Hello AllAboutCircuits Forum,

This is my first post! I'm building a portable audio amplifier. I'm hoping for stereo 2 x (5W - 7W) power into 8 Ohms, using lip0 3.7v ~1000mAH battery. I'd like the charger to be integrated on the same board if possible. (kind of like this https://www.adafruit.com/product/2130 plus this https://www.adafruit.com/product/2465) I've tried the PAM8403, but it's only does 3W max. The Diodes PAM8610 has almost too much power and requires 12v. If I could find something close to the power of the 8610, but that can use 3.7v batteries, I'd be super grateful!

Thanks!

 

hi,
Look at the TDA series.
E

 

How about the TDA7266. , 7W+7W, 3-18V supply.


http://www.st.com/en/audio-ics/tda7266.html

 

Hello,

You will have a hard time finding a chip that can give the 5 Watts at 3.7 Volts.
When you would use a double voltage of 7.4 Volts, the search would already be much easier.

Bertus

 

Thanks for the tips! My project is really tiny so I'm hoping for a class-D amp microchip around the size of the Diodes PAM8403. I looked at a couple projects on youtube using the TDA and I will keep it in mind.

 

Hello,

You will have a hard time finding a chip that can give the 5 Watts at 3.7 Volts.
When you would use a double voltage of 7.4 Volts, the search would already be much easier.

Bertus

You are right! I am having a hard time! I hacked something together using this Oontz bluetooth speaker that is 2 x 5W and runs off a 3.7v lipo(18650 I think) but I couldn't identify the chips on the board. The main chip says JL AC1535cg690x b1

I'm definitely open to 7.4v. I just need to keep the whole thing really small. Any chip suggestions if I do 7.4v? and charger?

 

Do the math.

If the output swings from 0 to 4V peak-to-peak, that is 2V amplitude, which is about 1.4V RMS.
Power into 8Ω speaker = 1.4 x 1.4 / 8 ≅ 250mW.

 

A bridged amp can can provide 4 times that or 1W.

You need 9V min to get 5W RMS into 8 Ohms in a bridged amp.

Bob

 

Thanks for all the input! Sorry if I am asking for the impossible. The speakers in the Oontz product I referenced are 4 Ohms. I may be able to get speakers that are 4 Ohms for my project too. What is the best amp chip that will get me 5W per channel stereo into 4 Ohms?

 

How about the TPA3144.
It's Class D so has high efficiency to maximize battery life.
It should give over 5W into 4 ohms with a 7.2V battery.

 

Thank you Crutschow!

That board looks good for 7.2v. I'm going to order a sample. I'm also looking for a evaluation board or an existing project that incorporates it so I can test it for my application without having to build it myself first.

 

The TPA3144 amplifier produces 6 Whats into 4 ohms when its supply is 7V and its clipping distortion is awful at 10%!
You never want to listen to 10% of clipping distortion (maybe acid rock?) but the datasheet does not say how much power when the output is
below clipping which might be only 3 Watts. When the 2-cells lithium battery is fully charged at 8.4V then the power might be 4 Watts at low distortion.

A "What" is a very distorted Watt so that the power number is higher. Many amplifiers are falsely rated in Whats instead of Watts.

 

The TPA3144 amplifier produces 6 Whats into 4 ohms when its supply is 7V and its clipping distortion is awful at 10%!
You never want to listen to 10% of clipping distortion (maybe acid rock?) but the datasheet does not say how much power when the output is
below clipping which might be only 3 Watts. When the 2-cells lithium battery is fully charged at 8.4V then the power might be 4 Watts at low distortion.

A "What" is a very distorted Watt so that the power number is higher. Many amplifiers are falsely rated in Whats instead of Watts.

That's funny!!! I remember going to buy stereo amplifiers as a kid and some of them were super cheap with enormous power ratings...they were definitely using "Whats" ha ha!

Do you have any other suggestions for a suitable chip? I'm powering some exciters that are 8 Ohms. I haven't found suitable replacements that are 4 Ohms. This question will probably show my ignorance, but would it be possible to modify a speaker to make it 4 Ohms instead of 8?

 

If you connect two 8Ω loudspeakers in parallel that will effectively give you 4Ω impedance.
Just make sure that the loudspeakers are in-phase otherwise you will get wave cancellation.

 

I think the TPA3144 will likely give as much power as any other chip into a speaker for a given power supply voltage.

 

If you connect two 8Ω loudspeakers in parallel that will effectively give you 4Ω impedance.
Just make sure that the loudspeakers are in-phase otherwise you will get wave cancellation.

Thanks! Unfortunately, I can only use 2 speakers and I need to be in stereo so I don't think I can run them in parallel.

 

Thanks! Unfortunately, I can only use 2 speakers and I need to be in stereo so I don't think I can run them in parallel.

You could use an audio transformer but it would be simpler to get a 4Ω speaker.

 

So you either need to find 4Ω speakers, or operate from a higher voltage supply (>9V) if you want 5W of power.

 

Hello AllAboutCircuits Forum,

This is my first post! I'm building a portable audio amplifier. I'm hoping for stereo 2 x (5W - 7W) power into 8 Ohms, using lip0 3.7v ~1000mAH battery. I'd like the charger to be integrated on the same board if possible. (kind of like this https://www.adafruit.com/product/2130 plus this https://www.adafruit.com/product/2465) I've tried the PAM8403, but it's only does 3W max. The Diodes PAM8610 has almost too much power and requires 12v. If I could find something close to the power of the 8610, but that can use 3.7v batteries, I'd be super grateful!

Thanks!

With the voltage headroom you mention, a BTL amp chip might just about do it. You should also take a look in the general direction of class-D.

With only 3.7V to play with, you should try to get 4R speakers - or use a step up transformer.

The TDA7052 works well down to Vcc=5V and 4R speaker, but IIRC: its only 1W - there may be something bigger in that chip family.

 

I had a car where the speakers were 2 ohms for double the current and power of 4 ohm speakers.

Most or all the amplifier ICs we have been talking about are BTL and class-D but the supply of only 7.2V is too low for 5W into 4 ohms without severe clipping distortion.