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Power output to a speaker depends on the applied voltage, speaker impedance, and the capability of the supply to provide the appropriate amount of current.How would i go about changing this basic amplifier circuit to to have 10 times as much output (using another speaker).
How much of a change would it take to have 10 Watt of output?
Thanks for any help.
Make note of the current diagram. The BC547C is currently biased at 1.3V . If you increase the voltage into this circuit, you will need to adjust the left-most 18K and 150K resistors to maintain that bias.
You may also need to swap out the transistors for more capable parts... and I'm very curious, why do you want to convert this incredibly low power piezo based amplifier into a 10W analogue amplifier?
Just so you know, there are various classes of amplifiers.
Class-A - This is a linear amplifier that is closest to the current design. The transistors operate in the linear region and as such can get quite hot when dealing with higher powers.
Class-B - This is an improvement, in that it splits the work into two halves... instead of A running halfway between on/off all the time, it uses two transistors that rest pretty much off... when the signal is + one transistor turns on, and when the signal is - the other turns on. More efficient, but still in the linear operational range.
Class-AB - This is simply an improvement on the Class B, some wiring tricks to eliminate the need for a transformer. Still better, and still linear.
Class-D - This is a digital amplifier... in that the transistors are all the way on or all the way off. It uses PWM at a very high frequency, so if you want half a positive signal, the duty cycle will be 50%. In this way, the transistors dissipate much less heat by avoiding operating in the linear region. This design is much harder to build though.
These to start...
You may have better luck keeping the power down unless you plan to pop various transistors and other parts as you work your way through and troubleshoot things. You can buy very inexpensive Class-D amplifiers, but take a look at those classes I mentioned and you will find example schematics for all of them.
The same formula applies for increasing power output though... You pick a speaker, and to increase power, you increase the voltage you send to it. (The power supply MUST be able to provide enough current)
As an example... 10W from an 8Ω load would require 9V . (Which would draw a little over an Amp)
V = IR (Voltage = Current x Resistance)
P = IV (Power = Current x Voltage)
P = V^2 /R (Algebra turns the above two into... Power = Voltage Squared / Resistance)
V = SqRt( PR ) = 9V
So.. the design you have is capable of deliver over 10W to a speaker, but this particular amplifier is unsuitable to drive a normal speaker.
In order for a class A amplifier to driver 10W into an 8Ω speaker, you would need to change the collector resistor to about 8Ω, it would need a 36V power supply, and it would it would waste 80W when idling!
So, no, you cannot reasonably modify your circuit to be a 10W speaker driving amplifier.
Look up designs for audio power amplifiers. The latest and most efficient ones will be class D, and all of the others will be class AB. Both of these are much more complicated than the circuit you have posted.
Bob
So, no, you cannot reasonably modify your circuit to be a 10W speaker driving amplifier.
Look up designs for audio power amplifiers. The latest and most efficient ones will be class D, and all of the others will be class AB. Both of these are much more complicated than the circuit you have posted.
Bob
Thanks for the info about the different classes of amps (complete noob here). I dont necessary want it to push it to 10 watts output but will try to go to 2-4 watts and see how it goes.
The simplicity of the circuit is what i liked about it.
The simplicity of the circuit is what i liked about it.
I would strongly suggest you look into building your own class-A amplifier then instead of trying to modify this one. Your call, but I don't think this circuit is suitable to run a regular speaker.
Here is about the simplest amp that would reasonably drive an 8Ω speaker. It can deliver about 1/4 W before distorting noticeably. It has a gain of about 8 and is suitable for amplifying a signal from a headphone jack on a phone or MP3 player.
To increase the gain, put a 220uF capacitor across the emitter resistor of Q2.
To go much more power than this you would need to use a higher voltage, and replace the output transistors with darlingtons and make various other revisions.
Bob
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