Your circuit is missing the very important 10 ohms in series with 0.05uf (47nF) at the output to ground (they are shown on every circuit in the datasheet) that prevents oscillation at a high frequency.
The datasheet for the American LM386 shows typical distortion of only 0.2% when its gain is low but with your high gain it might produce 2% distortion.
The LM386 is a cheap low power IC made for cheap clock radios. There are a few other cheap low power amplifier ICs with the same low spec's, the TDA7052A is not available in a through-holes package anymore.
Why not do what is shown on the designer's datasheet? The RC is connected with very short wires DIRECTLY to the output pin of the amplifier.Thanks for your reply. I will try your suggestion to use a 10 ohm and 47nF though I don't know for sure if I should place them before the 470uF or replace it with them.
The TDA7052A amplifier is completely different to an LM386. It has a bridged two-amplifiers output so its maximum supply is 6V when it drives an 8 ohm speaker then its output power is about 0.9W at clipping and it will be hot. Its distortion is a little higher than an LM386 at about 0.3% to 1%.I've looked on eBay and found many TDA7052A available in DIP 8/same configuration as the Lm386 I'm using, so if it can be placed directly in place of the LM386, I could order some and give it a try.
Why not do what is shown on the designer's datasheet? The RC is connected with very short wires DIRECTLY to the output pin of the amplifier.
There are a few low noise opamps available. A very good one is the OPA134 that can work from a single polarity supply from 5V to 36V.
A speaker works from AC. The 470uF capacitor passes AC and blocks the DC (half the supply voltage) at the output of the amplifier from going into the speaker and offsetting its cone.I meant that I don't know if I'd still keep in place that 470uF capacitor and just add the 10 ohm and 47nF or place them (10 ohm & 47nF) and remove the 470uF
With a single polarity supply, the output of the preamp opamp is at half the supply voltage but the input voltage of the LM386 must be at 0V because it has internal biasing. So use a coupling capacitor between them to pass the AC but block the DC.I don't know what would be the right pinout wiring between OPA134 and LM386, so unless somebody would lend a hand I'm stuck at this point.
Correct.1) remove that 10uF capacitor between LM386's pin 1 and 8 to set it at its lowest gain setting (20)
Correct.2) place a 10 ohm resistor and a 47nF capacitor connected directly to LM386's pin 5 as shown in texas instruments' datasheet
Correct.3) use OPA134 as preamp and put it ahead of LM386
The OPA134 opamp and LM386 power amp operate at high frequencies. A breadboard with all its strips of contacts and wires all over the place with capacitance between them will probably cause oscillation. Also, the wires will probably pickup hum and other interference. Instead of a breadboard use a pcb or a compact stripboard soldered circuit.However, even if above statements may have reached correctly my mind, switching to action on the breadboard and later on the soldering station is another thing.
The 50k pot is the volume control. Offset trim is needed on a DC amplifier but your preamp is an AC amplifier so offset trim is not needed.For example, would I need/would it be better to leave that 50K trimmer in its place (connected to LM386's pin 3 and then grounding one end and connecting to that capacitor the other one) or would I have to put it between OPA134's pin 1 & 8 (offset trim)?
The preamp opamp needs an input bias voltage at half the supply voltage. Add another coupling capacitor at the of the output of the volume control that feeds the biased input of the preamp opamp. The preamp opamp needs two feedback resistors to set its AC gain.Also, how would I connect OPA134 and LM386 and hence how would the circuit be upgraded? Should I have to put any capacitors to set OPA134 values or would I just have to place it ahead of phototransistor's signal?
Sorry, but this simple project is far too complicated for your inexperience.I know that last thing you'd want to read is me asking for an update circuit drawing or hand-drawing since it may look like spoonfeeding, but I am otherwise far from catching up how to apply what you all kindly suggested.
That is how it is done.It isn't complicated.
The value of the coupling capacitor is calculated with a simple formula involving the source impedance (the output of the photo-transistor), load resistance (the two Why does the software on this site do this to my text?I've got one more doubt: which value should be the capacitor you draw at OPA134's pin 3 (signal in) between the two 100K resistors
Use the original photo-transistor circuit.would it be ok to connect phototransistor's collector/gather at capacitor's IN and phototransistor's emitter at GND or should I apply a 10K resistor to phototransistor's emitter?
If you told us what the expected frequencies are it would help us advise on the values. As it is, the whole of the audio spectum would be handled quite well but the use of coupling capacitors anywhere in a circuit introduces a frequency dependent element because their reactance (like resistance but to signals rather than DC) increases as the frequency drops. In essence, they are less effective at passing low frequencies than high ones and this applies to the input coupling capacitor, the loudspeaker coupling capacitor and the one in the pre-amp feedback path. Don't lose sleep over it though, the change over frequency is gradual and in an amplifier of this simplicity, I wouldn't expect you to be striving for sound excellence.
What is your photo-transistor actually picking up?
Brian.
It smells like a circuit for snooping (spying) on somebody.That photo-transistor is picking up a laser beam reflected off a surface.
It smells like a circuit for snooping (spying) on somebody.
Voices in a room vibrate the glass on a picture hanging on the wall. The laser beam shines into the room through the window and reflects off the picture glass with the vibrations modulating it.
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