Electronics > Beginners
need a speaker a resistor?
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Irukandji:
Hi i tryed to calculate and draw (with paint) the circuit. Did i need a resistor on the place with the question symbol?
hamster_nz:
I am pretty sure that will work. Make the unknown resistor 325 ohm too and you should be fine. It might be quiet as only 8/333ths of the power will be used in the speaker (maybe 4mW, if I can do the numbers in my head) .

If you need a bit of help, I could most likely build one here from parts I have to hand. The values for the capacitors will also need to be known, as the also control the frequency.

PS.the wattage shown on the speaker has one too many zeros
Zero999:
Yes, a resistor is required, for the circuit to work properly.

The transistor's bases or emitters should also have diodes in series, to protect them against the reverse voltage generated, when the opposite transistor turns on, connecting the positive side of the capacitor to 0V.

I'd recommend using a higher impedance speaker, a transformer with the 8Ω speaker, or a piezo transducer, but it can work with an 8Ω speaker, with relatively poor efficiency.
hamster_nz:

--- Quote from: Irukandji on May 01, 2018, 08:33:42 am ---Hi i tryed to calculate and draw (with paint) the circuit. Did i need a resistor on the place with the question symbol?


--- End quote ---

Well, I used S8050 NPN Transistors, 330 Ohm and 20k Ohm resistors, 22uF caps, and a 20W speaker, but your design is sound (and makes sound too!)

Works as drawn.

https://youtu.be/TidlGBrLYxk

(sorry for suck a crappy video)
Zero999:
It will work as originally drawn, but it doesn't mean it's a good design. The collector resistor on the speaker side, should be a lower value, to increase the volume and more importantly, the transistors need protection diodes, as their reverse base-emitter voltage ratings are likely being exceeded, which is bad for reliability.
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