An Rune integrated preamp, DAC, power amp (for Kickstarter)

[brentsinger]

Hi Everyone. I just wanted to get some feedback before I go to the trouble of launching a Kickstarter.

When I stumbled on Rune my first thought was: "Holy sh*t I've got to build some custom hardware for that". This is what I've come up with:

My proposed circuit board will cost $200, less if I can manage it. I'm calling it 'Kraken' for now so I can make 'release the Kraken jokes'. Name may change. For this you'll get an assembled PCB, 170mm x 140mm, no case for it, and it will not have a power supply. Power supply is always going to divide people and I think it's best left up to the customer, as well as case/enclosure/mounting. I also don't want to get involved in safety issues around AC power. I will keep this project safe DC side only.

Assembled onto the circuit board:
1. A socket for Raspberry Pi.
2. A Wifi module (USB Micro-B).
3. A Bluetooth module for audio profile
4. An micro controller with USB (Device) Audio Profile (through MIcro-B connector)
5. An FPGA module (option)
6. Two expansion sockets with headers/sockets to take either a) An Arduino Shield, b) A PI expansion board, c) an Xbee radio module
7. A PWM processor (TAS5548) 4th order noise shaped Sigma-Delta DAC with Bi-Quads for active cross overs, volume control, a few other nice DSP'ish features.
8. Two TI Class D Power amplifiers, TAS5624A's. These might be configured for 8xSE outputs @ 30W each into 4ohm with <0.1 THD. Another standard option is 2xBTL @60W into 8ohm with <0.02% THD + another 6xSE. The board will be laid out so this is easy for any user with a soldering iron to change quickly.
9. Passive heat-sinking installed
10. Terminal blocks for attaching speaker cables.
11. Banana plugs for power in (14-36V)

The goal isn't to perform at the purist hifi top end. It's about getting close with good bang for buck, and enabling crazy features and development options - invention. I personally have about 20 good loudspeakers I've collected over the past decade sitting here around my desk doing nada. I want to make some novel enclosures, arrays, open baffle designs etc and need to do some correction in DSP to make them stick. This will be a great platform to develop on, drive them HARD, and that will scale into a living room product: being small, media rich, Rune powered and hide-able inside a small case. Wife-acceptance factor is a consideration in my plans.

What you'll get is a compact, cool, energy efficient system that can drive a lot of power with very low distortion into 8 loudspeakers. It's unlikely to need additional cooling or a fan. Crossovers can be implemented active through DSP. Pi-side software will be developed to move the cross over frequencies, and take advantage of other features. The I2S capabilities of the Pi will be used of course. There will be umpteen avenues to expand and customise the features. It should be loud enough to drive your neighbours to daylight psychosis.

Ras PI and Standard Pi Peripherals: HDMI, Ethernet, USB
Runs standard Rune, output to TV, RJ45 to network. Allows XBMC too, and possibly lots of other media applications. The HDMI interface and keyboard/mouse would be used to configure Rune on the device. The socket will be on a board edge so that all the Pi connectors can exit a case.

Break out P6 for I2S DAC operation
No brainer. I2S interface.

Wifi module on board
Integrated wifi module saves you buying another $20 dongle. Just a convenience and it'll be on a separate perk level for those who don't need it

Bluetooth audio input
For smartphones and other bluetooth sources. As above; something that can be cut out to save cost. There are control possiblities through this interface though, and app development would be interesting. An app could be written to use bluetooth to configure Rune to the network, etc. (I can't promise that though, I'm not an app developer.

USB Audio Profile Support
Every system needs a micro-controller for something and with a Cypress PSOC3 we can have USB audio as well. It's likely capacitive touch sensing buttons could find their way into the spec too (on the back of the PCB.) Target would be buttons for on/off, play stop etc.

FPGA Option
Add DSP. Studio effects, distortion, time delays, echos, echo cancellations, more biquads, FIR filters, analystics, resampling, visualisation. I'm keen to use the FPGA outputs with a colour LED Matrix panel like these: to do visualisations.

Expansion sockets
So you can add stuff like:
Or: , or Xbee modules for wireless controllers. The expansion doesn't have to be audio related - electro-mechnical options abound, and you can build your own shield easily.

PWM Processor and Class-D Amp Chips
The numbers are really good. Read here and . A lot of people are anti Class-D but it's a good technology for what I'm trying to do here. Ever since I got a Tripath powered amp I was a convert, and think that Bang for Buck nothing beats Class-D. TI make the best stuff.

Is 8 outputs enough? For phased arrays? Perhaps 16 is a squarer number...


So I'd like to know what you think? Hit or Sh*t? Will you buy one? Is $200 is too much?

[ACX]

Hi Brent, welcome to this forum and thank you for sharing this idea here with us.

I think this is a very interesting developer kit at a reasonable price. I would only put the amplifier board as optional, as some people could not be interested in it (but are in the rest of the package).

Just one question: what are the main reasons that brought you to choose the Raspberry Pi over other developer platforms like BeagleBone Black, UDOO, Banana Pi etc?

So...

[brentsinger]

Yeeeesssss..... we have a mascot for the project.

Hey ACX, Good question. The best reason is that there's a few million in circulation, it's a defacto standard and if I have to start somewhere it's not a bad place. There's also a bit more software development, and a few more projects active on the Pi platform. Performance is less a concern than support and developer depth here.

Don't get me wrong; The RasPi would fit neatly, but any platform with I2S could be wired to that header...

Thanks again to you for all your hard work here. And looking forward to 0.3 soon!

[brentsinger]

I completely forgot to mention that it'd be Open Source FreeBSD 2-Clause, and there'd be a donation to Rune for every unit shipped, at least $10 but I'd like to do more if the numbers support it.

[ACX]

[audiofilodigital]

Fantastic idea, Brentsinger! I also agree with ACX that amp. section could be out of the project. Another important point is that its configuration should be designed with 'newbies' & 'dummies' on mind... Yes, a lot of Rasps have been sold but if you segment the type of clients maybe the total amount of interested Pi users could be not so huge. Obviously Kickstarter will tell the truth about this: market-research, crowdfunding & spread-the-word.
My question is, removing the amplification, how much do you think it may cost?

Regards,


Victor S.

[brentsinger]

So perhaps split the board into two pieces?

Head of Kracken
1. A socket for Raspberry Pi. (Or what ever SBC you like with a wire...)
2. A Wifi module (USB Micro-B).
3. A Bluetooth module for audio profile
4. A micro controller with USB (Device) Audio Profile (through MIcro-B connector)
5. A FPGA module (option)
6. Two expansion sockets with headers/sockets to take either a) An Arduino Shield, b) A PI expansion board, c) an Xbee radio module
Cost about $120.

Tentacles of Kracken
7. A PWM processor (TAS5548) 4th order noise shaped Sigma-Delta DAC with Bi-Quads for active cross overs, volume control, a few other nice DSP'ish features.
8. Two TI Class D Power amplifiers, TAS5624A's. These might be configured for 8xSE outputs @ 30W each into 4ohm with <0.1 THD. Another standard option is 2xBTL @60W into 8ohm with <0.02% THD + another 6xSE. The board will be laid out so this is easy for any user with a soldering iron to change quickly.
9. Passive heat-sinking installed
10. Terminal blocks for attaching speaker cables.
11. Banana plugs for power in (14-36V)
Cost about $120. This would be a low cost clone of the $400 reference design: , with a 2nd TAS5624A. It'll be interesting to compare the two.

The HOK and TOK could stack on top of one another to make a complete system and be sold as separate perks in the Kickstarter.

Just a few questions:
1. Aren't there other DAC boards already on the market that are similar to Head of Kraken? i don't want to copy other products and steal their sales, I would really like to offer something different.
2. Is the FPGA enough to keep HOK different to competition
3. What other outputs do you need on HOK? SPDIF, analog? I could do these with Arduio shield boards.

[brentsinger]

Target would be shipping in October... so 16~20wks. That would include two prototypes of everything. I have most of the IP already, it's just about routing and layout then a lot of testing.

[PhM]

Very interesting project !

I'm currently using volumio/Rune Audio with an hifiberry DAC and a SMSL SA-50 as secondary system (main system is a bit more vintage [Rega Elicit, Rega RS5, TEAC UD501, with Daphile or Volumio / Rune Audio as source)

I use Eltax Monitor III speakers on this secondary system, which make a system a bit below 300€.

When buying it i was also on hifiberry Digi + HIFIMEDIY UD80 amp (http://hifimediy.com/index.php?route=pr ... uct_id=146) solution (no DAC involved which is, on the principle, the base of your project if I understand it).

I think this kind of solution could help to 'market' the price of your project.

What maximum sample frequency do you plan to allow ?

I will look forward on your project evolution and of course on Rune 0.3 .

Philippe

[brentsinger]

Thanks for the feedback Phillipe.

Aside from thinking about Kraken I've been working up to a general Pi dev board called PeX (.) The Kraken was an interlude to consider a more 'application specific' board and what I've worked out tonight is that the two should merge.



I will make The Kraken into 'The Kraken Shield', that can be used on the FPGA PeX or Arduino/Arduino Zero/Maple etc. This will suit people who want to do some DSP, 8 channels to mix, active cross overs, etc, because you really do need an FPGA to do this, or you just can't achieve as much. That little PSoC isn't a DSP processor, and can only really route the audio IMO.

'The Kraken Shield' will have a Pi P6 mating header to tap the I2S lines, and Pi will mate snugly beneath it. I will make sure there's a jumper position to connects channels 1->4 to left I2S, and channels 5->8 to right I2S, then a user can use passive filters for cross overs, etc. This will allow a cheaper, more compact stereo solution for those that don't want the DSP side or want to add extra inputs, shields, etc...

My reasoning is that the original Kraken board would only be $20 (resell) less than FPGA PeX + Kraken Shield, and it'd be less capable. I do think that my killer app for PeX is going to be audio processing and Kraken + Rune is going to sell it on Kickstarter, so there'll be reference designs and tutorials for out of the box operation.

I'm actively developing now, and will post some screen shots as I go. Here is the first, which is the current FPGA PeX protoype design. The concept is that you can add your PI from bottom of the image (it goes over the 'middle' and extends south,) then put your chosen shields and designs on each wing. The wings can be snapped off and mounted above/below, at a right angle, or away from the rest of the electronics via ribbon cable for a front panel application like knobs/dials or LCD. You can also replace a wing with a custom board that has a mating 34 way 0.1" header. This board is planned to be be $100 +/- $20 with a Cyclone IV 22KLE FPGA, SRAM, 16Mbit serial flash. There are going to be stretch goals to improve the spec, one of which is a new higher performance Cyclone V design. The Wifi module will be RTL8188 based and find its way onto PeX as standard, as will the bluetooth module as an option.



It's important to note that I don't want to clone and compete against great products like HifiBerry; I'm trying to do something different if I can. I think that in the OpenSource/Hobby electronics game no one is really making money. We're doing this for reputation and as an outlet for our inventive energy. So it's pointless if you aren't innovating. PeX will complement HifiBerry and other I2S dacs because it could host up to three of them at a time! So you could have Audio Codec Shield + Bluetooth + other shield + Rune -> DSP in the FPGA then 6 channels out through HifiBerry if you like it's numbers better than other DAC options. There a real mix and match opportunity here.

Again, a call for feedback and suggestions?