Full digital amplifier with chip STA326

[zek]

you can pick up a STA326 chip amp for USD65 on eBay.....

Link please.
Thanks

 

[Kjeldsen]

STA326+PCM2706+AK4113 OLED 2.0 Class D DC24V 32V Digital Stereo Audio Amplifier 2x50W USB / optical / coaxial input 24BIT/192K-in Amplifier from Consumer Electronics on Aliexpress.com | Alibaba Group

 

[CharlieLaub]

STA326+PCM2706+AK4113 OLED 2.0 Class D DC24V 32V Digital Stereo Audio Amplifier 2x50W USB / optical / coaxial input 24BIT/192K-in Amplifier from Consumer Electronics on Aliexpress.com | Alibaba Group

Note that, if this uses the PCM2706 USB RX chip as claimed, then it can only support a max format of 16bit, 48kHz via USB and 24/192 audio is only via the coax/toslink spdif inputs.

Also, with 4R speakers and 30V PS you can really only get about 25W before THD shoots up, and below 25W THD is around 0.1% for any power level. This is better used with 8R speakers - THD is lower and power can reach 50W before clipping.

 

[zek]

What is the best USB chip that supports a resolution of 24/192 (XMOS or something new)?

 

[TNT]

DAC chain:
Digital PCM -> DAC -> Analog -> Class D AMP ADC -> PWM -> Speakers

Digital chain:
Digital PCM -> Class D AMP PWM -> Speakers

There are some alternatives with optical input like Chinese amps with STA326 chip.

There is no ADC in a class D amplifier. Hence, a class D amplifier is not "digital".

//

 

[theaspin]

Correct, what I meant is the part that converts analog signal to PWM.

 

[foxint]

Hi Guys

Thank you. Still very confusing....I have found a few (only a few) reasonably priced digital only (with no ADC/DAC) with digital only input. So that is good....but this is a situation that stumps me....

If I wanted to make an active 2-way speaker system (as I have using old school analogue stuff)…..
· source – DSP – 4 digital outputs
1. High Frequency Left channel
2. Low Frequency Left channel
3. High Frequency Right channel
4. Low Frequency Right channel
· How do you connect to a digital AMP?????

Most digital only amps have one 2-channel input (albeit RCA, USB, Optical)…So how??

I would have imagined like analogue amps, there would be a right channel and a left change. Or a Mono (single channel) amp

But I cannot find anything.

Can you help – suggest

 

[Neil Davis]

Most digital only amps have one 2-channel input (albeit RCA, USB, Optical)…So how??

The "integrated" amps are only 2 or 3 channel (2.1), but there are a number of multi-channel PWM controller chips that can be used for making multi-way active speakers. The controller chips require a separate power stage, which can be done with one or more additional chips for the H-bridges.

It's interesting to look at how old some of these designs are. The STA326 is actually the same as the Apogee DDXi-2051, which came out in 2004. ST was the fab house for Apogee, and they retained some of the rights to sell the chips after Apogee went bankrupt. The multichannel controller chips actually preceded the DDXi-2051--they were released between 2000 and 2003. ST has made some improvements to those early designs in recent years, but most of the enhancements are relatively minor. The TI multichannel controllers were based on the Toccata designs, which TI acquired in 2000.

An example of an ST multichannel controller is the STA309. The comparable TI part is the TAS5508. Either of these chips can be used to make multi-channel active speakers, and both devices have enough DSP "horsepower" to implement the crossovers. The picture below shows an interesting 5-way speaker based on the STA308a (The amplifier is a modified Spherex 5.1 amp, mounted in the back).

 

[foxint]

Hi Neil

Excellent thank you. Thanks for the history lesson.

I have aspirations way above my technical abilities.

So to dumb it down how to I make a multi-Channel 2-way active speaker system with a digital amp…. I have this set-up with all analogue components.

So how does one actually attach say 4 channels (HF-Left; LF-Left; & HF-Right, LF-Right) to a digital amp…. are there any digital ONLY amps with single channel inputs…i.e. can I buy say 4 mono (single channel Digital Only amps)??????

 

[assichevi]

Solution is to use DSP as crossover (miniDSP nanoDIGI 2x8 for example) & STA326/328-s as amplifiers. Problem is you'll need to control volume on STAs simultaneously, so separate MCU & software will be required.

 

[assichevi]

... Also, with 4R speakers and 30V PS you can really only get about 25W before THD shoots up, and below 25W THD is around 0.1% for any power level. This is better used with 8R speakers - THD is lower and power can reach 50W before clipping.

Strange logic. How do you plan to get more power on 8R load than on 4R with same supply voltage? Simple P=U^2/R says opposite.

P.S. i do aggree that 8R speakers are better for small digital amps as current through output filter & output MOSFETs is twice lower thus THD is better.

 

[Neil Davis]

So how does one actually attach say 4 channels (HF-Left; LF-Left; & HF-Right, LF-Right) to a digital amp….

You will probably have to write code for a microprocessor to do what you want. The STA326 is intended to be used with a micro--in fact, the default state of the output devices is "off" at power-on, and you need to write to the appropriate register via the I2C bus to get the chip to output audio. But once you figure out how to program the chip, you will be able to route the digital audio, load biquads to implement the crossovers, and use the other resources in the chip--the volume, DRC, tone controls, etc.

The Arduino micros would be fine, but it takes a while to write all of the code you need. I've got lots of code for the 68S08 series chips that control the STA326, and it could be "translated" to C++ for the Arduino rather easily. But no, there is no "easy" way to make these chips useful for building active speakers.

I've also got PC code (.NET) for calculating the coefficients and for communicating with the micro that controls the STA326. That way, you can model the response, starting with driver measurements and then reprogram the DSP in the STA326 in real-time. The code I've got started out as a way to program the now-obsolete TAS3004 DSP, and also works with the STA32X and STA308/309 chips, as well as the ADAU1701 chip.

As someone else pointed out, one of the challenges with the "all-digital" signal path is implementing the volume control, so that both left and right speakers track each other. My solution to that was to add messaging to the SPDIF data stream. The SPDIF standard provides 2 user bits per frame for signaling, so you can send out volume, routing and other messages to both left and right speakers from a properly designed preamp. But the code to do that is fairly complicated.

The picture shows an STA326-based amp that I made many years ago for active speakers.

 

[foxint]

Gentlemen

Excellent answers. Thank you for your time. I have aspirations way above my technical ability. While I have all this equipment as analogue and it works and it is good....I would like to move on.....

"use DSP as crossover (miniDSP nanoDIGI 2x8 for example) & STA326/328-s as amplifiers. Problem is you'll need to control volume on STAs simultaneously, so separate MCU & software will be required"

I know about the miniDSP nanoDIGI 2x8.....but the other stuff is way above me....can some show/explain as if I am a 5-year old.

Surely I am not the only one who wants to do this??? I am surprised it is not easy to get the gear.

????

 

[Neil Davis]

Surely I am not the only one who wants to do this???

It's a good question. I asked an Apogee tech rep many years ago a similar question, and he too thought it odd that the chips weren't being used for multiway active speakers. But that was probably around 2005, and it was well before Arduinos and other easy-to-use micros. So it was really only those pathetic geeks who programmed in assembly code or else big companies with the microprocessor development systems who found these chips exciting. Still, I expected that someone would have tried marketing active speakers with class D amps and embedded DSP, as it is a high quality solution with a relatively low cost to implement.

You might find this briefing interesting. I gave it at a DIY gathering in 2009:
http://www.audiodevelopers.com/temp/DIY_Crossovers.ppt

If you don't have PowerPoint, I can format it differently for you.

 

[foxint]

Neil

Thank you. Again excellent responses, a little (lot) over my head. I read the ppt and it was great, but a little above my understanding.

From what I understand (and other reading) most of the DSP can be done on a PC, then outputted to various “digital” amps.

But the problem I see (Ok may have missed it) but the connection mediums. How does one get say for the sake of ease 2-way active speakers…the 4 digital signals from the PC to the amplifiers then the speakers.????

From my reading all (most all that I have seen) digital boxes (DAC, amp) only have 1 (various – RCA, AES, optical) input that runs into the chips (all stereo) then it all gets thrown out as 2 channel analogue.

If there were mono – boxes this may solve one of the problems?

Unless the PC can spit out say 2 channel (HF & LF) for the left via RCA, AES or Optical one cable and then another for the right.

Or am I being too simple????

There are so many plug and play solutions but NOT for active speakers….

I am no electrical engineer nor good with DIY soldering….

This is how I do it in the analogue pro-audio:

I am very confused…. I can do this very easily in the analogue world:

· Source – PC or Raspberry Pi3 into
· DAC into
· Aphex – signal processor into
· dBx graphic equaliser into
· dBx electronic cross over into
· 2 stereo 100-watt ART amp into 4 outputs
· Everything have XLR speakers have Neutrik SpeakON connections

Easy…. Each component has discrete channels – 2 inputs and 2 output (except DAC that has only 1 input and 2 analogue outputs). The crossover has 2 inputs and 4 outputs.

See my confusion??? What happened to the digital experts….?

 

[Neil Davis]

But the problem I see (Ok may have missed it) but the connection mediums. How does one get say for the sake of ease 2-way active speakers…the 4 digital signals from the PC to the amplifiers then the speakers.????

In the active speakers described in the briefing, the crossover is actually in the amplifier, or else on another circuit inside the speaker. So you only need an SPDIF input that has left and right channels, and the SPDIF goes to both speakers with a simple splitter. The left speaker extracts the left channel and the right speaker extracts the data for the right channel. The DSP inside the amplifier splits the digital audio into the desired frequency ranges. Usually this is done with biquad filters. The outputs of the DSP are then routed to the PWM modulators and the PWM signals drive the power amp stages. All of this happens inside each speaker. And in the case of a chip like the STA326, all of the crossovers, routing, PWM modulation and power amp stages are inside the amplifier chip! So there is just one input from the PC--the SPDIF signal.

It is also possible to have the DSP external to the speaker, and you can also have the amplifiers external--in fact, that is the way most DIY'ers do it. But then that creates the problem you describe--with 4 or more signals going to each speaker, or else lots of speaker wire (wives hate that). I much prefer having all of the DSP and amplification inside the speaker. That's the way commercial active speakers are designed, and it is a good model.

 

[foxint]

Hi Neil

Thanks again for the reply….

I think you lost me – sorry….

Since I am a DIYer (with limited experience), plus I have speakers that have Neutrik SpeakON connectors…essentially 2 connectors (one for the HF and one for the LF). There is no space inside the speaker.

While we all need the stuff to look good for our better halves…. but more than happy having a few nice looking boxes as I cannot fit anything in the speakers. Plus, this allows me the ability to upgrade each step in the system.

Perhaps I am not understanding the situation….

1 Solution

Source (box)…. into
DSP box into
Left Channel Digital Amplifier (box) with 2 (+/-) cable to the speaker (HF & LF)
Right Channel Digital Amplifier (box) with 2 (+/-) cable to the speaker (HF & LF)

2. Solution
PC with source and DSP into
Left Channel Digital Amplifier (box) with 2 (+/-) cable to the speaker (HF & LF)
Right Channel Digital Amplifier (box) with 2 (+/-) cable to the speaker (HF & LF)


Are you telling me a single STA326 chip does everything (DSP amplification DAC) …...??

Source (SPDIF out) into
STA326 into 4 outs (2 to Left Speaker and 2 to Right Speaker) ….

OK so if such a device exists (please let me it does….) I just connect my optical out (yes I love optical out) to the STA326 and the other side to the speakers (HF&LF Left and HF&LF Right).

Nirvana!!!????

 

[Neil Davis]

Not quite Nirvana. The STA326 and the other class D amp chips that have embedded DSP don't have an optical input, but it only takes a small amount of circuitry to do that. All of those chips have I2S input, which is what an SPDIF receiver chip will provide. So just add an optical receiver and an SPDIF chip and lots of software for the microprocessor, and yes, you will have a very compact amplifier with DSP and optical input.

You are correct in describing different connection options, but there are actually 4 different scenarios described in this thread.

The first--call it #0, is putting the DSP and amplifiers inside the speaker. That is my preference, but it requires a lot of software design tools to "get it right", which is why I wrote the Active Speaker Designer (ASD). I've described that software in other posts on this forum. And yes, you need to plan ahead for the mechanical issues of putting the electronics inside the speaker and providing heat sinking and power and provisions to update the DSP. Slide 15 of that briefing shows an example of a compact DSP amp that can be mounted in a speaker.

The second scenario is what you call #1. That's using an amplifier with embedded DSP for the crossover. I've made a number of those--there is a picture of one on slide 16 of that briefing. I've got a much nicer one with SpeakON connectors for all of the outputs--but I never bothered to take a picture. The STA326 amps *could* be used this way, because there are enough internal biquads to implement the crossover. However, none of the commercial STA326 amps are used this way--they actually don't use all of those nice DSP resources. They use the volume and digital filters for tone controls and EQ, but there are still a lot of biquads that could be used for the crossover.

And then there is the scenario where the DSP is a separate box--that is what you call #2. However, usually this approach converts the signal to analog, since there aren't any established ways to route multiple channels of digital audio between boxes. The routing can be done digitally, but the solution will be proprietary and not supported by other hardware. So this approach isn't too attractive if you are trying to maintain a fully digital signal path.

And finally, if your source is a PC, you can do the crossovers in the source and output HF, LF and other frequency bands through a soundcard in the PC (that's what the Ultimate Equalizer does). But again, this approach uses analog outputs from the soundcard to drive the amps, which is not what this thread is about.

There are some other configurations possible with networked audio, but the one that probably has the most promise is the active speaker that can extract the audio and do all of the DSP and amplification inside the speaker. There are a lot of variations on that approach, but amps like the STA326, with embedded DSP, can play a role in those designs. What's interesting about the networked audio is that it usually takes a potent processor and an operating system to run the TCPIP stack, so you can also do the digital filtering in that processor. That's the approach Charlie Laub has been describing.

 

[foxint]

Hi Neil

You are indeed a very knowledgeable man. Thank you. It has been confusing, but very interesting.

OK… I think I have understood some of what you have said…. Looking at the available hardware, I think the BEST (for me) is to get a TOTAL software solution that can output HF&LF Left out of (say) 1 USB and HF&LF Right out of another USD and conned each to a stereo Digital Amp.

So my question is…. To remain in the digital realm – is there a software solution???

Then I can take the 2 x USB outputs and plug them into two Stereo Digital Amps….

How about that – simple and I reduce the amount of boxes and no soldering…simple..????

Am I asking the impossible?

 

[Kjeldsen]

try read this.

Windows PC as a FIR Audio Processor

You can outout both analogue, SPDIF and I2S, and let the PC do the crossovers. You do not need to use FIR crossovers. There are IIR filters available for VST as well.

Or you can buy a couple of these

Hifimediy DDX320v2.3 - 2.1 Digital Amplifier