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Class D Switching Power Amplifiers and Power D/A conversion

Audio-noob looking for suggestions on class D builds
Audio-noob looking for suggestions on class D builds
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Old 9th August 2018, 03:28 PM   #1
DRP1 is offline DRP1
diyAudio Member
Join Date: Jul 2018
Default Audio-noob looking for suggestions on class D builds

I am looking at starting a couple of Bluetooth speaker builds, but am looking at making from scratch rather than buying an EV kit or board from china. I have experience in electronics but not necessarily analogue or specifically audio. I do have quite a lot of experience in microcontrollers, electronic design, pcb design and control systems. I should’ve paid more attention in analogue electronics at school. I just thought it would be a fun project to do.

So,as a bit of background, the basic premise is to build the following 2 designs:
  • The first build: Portable active speaker, needs to be reasonable quality – I’m aiming for size and (hopefully) performance of my current portable speaker (B&OA2), Bluetooth connection, battery powered for a reasonable amount of time, possibly passive radiator (TBD, but it seems to work well on a lot of small speakers I’ve seen).
I’m looking at TAS3118 (chip) or similar, RN52 BT Module (?),NE5532, batteries (?), charging circuit, small micro possibly if easier than self boot, but need to look more closely at the spec on the BT/ DAC module to see whether needed.

This seems like a waste of money seeing as even producing a pcb will cost much, much more that a whole amplifier board shipped from china, but I seethis as a starting point, before jumping in to the other project and a learning curve in gaining some experience.

I did start looking at TPA3251 (digital I2S input) which has its own DAC and is reasonably well configurable via TI tools, but I’m unable to identify a decent BT module yet that outputs I2S (and is I2S good enough?)
  • The second build: Larger Mains Active Powered speaker/ speakers(?) – Mains powered, high power, good quality, Bluetooth/ analogue/ digital/ other(?) inputs, unsure about box design currently but would like to make something quite stylish (Ilike the B&O A9 or the Beoplay 1), possible additions once the thing is up and running is to add graphical screen/ motion sensors and some other fancy things – I’m looking for suggestions here before I start buying and building a dev board. I don’t mind spending and would prefer top end regarding soundquality, build quality and interface and is a longer term project to be startedafter getting the first one done but thinking/ making notes about it now.
For this second build I was originally looking at TPA3255, with RN52 BT module (A2DP CODEC on board), NE5532 (I need to check the voltage levels), homemade PSU(?) ,possibly simple microcontroller (maybe Microchip PIC, but only because I have loads lying around and they are simple to use – although I expect most people have moved on to other micros nowadays).

So, my question are:

Does these designs look ok, any advice?

Is there a better way? Such as Digital O/P BT Module (A2DP?), and then convert DAC with eg ADAU1701 (allowing use of extensive features of sigma studio, mixer/ filters/etc. and safeloading (without pops) of filter variables on the fly) and then into preamplifier and on to TPA3255, maybe?

Is there a BT module that has out digital output that anyone can recommend? Also,is A2DP better than I2S for audio – I’m expecting yes, but haven’t yet found that answer myself.

Any projects that people can point me to that may be a good reference?

And speakers, yes, I’ve looked, but there’s way too many to narrow down. Suggestions more than welcome, before I dig deeper in this area.

Hi, by the way, and many thanks in advance for any advice or suggestions.

*Edited to hopefully add a bit of clarity to the post*

Last edited by DRP1; 9th August 2018 at 06:20 PM.
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Old 9th August 2018, 05:41 PM   #2
FauxFrench is offline FauxFrench  France
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Join Date: Dec 2017
Location: The mountains, calm and quiet.
Hej DRP1,

Your questions seem a bit ambiguous to me in the sense that you start telling you are an audio "noob", do not want to start with a kit or China board but aim at "making from scratch". Then, you start mentioning some good and rather powerful amplifier component that do not fit well with that it should end up with a portable speaker. You then dive into some details concerning communication protocols. You were at zero replies perhaps because your project could appear to lack some focus.
Sorry for being rather blunt.

First, could you indicate an economical budget for your project? What we recommend depends on the price level you see as realistic.

The B&O A2 is pretty small. The B&O A9 is rather big and not portable.
What size do you expect to end up with? The reason why I ask is a TPA3255 amplifier with a reasonable battery can for sure not enter a B&O A2 and hardly a B&O A9.

Finding a powerful and well playing class D amplifier is not so difficult but finding a reasonable sized battery to feed it is expensive and takes up space nevertheless with the capacity you may need.

Most class D amplifier chips are supplied in SOP or SSOP chip-housings for SMD mounting. That makes "making from scratch" very difficult. You also seem to realize that just making the PCB cost more that an assembled board from China. What do you actually mean with "making from scratch"?

The Bluetooth protocol and bus interface seem like details for a start.

What is your realistic sound ambition level? - "sounds good" or "can beat Sonos"?

What output power do you realistically need?

Could you eventually give us a bit more precise boarders for the project?

Last edited by FauxFrench; 9th August 2018 at 05:53 PM.
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Old 9th August 2018, 05:56 PM   #3
DRP1 is offline DRP1
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Join Date: Jul 2018
Hi Faux, Thanks for your response, no need to apologise. Maybe I was confusing the situation by running ahead a bit.

There are 2 builds I plan to do. they were numbered, but it seems the forum has replaced numbers for bullets (I pasted in from a word doc - old habit). Which adds slightly to the confusion.

The first being a smaller battery powered system as an intro into building a class D active speaker. Making from scratch - I will design the circuit using TPA/TASxxx and have the PCB made, assemble with SMD components, etc, design enclosure and make it myself - not sure how yet, but I did see some quite interesting videos on 3D printing ;-)

The second system is a mains powered, all singing system, putting into practice, hopefully, what I learn on the first build, but 2 very different active speakers. Sorry if this adds to the confusion.

Hope that gives a bit of clarification.
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Old 9th August 2018, 05:59 PM   #4
DRP1 is offline DRP1
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Join Date: Jul 2018
As for sound ambition level, for the first speaker if I can get near the A2 performance (I own one so can compare), then I will be happy.

As for the later build, I want that to be amazing :-)
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Old 9th August 2018, 08:02 PM   #5
FauxFrench is offline FauxFrench  France
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Join Date: Dec 2017
Location: The mountains, calm and quiet.
Fine, then I propose "good sound" for the first project. Many, probably young people, have big dreams about more than 2x100W, portable and evidently running from batteries. Our experienced forum members with particular experience on portable speakers (often Dutch) have patiently explained that the batteries are typically the limiting factor for portable speakers.

When reality has been accepted, the portable speaker specifications often end up looking something like:
Output power in the range 8-30W per channel
Amplifier modules based on TPA3116 or TPA3118, often in PBTL configuration
Batteries based on 16650/18650 lithium elements. 12-24V, 5Ah-15Ah
Speaker driver(s) in the range 3 Inch to 6.5 Inch
Speaker cabinet according to your skills.
Bluetooth (type?)

Such specifications will cost you in the order of 150-200 EUR (1200-1500 DKR) per speaker. The batteries and the speaker cabinet being the most expensive. This is a realistic project.

You find several threads on this forum discussing such portable speakers.

The TPA3116/TPA3118 amplifiers are particularly suited for portable speakers. Up to 50W per channel (IF, the battery can supply the current!), good efficiency (little heating inside the speaker cabinet), generous supply voltage range, very low price for China modules, good sound (but not the real top) and small size.
A TPA3255 amplifier has better sound but is far more complex in design and finding a battery that can supply all that power is difficult and very expensive.

Though it sounds uncomplicated, the battery (batteries) is one of the most critical components. There is quite a difference in the voltage from a battery when it charges, when it is fully charged and when it is almost ready for re-charge. At no time must the maximum supply voltage of the amplifier be exceeded and the output power with a used battery should still be reasonable (the battery voltage drops slowly as it is being discharged through use).
The battery is not just a trivial issue, you will learn.

Look around for similar project on this forum and wait for some of the really skilled forum members to give you advice. I guess they will soon show interest if you are just realistic about your aims.

Good luck with the project, FF

Last edited by FauxFrench; 9th August 2018 at 08:16 PM.
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Old 10th August 2018, 10:33 AM   #6
DRP1 is offline DRP1
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Join Date: Jul 2018
Thanks for the really good advice Faux. I hadnt considered the batteries beung such a limiting factor. I'll have a dig around the forum.

Its a paper exercise at the minute, so this practical advice is very useful to stop me wasting money early on.
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Old 10th August 2018, 10:56 AM   #7
DRP1 is offline DRP1
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Join Date: Jul 2018
A Designer's Guide to Lithium Ion (Li-ion) Battery Charging | DigiKey

Just looking around the tech and some charging circuit solutions. Some good advice in the above link.
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