1701 algorithms, how to get that code into the micro, and how to add new controls to the cell phone software.

[Millstonemike]

...One problem that had me stumped for a while was lots of strange digital noise coming from the WiFi module. Not super loud, but annoying. I tried a number of different grounding schemes, and the only thing that worked was isolating the ground and power for that module. I need to do some more testing with isolating DC-DC converters to finalize the next iteration of the design, but at least I know what the problem is.

Lots of digital noise in the area with the switch mode PS and the amp itself. Digikey has a number of chip based isolated DC-DC converters. Most of the reasonable priced units don't put out a lot of power (~100ma + IIRC).

Nifty way to mount the amp to use the AL plate as the heat sink. You shouldn't have a problem there.

Not to worry, the physical wiring is good. The only time I've seen better is by a guy who builds old-school tube amps for guitarists. But it's his business and he does it every day on repeated designs.

[Sydney]

... Act 2 will be the plate amp itself, and it's many challenges. I'll probably start that write-up next week.

Act 3 will be the "turn-key" software, including the smartphone controller. That's coming along OK, also. I can control the volume levels of each channel and the upper and lower crossovers from my cell phone, and I'm debugging the EQ. I should have most of the basic DSP functions and Android control done this week.

Act 4 will be the bass enhancement algorithms and other extensions, and that will be deferred until a later time. Act 4 is where this project gets really interesting to a hard-core DIY'er, as it will address how to modify the DSP and get the most out of the speakers. It will show how to use different ADAU1701 algorithms, how to get that code into the micro, and how to add new controls to the cell phone software.

Did you set a time frame for Act 4?

[ani_101]

ACT 4.... Waiting for it... !

[neildavis]

Lots of digital noise in the area with the switch mode PS and the amp itself. Digikey has a number of chip based isolated DC-DC converters. Most of the reasonable priced units don't put out a lot of power (~100ma + IIRC).

Nifty way to mount the amp to use the AL plate as the heat sink. You shouldn't have a problem there.

Not to worry, the physical wiring is good. The only time I've seen better is by a guy who builds old-school tube amps for guitarists. But it's his business and he does it every day on repeated designs.

The grounding isn't ideal because there is no easy was to electrically isolate the amplifier from the chassis/plate. The mounting holes are connected to the amplifier ground plane, and in order to get a thermal transfer from the heatsink to the mounting plate I needed to use 20mm threaded standoffs with a .5mm thermal pad. The analog input connectors are isolated from the plate, and there is no noise at all when the analog inputs are used.

But the antenna ground isn't isolated from the plate, and that is probably an issue. I haven't tried isolating the antenna yet--that might also work. The noise appears to be related to the networking RF signals--there is a lot of random activity in the noise. When I powered the module from an AC-DC converter (USB charger), the noise went away completely. I bought some DC-DC converters and will try them next. I need up to 300ma for the WiFi module, but there are a lot of small 2W converters to choose from.

I have three switching power supplies in there, plus the 6 channels of class-D amp plus the DSP, so there's a lot of noise getting generated. But it is that WiFi RF amplifier that is being unsociable.

[neildavis]

ACT 4.... Waiting for it... !

I already laid a foundation for Act 4 with that series of articles on the Audiodevelopers web site. But there are still a lot of details and examples, and that will be coming soon, along with the PE SBDT write-ups. What may take more time is extensive experiments with the various bass enhancement algorithms. There are a number of algorithms that ADI has available, but testing them and tweaking the parameters and evaluating the results could take a while. If someone wants to help, this could get done a lot quicker. I've got extra hardware that I could give away to someone willing to test and evaluate.

Honestly, I'm still agonizing over how much code I really want to put in public domain, because some of this might be marketable, and my son is looking for opportunities like that. But I will give the code to any person who asks for it.