600W Class D TAS5624A Amp, with USB, HDMI, Bluetooth, and RasPi for Network Streaming - diyAudio
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Old 1st July 2015, 08:33 PM   #1
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Default 600W Class D TAS5624A Amp, with USB, HDMI, Bluetooth, and RasPi for Network Streaming

Hi, I've had this project on the cards for a long time in my spare time. I'm a professional engineer working in Industrial and Defense electronics in my day job, but I've always wanted to make hifi amplifiers. I'm from somewhere between Gen Y and X, so I've been on a digital only diet my whole life and have never really been interested or convinced by escoteric analog arguments. And I'm usually pretty broke. My budget is actually quite pathetic.

I'm calling it the Kraken Amp for now. The 8 armed tentacle monster. It's nearly done.

So my goal here is to:
1. Make a 600W amp that can drive 8 single ended loudspeakers, or 4 in BTL, or a combination of both.
2. Make it digital only with really high PSRR, snr and no loss in analog stages
3. Make it a hifi in a box style of product, so that it can be used in a lot of situations like home entertainment, not a hifi only setup
4. Make it stream. UPNP, Spotify, Internet Radio, etc
5. Make it inexpensive and compact, leverage technology, find 'sweet-spots' and use tricks to achieve cost goals.

I hope to Kickstart later this year, but can you please give me your opinions. Hit or sh!t? How do I make it more appealing?

600W Class D Amp

2x TAS5624A's driven by a TAS5558 Sigma Delta modulator. The latter is important because the algorithms therein are magic. The 5558 has 8 outputs for two 5624A's. Each of these quad H bridge parts drive an 8ohm BTL load 150W @ 10% THD, 70W @ 0.1% THD, 60W @ 0.02% THD. Passive parts and design are taken from a reference design.

Power Supply

Class D Amps have great power supply noise rejection. Its a huge advantage over traditional designs, but to make it better Kraken has it's power split into four channels, two for each 5624 chip. Each has it's own path, so there is less interference between channels. Each path has it's own terminals, reverse polarity protection, over voltage protection to 70V (20~42V is nominal input), inrush protection and over current protection. An LDO in the path regulates a dirty input providing +60dB ripple rejection, and passives including a large common mode choke provide another 10~40dB depending on the frequency of interest. Combined with the PSRR of the 5624's @ >64dB power quality should be superb.

What's the point of so much ripple rejection? That lets you use a low cost supply like this one: LS150-36 for $37 per channel, or $148 for a 600W total solution. And it should be completely silent.

Click the image to open in full size.

Digital Only

Bluetooth audio from Andriod, (iHope) iPhones, and other BT sources, USB Audio, HDMI Audio instead of analog inputs (perhaps pass through but that's a bit harder,) PCM/I2S through a discreet connector, and... a Raspberry Pi. The latter has I2S output and out-of-the-box projects like Rune Audio give you a web interface from your Smart Phone. You can use your browser to any stream any internet or network source to the system - like Spotify which supports HD Audio streaming. I've tested the system with Rune and Volumio and the I2S playback works well. With some software work it could be seamless but I have to convince those guys to support me too.

No SPDIF? HDMI seemed more of a future proof choice and has superior audio bandwidth.
No Analog? Again HDMI can be found on every CD, DVD, Blu-Ray source and our lives are so Smart Phone oriented now that these seemed appropriate. Using a laptop or PC as a HD Audio source is possible through USB Audio and everything is asynchronously resampled. I think that people who love their analog are not going to buy this system, so I'm not going to slow the project trying to support everything/everyone.

More than one Kraken can be daisy chained, so if you want more power, you can use one for each cabinet. Phased array systems are possible this way too, but the system doesn't have the DSP capability to delay/store a signal. Because it accepts a discreet 3.3V or 5V I2S/PCM input, there is no reason why you couldn't connect it to any FPGA or DSP system for doing this sort of fun work.

Click the image to open in full size.

Inexpensive

The goal is $400 for the base mode on Kickstarter.

The class D components are affordable, and only demand reasonable sized passive parts. The design is uncomplicated and made from commodity parts on a modest 4 layer circuit board. The design will have a few surprises to drive down cost in other ways, but I won't mention them until I've finished testing and know they are production ready.

It's a cheap amp, but the real cost saving in your system is:
- a really low cost power supply solution
- allows active cross overs - no expensive cross over components
- no pre-amp, it's a single box solution
- good use of your phone and internet streaming of HD Audio, reducing source cost

Because you can have 4, 6 or 8 outputs in this system, and because each can have its own biquad filter, active cross overs can be achieved. This can all be achieved through software setup either through USB or (I hope) through a web interface when a RasPi is fitted.

I especially want this product to appeal to guys making their own cabinets and OB designs, and intend it to be inexpensive enough to experiment with, and embed in a cabinet design.

Click the image to open in full size.

Please let me know your thoughts and suggestions. Prototyping in August at this rate. thanks, Brent.
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Old 2nd July 2015, 02:29 PM   #2
von Ah is offline von Ah  United States
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Quite ambitious! Look forward to your progress.
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Old 2nd July 2015, 03:06 PM   #3
Speaky is offline Speaky  United States
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Hi,

I've seen your design elsewhere and i'm pretty interested in doing the same kind of thing. Here's what I see, though...

First: I want analog input. I understand most sources are digital but the only output is analog for all sort of things that I may want to hook up. For example, I've got a media room with a 7 channel receiver and 7 speakers that I can't connect to it?

Second: this is way too much money. I can go to Amazon and buy the equivalent pieces for under $200 so paying $400 for a single board with less versatility is a non-starter.

Third: most speaker systems (mine included) use tweeters, mids, and woofers - each with their own power requirements. Using a high powered amp for a tweeter seems like a bad thing - your noise floor will be higher than it needs to be and the sweet spot for distortion is too loud.

Fourth: if you're running Bluetooth etc into the I2S then there's no control. How do I remotely set the EQ for this system? One of the huge pluses of a complex electronic multiamp is real-time control over the crossover and eq curves. I think this needs a processor.

Just my first thoughts.

Mark
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Old 2nd July 2015, 05:09 PM   #4
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A pure digital amp might be the cheapest solution, theoretically. Practically digitally PWM is multiplied with power supply voltage as the "DAC reference". Thus you need a very clean power supply to obtain noise margins of 100dB or more.

Last edited by voltwide; 2nd July 2015 at 05:18 PM.
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Old 3rd July 2015, 05:49 AM   #5
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Hey Speaky, thanks for your reply. All good points.

Quote:

First: I want analog input. I understand most sources are digital but the only output is analog for all sort of things that I may want to hook up. For example, I've got a media room with a 7 channel receiver and 7 speakers that I can't connect to it?
There are two PCM/I2C ports to external equipment, for expansion or daisy chaining amps. One is marked Input and the other Output, but they have both channels on 3.3V signals (not ethernet) over an ethernet connector, for standard cat5 eth cable. This is because everyone has them in their draw, so I'll use them off label for expansion.

The great thing here is it lets you design an analog board that plugs in. I was thinking a Wolfson WM8731 stereo analog to I2S would be my first trial. I was also going to use these ports to add a control panel with leds, dials, buttons, etc, but anyone can make a quick board.

Another important thing - this is going to be open source. I'll release the schematics and circuit board in Altium format, as well as the software for the PSOC processor. The RasPi project i talk of: rune and others, are all open source and well supported.


Quote:
Second: this is way too much money. I can go to Amazon and buy the equivalent pieces for under $200 so paying $400 for a single board with less versatility is a non-starter.
You are right, but there are many surface mount parts to achieve a design like this. A lot of the cost is in the 4 layer PCB and the assembly, but also the cooling design, etc, that allows it to be very compact. $400 was including all assembly of all parts + testing, but I'm wondering if I can offer the raw PCB for sale too... I would not want to support it though, as you'd have to be a soldering ninja to put it together without failure. It's very integrated and busy.

The model for pricing is cost +70%. So I'm expecting my finished board (parts, PCB, placement, packaging, & don't forget testing) to cost $235. The 70% is insurance in case things go wrong, cost of money, some of my time as I'd have to take time off work to fulfill the orders, etc.

Being open source, you can absolutely go and make the design yourself from my files, but if I can Kickstart a 100 or so boards together, there is bulk advantage.

Quote:

Third: most speaker systems (mine included) use tweeters, mids, and woofers - each with their own power requirements. Using a high powered amp for a tweeter seems like a bad thing - your noise floor will be higher than it needs to be and the sweet spot for distortion is too loud.
Not sure I accept this one. Remember that the sources are all digital, so there is optimal dynamic range and (should be) no noise floor from analog sources. Equalisation and low sensitivity tweets might be necessary - it's going to take a listening test I think. Running these class Ds at lower power means very low THD - 0.02% for this part.

I'm planning it to support two cabinets, each has a BTL + 2x SE. 150W for sub, 75W mid, 75W tweet. The latter is overkill, so volume control is necessary. Active cross over biquads on each channel, no passives.

Quote:

Fourth: if you're running Bluetooth etc into the I2S then there's no control. How do I remotely set the EQ for this system? One of the huge pluses of a complex electronic multiamp is real-time control over the crossover and eq curves. I think this needs a processor.
That's all covered. It has a PSOC3 (or PSOC5LP if needed) on board. This part handles USB Audio, programming biquads/settings through USB, plus all the house keeping. Control can come through RasPi as well (but the system can work without RasPi) through web interface and I'm talking to some folks about support for Kraken. Either can be used to program the biquad filters in the TAS5558. These allow all active crossovers, volume control, mute, equalisation that you like. I have some plans for control, but will hold off announcing them in case they don't work. Needs testing.

The psoc has some light dsp capability even (beyond programming the TAS5558 that has extensive DSP), but what it won't allow is delay lines for making a phased array. I'd have to add SRAM here and I'm out of pins for parallel, and I've not done the math to see how hard a serial SRAM solution would be - I'm going to wait and see if there's a request/requirement before spending this time.
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Old 3rd July 2015, 06:08 AM   #6
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Quote:
A pure digital amp might be the cheapest solution, theoretically. Practically digitally PWM is multiplied with power supply voltage as the "DAC reference". Thus you need a very clean power supply to obtain noise margins of 100dB or more.
Voltwide, that's not completely true. The Class D's get so much PSRR - power supply rejection ratio - because they switch around 400kHz. At this frequency the ear can't hear the quantisation noise from the sharp edges. That said, the power supply noise gets through the H bridge of the class D chip, but is reasonably squashed by the demodulation filters - ie. the big passive LC filter on the output - and the filtering you put before the class D chip.

That said, there's a lot of additional filtering and insertion loss in each power path to turn a bad supply into a good supply. This includes active regulation that has >60dB rejection of noise at all audible frequencies. 60db means 1 millionth of the noise gets through.
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Old 3rd July 2015, 07:44 AM   #7
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Quote:
Originally Posted by brentsinger View Post
60db means 1 millionth of the noise gets through.
No, 60dB is 1:1000.
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Old 3rd July 2015, 12:13 PM   #8
Speaky is offline Speaky  United States
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Hi Brent,

I've been going through a build-buy cycle and I'd love a single board solution but here's what it has to compete with. This is one of my possible builds:

WiFi/Ble USB - $15
Cirrus logic Audio Card -$40
Rasp Pi 2 - $40
4 x irs2092 250w - $120. At $30 each aliexpress

This gives me 24 bit 48,96,192 analog input
Spdif I/o
5 band eq crossover in chip
Plenty of HP for the pi2 to do audio processing
Ble 4 input
WiFi direct
Web server
Spare USB port

Total $215

Many of these features I find compelling. Linux on the crossover... sure.

Mark
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Old 5th July 2015, 09:44 AM   #9
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Quote:
No, 60dB is 1:1000.
Pardon me, you are correct. 1:1000000 would be for power. 1:1000 for voltage attenuation is correct. I still think that's pretty ok :-)
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Old 5th July 2015, 10:56 AM   #10
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Mark, you are right of course. You can do the whole project cheaper, but you are probably not my target market. The guys I want are building cabinets and playing with active crossovers, etc. You sound capable of putting the electronics together as well as I am, and clearly you know your purchasing choices really well - but will you get any time left over to design a cabinet? I'm guessing you already have the speakers but are looking to improve your system through a better amp.

I looked at the Cirrus card for integration and inspiration, but thought it was a tool for DSP and recording on the Pi so left it out. The Pi in my system is a streaming source, an accessory, and not the centerpiece. It might end up being the best place for control software.
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