If the speakers are not enclosed at all, even a shoebox stuffed with crumpled newspaper would do more for volume than using a bridged amp.

 

Hello,

The following pages shows some enclosure design tips for the speaker:
https://sound-au.com/articles/enclosures.htm

Bertus

 

The datasheet for the 4" speaker shows a 100Hz cutoff in a sealed 5"x 5" x 5" enclosure or a 48Hz cutoff in a huge, vented enclosure. This speaker is only a little larger than the small 3" speaker in a cheap clock radio so it is not loud.

The Ni-Cad or Ni-MH 7.2V batteries are 9V when fully charged and drop to 6V or less when used then the idle current is not well controlled.

In Google I saw assembled amplifier boards using the PAM8610 class-D stereo IC selling for $1.98US plus $3.00US shipping.
With a 12.6V supply, the low distortion output is 5.7W per channel intro 8 ohms and the idle current is only 26mA. A very small heatsink might be needed.

 

TS needs to understand and appreciate the importance of the baffle board.

The first attempt is to try and create an infinite baffle board. This is to ensure that the back wave never meets the front wave. This is not a practical solution and compromises are used, for example, a closed speaker enclosure with acoustic absorbing material on the inside.

Furthermore, the baffle board is an extension of the speaker cone. Some of the energy from the transducer also radiates from the baffle board thus improving output at low frequencies

 

Hello,

The TS might also have a look at the books of Douglas Self:
https://archive.org/details/audio-power-amplifier-design-handbook-4th-ed./mode/2up
https://archive.org/details/self-on-audio-2nd-ed./mode/2up

Those will give a lot of details on how to design an audio amplifier.

Bertus

 

Also TS should be aware that there are millions (or billions) of devices on the planet with audio amplifiers that do not use bridged outputs.

 

Hello,

The TS might also have a look at the books of Douglas Self:
https://archive.org/details/audio-power-amplifier-design-handbook-4th-ed./mode/2up
https://archive.org/details/self-on-audio-2nd-ed./mode/2up

Those will give a lot of details on how to design an audio amplifier.

Bertus

It's almost two months since I suggest the very same thing:
https://forum.allaboutcircuits.com/threads/fine-tuning-a-transistor-amplifier.188868/#post-1759035 post #7
and has his circuit improved since then?

 

And another irritation.

TS is trying to measure distortion with an oscilloscope. You cannot measure distortion without expensive instruments.
I measure distortion by listening to the speaker output.

And I can go on and on...

 

And another irritation.

TS is trying to measure distortion with an oscilloscope. You cannot measure distortion without expensive instruments.
I measure distortion by listening to the speaker output.

And I can go on and on...

If you can see distortion on an oscilloscope then there's far too much of it! I would suggest that the distortion needs to improve by at least three orders of magnitude before it is worth investing in an Audio Precision analyser!

 

Hello,

Also what he will see on his oscilloscope will be dependend on the quality of the input signal.
Bad in is bad out.

Bertus

 

Hello,

Also what he will see on his oscilloscope will be dependend on the quality of the input signal.
Bad in is bad out.

Bertus

Good in is also bad out for his amplifier.

 

Also TS should be aware that there are millions (or billions) of devices on the planet with audio amplifiers that do not use bridged outputs.

Bridged outputs create 3.5 times more power than a single ordinary amplifier when using his fairly low voltage (7.2V) rechargeable battery. Almost all ordinary car amplifiers are bridged for that reason. His single amplifier has a maximum output (almost clipping) of 6Vp-p when powered from 7.2V which is only 0.56W into 8 ohms per channel. When bridged and adjusted for symmetrical clipping on both sides, the output is about 2W. He was also thinking about using two batteries for 14.4V plus bridging to almost get "car-radio" power, except car radios use 4 ohm speakers and his amplifier will need re-design to drive 4 ohm speakers with a 14.4V supply. Also, his little batteries will die sooner.

About 50 and 60 years ago I designed and made audio amplifiers with transistors.
About 40 years ago I made a portable sound system for the beach that is similar to the one in this thread (a mono 4" woofer plus smaller satellite stereo speakers, and one 7.2V rechargeable battery) using stereo amplifier ICs wired for bridged. It sounded much better than all the ghetto blasters there.

 

My DIY portable bass guitar amplifier is rated at 150W x2 and runs off a 12V battery. The car audio amp has 2 channels, intended for stereo operation but it can be bridged for single channel operation. I am driving a 12" 250W speaker in bridged mode. Internally, the amp creates a ±60V power supply from 12VDC input.

I do not object if someone wants to play around with Class A, AB, B, or D audio amplifiers to gain knowledge and experience.
If your goal is to build the best, low power, compact, battery operated audio amplifier then Class D is the obvious solution.
Unfortunately, TS's method is to try random method and components without knowing the proper reasons why, while ignoring advice from experienced electronics designers.

 

The TS is under the impression that there is a magic value of VAS load resistor that will turn his rubbish amplifier into a fabulous amplifier, if only he could find that magic value.. . . .

 

Mike was properly using a simulator to make fairly good circuits but his real parts need to be selected and adjusted so that they have perfect matching like the simulation or parts on an IC have.

Many years ago when little amplifiers like this one were made with separate transistors, the parts were matched and trimpots were used for adjustments.

The PAM8006A replaces the PAM8610 that I mentioned before. It produces 6W per channel into 8 ohms with a 12V supply at very low distortion or 8.5W per channel at fairly low distortion.
I wonder if cheap Chinese assembled modules use good ones or factory rejects?