Schema amplificator de mica putere

Cre' ca si alea de la mama lor se duc la peste 12V din cate tin eu minte. Retin ca le-am dat maxim 9V sa vad cum merg si in original mergeau la 6V.

Mergeau. Ca ala original a tot mers 8 ani... Dar am luat 3 la rand care au bubuit la 15v dupa cateva zile, asa ca nu m'am mai riscat.

Amplificator portabil mi'am facut eu, intentionez sa'l fac sa incapa intr'o cutie de chibrituri mare. :) Momentan e inca pe un PCB de test, pt ca n'am mai gasit cutie. :P Dar este complet, si functioneaza perfect.

Este stereo, si se alimenteaza la 4.9v stabilizati printr'un LM317 din 2 baterii Li-Ion de la telefoane. Am ales tocmai valoarea asta pt ca cele 2 baterii, chiar si cand sunt aproape descarcate, sa poata alimenta circuitul in conditii optime. LM317 are nevoie de 1.5v minim diferenta intre intrare si iesire, 3.2v x 2 = 6.4 - 1.5 = 4.9 deci circuitul inca se alimenteaza.

Amplificarea e facuta cu 2x TDA2822M in punte, cate unul pe canal, iar la iesire am 2 difuzoare chinezesti din alea mici si rotunde, de 2 inci, 1W/8 Ohm. Si ca sa faca mai multa galagie i'am pus un filtru trece sus la 200Hz pe intrare, astfel difuzoarele nu se mai chinuie sa redea basi pe care oricum nu ii pot scoate, iar bateriile tin mai mult. :)

Pt cine intereseaza, o sa postez maine un video pe Youtube cu jucaria.

Notice that there is just one capacitor across the battery instead of a cap between each rail and virtual ground as in the resistor divider supply. In the resistor divider circuit, two capacitors are absolutely necessary to the success of the circuit. Below, I will talk about the advantages of using two caps like this in an active virtual ground circuit, as well as the disadvantages. For now, assume that it's better to have just one before the active "rail splitter".

Capacitors on the Output of a Virtual Ground Driver

Above I said that when moving to an active rail splitter, you want to seriously consider putting the rail capacitors in front of the splitter. The purpose of putting caps across the resistive ground divider shown at the start of this article is because this passive splitter cannot deliver very much current, so we need the caps to do that. The resistors are only maintaining the DC level of virtual ground here. An ideal virtual ground circuit would have infinite current delivery, so there should be no advantage to putting caps on its ouptut. In fact, it can be detrimental.

An active virtual ground circuit has some "bandwidth": that is, it will be effective over some range of frequencies. If you put capacitors across its output, that lowers its bandwidth: as frequency goes up, the capacitors are "in charge" to a greater and greater extent. If the caps are large enough, the virtual ground circuit's bandwidth is completely swamped. It could end up being good for no more than maintaining the DC level of virtual ground.

Output caps can be a good thing if the rail splitter has a fairly low output current limit. That's the situation in the MINT amp, for example. The TLE2426 has an output current limit of between 20 to 40 mA, depending on operating conditions. When it goes into current limiting, its output goes to the negative rail, which would make for a massive shift in the virtual ground point, so we cannot allow this to happen. A heavy headphone load could indeed exceed 20 mA, so putting caps on the ouptut of the TLE2426 saves the design. Although the TLE2426 has no effect at audio frequency, it still has benefits compared to a resistive voltage divider. First, its output impedance is much lower, so the virtual ground shift described above doesn't happen. Second, it requires less operating current than the CMoy's resistive divider.

Another potential problem with big caps on the output of a virtual ground splitter has to do with stability. Some circuits will become very stable in this situation: no bandwidth and no gain, hence no oscillation. Most circuits aren't made to cope with capacitive loads, however. They become less stable when driving a capacitive load. Study the datasheets for the ICs you will be using. Unless they specifically tout the fact that they can drive large capacitive loads, beware of using them in virtual ground circuits. Don't forget to consider the system bypass caps, if they go from each rail to virtual ground: there are many chips out there that will become unstable with less than a nanofarad of capacitance on their output, and the bypass capacitors will count against this. Ultimately, you will have to build real circuits and test them before you know whether a given chip can cope with the capacitive load in your setup.

There's one more problem with putting caps on the output of the virtual ground circuit: it wastes capacitance. In a very real sense, two caps across the output of a virtual ground circuit are in series, so the total capacitance is cut in half. Also, you require one capacitor in front of the rail splitter, but two after it. This means putting the rail capacitance in front of the splitter is actually four times as efficient: you can have twice the effective capacitance in half the board area, or four times the capacitance in the same board area.