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Old 4th February 2015, 12:07 AM   #1
DcibeL is offline DcibeL  Canada
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Default Class D amp with I2S input

Hi All,
I am wanting a small amp for use with my minidsp, but want to avoid the extra DAC in between. There used to be a MiniAMP that had direct I2S input and plugged right into the minidsp, however it is NLA.

The only thing I've found so far is the TAS5713 used in the Hifiberry amp, I suppose with some finagling the hifiberry could be wired into the minidsp as well instead of a Raspberry Pi.

Are there any other off-the-shelf solutions for small amp boards with I2S input?
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Old 4th February 2015, 11:06 AM   #2
luka is offline luka  Slovenia
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Some other TASxxxx has PWM input... I input I2s to dsp, which outputs PWM... but it seems to me, you are looking for already build amp, right?
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Old 4th February 2015, 11:20 AM   #3
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TI does have eval boards - but they are not cheap

TAS5760M/MD/L/LD Evaluation Module - TAS5760XXEVM - TI Tool Folder
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Old 4th February 2015, 12:57 PM   #4
luka is offline luka  Slovenia
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well they are, for what they are... but you are far better doing it yourself, getting samples,... If that is not an option, it sure is not the best way to get with eval. boards
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Old 4th February 2015, 01:10 PM   #5
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Mouser has eval boards for the STM STA333IS in stock - $56. Its a 10+10W amp with I2S in.

STEVAL-CCA053V1 STMicroelectronics | Mouser
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Old 10th February 2015, 08:35 PM   #6
DcibeL is offline DcibeL  Canada
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Thanks for the responses. It looks like my cheapest option is the STM eval board at CAD$70ea. Not exactly what I had in mind considering I'd need two for a full 4 channel output and they are fairly low power.

Maybe it is a better option to use a pair of Curryman DACs with external amps. I was hoping that I could have a simple all-in-one solution with MiniDSP and integrated DAC/AMP. I really just wish the MiniAMP was still available.
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Old 10th February 2015, 09:17 PM   #7
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Originally Posted by DcibeL View Post
I was hoping that I could have a simple all-in-one solution with MiniDSP and integrated DAC/AMP. I really just wish the MiniAMP was still available.
You might recognize the right side of this PWB layout: it is that miniDSP piggyback board. But the cool stuff is on the left side. It is an ADAU1701 circuit (basically the same as the miniDSP board) plus 4 nice little power amps. The amps are at the top: there are two stereo SSM3302's. These amps can be run at 15-18V and generate an honest 15W per channel. That's not a lot of power, but by using the ADAU1701 as an active crossover, you get enough crest factor improvement that 15W might be adequate. The board also has two additional analog outputs for a subwoofer or a pair of woofers (using one of the digital output lines from the ADAU1701).

soundbar_amp.JPG

I built up one of these boards but I still haven't tested it. Got the SigmaStudio program for this board ready and it has been tested, but there is still some additional firmware needed. I've got too many projects right now...so stuff is getting done slowly.

There is a "clone" of this board that was done using DesignSpark that will be made available as an "open" design. If someone wants to get a board made, I'll build one up and test it.

The STA333 doesn't look that interesting--an STA350 version would be much nicer. I was thinking about getting one of these to play with, but I'll probably end up making my own design: STA350 pure digital power amplifier board with a coaxial optical fiber USB input 50W+50W 2.1/ 2 support mode. I've built a number of boards with the STA328, so I've got working software for the STA350. The ST amps have some number-crunching limitations (24 bit coefficients), but overall they are nice amps.

Last edited by Neil Davis; 10th February 2015 at 09:21 PM.
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Old 5th March 2015, 10:39 AM   #8
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Hi Neil, please consider the following set of boards :

SPDIF-in to I2S-out (with a SPDIF repeater function)
  • a SPDIF cinch and transformer as digital stereo input
  • a "consumer grade" SPDIF-in chip (WM8504) having no access to the "U" bit of the AES/EBU frames
  • a 6-pin header carrying GND, LRCLK, BCLK, DATA, MCLK as outputs
  • a CMOS-buffered SPDIF dumb repeater with careful cable impedance matching
  • a SPDIF transformer and cinch as digital stereo output

I2S-in filtered STA350 power amplifier (credit-card sized)
  • a 6-pin header carrying GND, LRCLK, BCLK, DATA, MCLK as inputs
  • a 6-pin header carrying GND, LRCLK, BCLK, DATA, MCLK as outputs (passive repeater function to same boards in a multiway speaker)
  • a STA350 configured in "mono parallel BTL"
  • a strap telling the STA350 what audio channel to process (Left or Right or Sum)
  • a 4-pin I2C header enabling a) the designer to program the STA350 filters, and b) the end-user to operate the volume
  • a 4-pin I2C header (passive repeater function to same boards in a multiway speaker)

Remote control receiver (RF type)
  • a remote control receiver (RF type)
  • a Cortex-M0 CPU as remote control interpreter
  • two I2C interfaces for commanding up to four STA350 boards
  • a strap telling the Cortex-M0 if this is stereo 2.0 or stereo 2.1
  • a strap telling the Cortex-M0 if the associated speaker is Left, Right, Sub, Center, Left Rear or Right Rear, or anyting else (8 choices in total).

SPDIF splitter (powered by external + 5V)
  • one SPDIF cinch and transformer as digital stereo input
  • two CMOS-buffered dumb repeaters with careful cable impedance matching
  • two SPDIF transformers and cinch as digital stereo outputs

Let's build a 2.1 system having 3-way Left and Right speakers.

First of all, we attach a SPDIF splitter to the CD/DVD/Blu-ray player SPDIF output. This way we'll have the impedance of the SPDIF transmitters carefully matched (tweaked) to the cabling we are using.

In each 3-way speaker we'll find :
1 x SPDIF-in to I2S-out boards
1 x Remote control receiver (RF type) boards
3 x I2S-in filtered power amplifier (credit-card sized) boards

In the separate subwoofer we'll find :
1 x SPDIF-in to I2S-out board
1 x Remote control receiver (RF type) board
1 x I2S-in filtered power amplifier (credit-card sized) board
Such separate subwoofer gets connected to the SPDIF-out of one of the two Speakers.
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Old 5th March 2015, 03:32 PM   #9
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http://hifimediy.com/amplifiers/read...ital-amplifier

I contacted HIFIMEDIY to see if you could tap into the i2s lines after the USB section of their USB Amps. They said that it could not be done, but they may be producing a i2s or spdif direct digital amp in due course...
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Last edited by dublin78; 5th March 2015 at 03:35 PM.
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Old 5th March 2015, 05:06 PM   #10
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Originally Posted by steph_tsf View Post
Let's build a 2.1 system having 3-way Left and Right speakers.
Been there, done that.

Click the image to open in full size.

Here is a link to a briefing that I gave at DCDIY2009 that explains this amp in more detail. But that was Rev A. Rev D has SPDIF input/output using the WM8805.

The STA350 is actually a lower-powered version of the now discontinued STA326/STA328. There are some minor improvements internally, but the main difference is that the earlier chips had the heatslug facing up, which allowed more output. The STA326 was actually the same as the DDXi-2051, which was introduced way back in 2004. You can still buy the DDXi-2051 from Gerber.

BTW, I have lots of code for reading IR remote controls. But it doesn't take a 32-bit micro to decode a 1-bit stream--it just takes a chip with a good timer module and an efficient interrupt architecture. I actually have code for a number of different IR protocols--this link is a briefing on how the logic works to identify the protocol.
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