Hello, I have 3 different amplifier circuit below, 2 are bought (adafruit 2.5 amp)and(tda2030a solder yourself Ebay amps) and one is a basic circuit that I have followed from an electronics website. I will have pics attached below... but I have used these 3 different circuits on a .5w/ 8-ohm speaker and a 1w /8ohm. The 2 amps that I bought online both produce background noise and are not that loud, even the adafruit with gain control) But the most simple circuit that i built produces louder and more clear sound. Can someone explain this?
No, we don't need a picture of a hand. What exactly is the jack plugged into when it's making sounds? And what sort of 5V supply is it and how much current can it provide?
The output from an amp is limited by its output power limit, but is also determined by the input voltage level and the amplifier gain. The simple preamp circuit is high gain if driven from a low impedance source like a headphone socket, so will be louder on a small signal than the others which are probably expecting line level
(400mV rms)
Headphone outputs are low level voltage and low impedance, standard audio amps expect line level (high impedance, high voltage level).
The faults with that preamp circuit include:
Its gain and feedback depends utterly on the source impedance.
Its putting DC through the speaker which is bad
Its overloading the BC547 which is a very low current device.
Its bias point setting is rudimentary at best.
It cannot swing anything like the full supply range.
So in summary if you want a loud output you need enough gain, and you need to be able to produce a
high enough output swing and handle the power involved.
