Amplifier for a bluetooth speaker

Thread Starter

nikolopikolo

Joined Sep 17, 2020
7
Hi,

I've decided that I build my own portable bluetooth speaker from scratch. Now I want to make the amplifier and I'm wondering if I should use op amps for it or build the circuit out of only transistors. What would you recommend for me if I had decided to make it a 40 to 60W amplifier or is that way too much for such a speaker
 
Last edited:

BobTPH

Joined Jun 5, 2013
2,538
It is a lot more power than you need if it is used in an average indoor room. If used outdoors, or in a concert hall, it might not be enough.

Bob
 

Audioguru again

Joined Oct 21, 2019
1,908
Most amplifier modules are stereo (2 channels) and the power supply voltage and speaker impedance determine the maximum output power. Some modules already have a Bluetooth receiver in them.

With a 24V supply, a TPA3116D2 amp IC produces 33W per channel into 8 ohms at low distortion or 55W into 4 ohms.
It produces 40W into 4 ohms with a 21V supply.
A high quality Parts Express Dayton 5" woofer can survive 40W and produce bass frequencies down to about 50Hz. Its enclosure will be too big to carry far.
The battery can be five 18650 lithium cells to make 21V at a full charge down to 16V when they are almost dead.
 
Last edited:

Thread Starter

nikolopikolo

Joined Sep 17, 2020
7
Alright, now I would like to know which IC would you recommend me to use for my amp design or if maybe you got some circuits I'd be more than happy to recieve them. I've decided I want to do the project on my own PCB, so no premade modules are of any use to me. The idea here is that It's as small as possible in size and can still deliver power in range somewhere between 20W to 50W. I've been looking into some TDA series ICs, but I could really use a professional opinion.

Appreciate your help, Nik
 

Audioguru again

Joined Oct 21, 2019
1,908
Do you want an older IC (TDA7294 mono amplifier) that uses class-AB and needs a fairly high supply voltage? A class-AB amplifier is analog and produces almost as much power making heat as its output power.
Or do you want a modern class-D switching amplifier (TPA3116D2 stereo amplifier) for low heat that has bridged outputs so it can be powered with a low supply voltage?
 

MisterBill2

Joined Jan 23, 2018
6,997
A 20 to 50 watt amplifier is going to take a serious amount of battery power no matter what, even at 100% efficiency, which is not reasonable. Is this portable box intended to supply music for a longer time period, or only an hour? There are some "fairly good" switchmode amplifiers available, along with detailed application notes that show circuits and layouts that avoid problems.
 

BobTPH

Joined Jun 5, 2013
2,538
The idea here is that It's as small as possible in size and can still deliver power in range somewhere between 20W to 50W.
That requirement alone eliminates class AB amps. The heat sinks alone would be larger than a class D amp.

As an added bonus you get nearly twice the battery life.

I hope you are capable of soldering SMT chips.

Bob
 

Audioguru again

Joined Oct 21, 2019
1,908
Cheap assembled Chinese modern class-D amplifiers are available with American numbers on the ICs (maybe real ones?) and maybe with suitable little heatsinks.
 

Audioguru again

Joined Oct 21, 2019
1,908
The TPA3116 amplifier IC has 32 surface-mount pins and is half the size of your smallest fingernail. How can anybody solder it to its very complicated pcb (the pcb details are on the datasheet)?
The Bluetooth IC is also surface-mount and is tiny with many pins.

Will your portable speaker be stereo but in one enclosure?
 

MisterBill2

Joined Jan 23, 2018
6,997
Soldering is not the problem, but it does require a very fine tip iron, a steady hand, and a serious magnifier. And a whole lot of patience. You do need to get the board with solder resist coating though.
 

Thread Starter

nikolopikolo

Joined Sep 17, 2020
7
Okay, so I'll be using the TPA3116D2 IC to build a class-D amp. It will be a stereo portable speaker in one enclosure. Battery life is also important to me ofcourse sience I'm planning on adding other functions to the speaker like reactive LEDs. It should last for 6 hours at a little more than half volume that is the ideal speaker for me. As for soldering the chip goes, I've got a solid solder iron a pretty good magnifier I'd say and I can get my hands steady. Now, is my power requerments over the top with this kind of build or can it be pulled off.

Nik
 

Audioguru again

Joined Oct 21, 2019
1,908
Two stereo speakers in one enclosure is silly since the speakers are so close together that everybody hears mono.
But all other sound systems are stereo or have surround sound so mono amplifier ICs are rare to find.

You are probably not playing continuous full power tones that will drain a battery quickly.
The ratio of from maximum power to average power for music and speech is about 10 times and you want almost half volume that is also reduced 5 times (our hearing's sensitivity is logarithmic) then your average output power and battery current will be fairly low. But when you turn up the volume then the battery life will be one-fifth.

All other portable sound systems on these forums use purchased amplifiers or Bluetooth amplifiers.
 

MisterBill2

Joined Jan 23, 2018
6,997
I have found that stereo from adjacent speakers pointed in opposite directions in a medium to small size room is quite satisfactory, AG, and so I would not knock it. Certainly it does not match the ping-pong effect that some music provides, but that stuff gets boring after a few minutes.
 

Audioguru again

Joined Oct 21, 2019
1,908
I have found that stereo from adjacent speakers pointed in opposite directions in a medium to small size room is quite satisfactory, AG, and so I would not knock it. Certainly it does not match the ping-pong effect that some music provides, but that stuff gets boring after a few minutes.
Opposite directions?
Tweeters are directional and should be facing the listeners for all frequencies to be heard.
I do not think this portable amplified Bluetooth speaker will be playing a muffled AM radio talk show.

Stereo music produces an ambience, rarely the ping pong effect. In comparison, mono sounds dull.
 

MisterBill2

Joined Jan 23, 2018
6,997
Speakers mounted on adjacent sides, at right angles to each other. Fairly simple to do and while it certainly does not match the $2500 system of some folks, the sound is just what some can appreciate.
Nobody else is talking about AM talk radio, so why throw stones???
 

Audioguru again

Joined Oct 21, 2019
1,908
Speakers mounted on adjacent sides, at right angles to each other. Fairly simple to do and while it certainly does not match the $2500 system of some folks, the sound is just what some can appreciate.
Nobody else is talking about AM talk radio, so why throw stones???
Thank-you for correcting your speaker mounting wording.
Speakers at right angles will probably be fine but not speakers mounted "in opposite directions".
 
Top