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

[gswg]

Or why not try the respected (www.iqaudio.com) Pi-DAC with on-board hardware volume control. No pre-amp needed

As a heads up, IQaudIO Pi-AMP's have arrived and are under test for the next week or so before we sign them off and go into full production. The Pi-AMP sounds really expressive, open, tight and fast - even when being driven by a simple 12v 1.5A power plug.

Together, with the Raspberry Pi, the Pi-DAC & Pi-AMP, combined with RuneAudio or your other favourite distribution delivers a complete one box solution - just add speakers.

We will be selling some of these initial Pi-AMP units as evaluation models to interested parties. Get in touch on the email below for more information.

Gordon@iqaudio.com

[brentsinger]

Groannnnn.....

There are too many DACs. I can't tell which is best, but anyone with a nice amp going to be well covered by the current DAC selection. My problem is I don't have a nice amp! So I'm building one that takes a Pi I2S inputs

Working well so far, the I2S output can be seen running from P6 -> My FPGA Dev board -> to a Audio Codec Board (Wolfson WM8731.)



Worked first time. Sounds good so far, no distortion I can hear.

Now I'm going to lash up the Class-D evaluation module that arrived this afternoon. 200W per channel.

[NullDev]

Just to throw another idea in the mix, the is a USB to Class-D amp. The USB portion isn't that interesting, but once the audio is converted to an I2S stream (Savitech SA9023) it's then directly fed into the Class-D amp. There is no DAC in the chain. They use STMicroelectronics STA335BW which converts the I2C to PCM and then directly drives the FETs with this signal. I initially wanted to design this myself, but it's hard to pass up if someone else already did it for $79. I have one hooked up to a BBB and it sounds fantastic.

[brentsinger]

Thanks for the suggestion. I like HifimeDIY. It's a nice product and at a very solid price point so everyone can enjoy it. It would be great as a full range driver for book shelf speakers.

What I see that can be improved on:
1. HifiMeDIY has 0.2% THD at 1W 1khz power out.

The numbers on the TAS5624 are better; 0.025% THD @ 1W 1khz. The latter will do 70W per channel x2 channels before it reaches 0.1% THD. This is because TI are good at sigma delta converters. They use a 4th order sig-delta modulator dac (to modulate the power FETs) that runs at a very high frequency. The high frequency (low MHz range) means that all the signal path quantisation noise and error from digital signals is 'pushed' up past our hearing range. The driver chip FETs are finally driven by a high kHz (about 400kHz) output, and all the quantisation noise (all the THD) is way beyond our hearing, again no audible error. This makes sense when you think about it because all the digital edges are really sharp and fast and their harmonics are high MHz, beyond our hearing. I tried to make a sigma delta DAC on an FPGA myself and failed - it's serious DSP and really hard to get right; but this is TI's business and they are very good at it.

2. Only two channels means you need either a) full range speakers, b) passive cross overs.

I think that active cross overs are a huge cost saving, and can sound better. With actives you get a viciously sharp filter roll off, and can control to a fraction of a Hz where the filter is. There is nill power loss too, so less heat is generated in your amp. The Kraken I'm working on will have either 8 outputs or 6 - 2x 200W + 4x 100W ea max power, or 0.1% THD @ 2x 100W + 4x 30W ea on a 4ohm load. So you can have a stereo three way system this way with 100W bass/sub, 30W mid, 30W tweet on either side and no passive cross over components. The $200 you save can go towards a 2nd Kraken

Personally I want to put two Krakens on a Pex motherboard and drive an array of 16 low cost speakers in an open baffle. It's great just to screw around with something like this. Opens up fun possibilities.

3. Where do I plug my SBC in?

Kraken will be a different product, with equivalent sound but more channels, power and cost. It'll be about 2x expensive, but I'm not there yet to say for sure. Kraken will be able to drive big complex systems. I hope.

[Freddy]

Hi

Kraken sounds like a great project.
When can it be purchased?

I also found another Raspberry Pi amp under development

http://audioberry.com/projects/raspberry-pi-amp-update/

No idea of its cost and availability

Freddy

[brentsinger]

Those ICE Power modules he's using look great... they have the power supply integrated which is important. I think that his project is all about the casing and finish of an amp appliance, where as I'm looking to sell my system to people just like this guy who will go and embedded it into a finished appliance.

I've looked at designing in a supply but I though it would blow the project out beyond a year. The problem also is that would be second guessing what people are going to do. If you have 8ohm or 4ohm loudspeakers, or depending on the application/installation your power use could be really different , so I thought people would do best to buy a supply - test a few even - to suit their installation. Kraken should be able to run from a 12V car supply too, but won't have too much juice in that case.

The work is coming along slowly and the CAD has started, but I've had a dud EVM module come from Texas Instruments. The suggested fix is to remove and replace a chip - not an easy rework but still quicker and easier than sending it back. TI fail.

[bienaime]

This is an interesting project, I hope to keep an eye on it.

[brentsinger]

Thanks. I hope to get it finished before Christmas! Damn day job getting in my way!

I'll post some more screen shots as things firm up. Latest change is RasPi B+ support, and I may just shoot for a Max 10 FPGA instead of the Cyclone IV FPGA module that I'm currently using.

[brentsinger]

So after a lot more effort than I expected I have the bare bones of the system working. The TI chips I'm using had some 'quirks' and I got some bad advice from their FAEs that really sent me down the wrong path; but after persisting I've got a Model B Raspi pumping out 300W into some bookshelf speakers and they sound great. I need to do more listening tests on bigger loud speakers asap.

To revisit the idea, the Kraken system is a headless MPD player (Rune), then I2S all the way to the power stage which is a Class D setup. Analog doesn't feature anywhere. User just need configure Rune and add loud speakers. I've got an analog/RCA input, a USB audio input working, and plan a HDMI (passthrough) audio stripper. I'll consider TOSLINK and/or SPDIF if advised, but I feel that audiophiles will not want this system. Those guys hate Class D; I think it's misguided, but will defer to their better ears. Regardless, Kraken wants to be a very practical, convenient system, best for and embeddable in DIY projects, and cheap enough to installed many times in your house. Bang for buck audio quality, and usability and the goals. I'm planning controls that can be operated by my 4yr old who loves music.

It's an asynchronous system, with a sample rate converter that upsamples inputs to 88.1/96Hkz, or 192kHz depending on the number of channels you want to process. Each channel has a few biquads, making active crossovers possible. That's my choice now; to choose the number and makeup of the power output channels. My options:

- 8x 75W channels
- 2x 200W channels + 4x 75W channels
- 1x 400W channel + 2x 200W channels
- 2x 400W channels

Or some other combination. There is a formula: the system will have 8 'lanes'. A 75W channel takes 1 lane, a 200W channel takes 2 lanes and a 400W output consumes 4 lanes. Any combination has to add up to 8 lanes.

What combination is going to be most useful? I'm thinking all of them, but I can't decide where to start.

[ACX]