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Old 26th September 2012, 02:15 PM   #11
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actually my speaker is 4 ohms o.o
and my ears are super sensitive to distortion so I always make sure to keep the volume on my computer set just right so it doesn't have any distortion or it really messes up the sound quality. and i'm not exactly for sure know what resistor i have... it could be anything because since I took it off of a old TV motherboard i was trying a bunch of resistors until i found one that worked good enough so it could be anything..

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Old 26th September 2012, 03:03 PM   #12
Mooly is offline Mooly  United Kingdom
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You would have to measure the DC resistance of the voice coil to get a true resistance value. 4Ω, 8Ω etc are nominal "impedance" values. The impedance or "resistance" of a speaker varies wildly with frequency.
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Old 26th September 2012, 03:04 PM   #13
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sorry it won't let me edit my post but I wanted to add that i think my batteries may be finally dying so i might have to go buy some new ones soon... (a little more distortion than usual today)
also I would have to hugely change the resistor if i wanted to have more power... i would need to change it enough so my amp has almost no power flowing through it because the more power i need.. i need a transistor that's even more ohms than before.. if i wanted to upgrade to a 12 volt power supply i would basically need to change it to almost 300,000 or something like that because if i add one more double a battery it makes the voltage in my amplifier go shooting through the roof..
by the way I don't use anything close to a 0.1uF or a 1.0uF
I use a 2200uF capacitor for the input for much more bass.. enough bass to move a 175 watt subwoofer! that's my good DUAL subwoofer i bought from walmart and not the paper speaker in the pictures i showed earlier.. i should make a video showing my home made amplifier powering the big subwoofer : D

and sure.. at certain frequencies of bass it distorts more than other frequencies.. though there is almost no treble or high frequency distortion which i think is pretty good
by the way there is no static or background noise whatsoever in this amplifier i made.. and no buzzing sound when i touch the end of the input plug like the other amplifiers make.

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Old 26th September 2012, 03:48 PM   #14
lohk is online now lohk  Europe
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you should use the 2200uF cap for the output...
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Old 26th September 2012, 03:55 PM   #15
Mooly is offline Mooly  United Kingdom
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If you have around 3 volts (with new batteries) across the speaker and the speaker measures (say) 4ohm then the current flowing is I=V/R which is 0.75 amp. Lets say the capacity of a new alkaline cell is what, 2Ah, (it's in the right ballpark) so that gives a life of 2/0.75 which is around 2.5 hours.

The resistor sets the operating point. Ideally the resistor should be set to give around half the supply voltage across the speaker so that the signal can swing equally in each direction. Its value depends totally on the transistor characteristics... not good design... but to do it differently means you reading up a lot more on how transistors and basic circuits work.

You have a working design. Now you need to really understand how it actually works and why it behaves as it does
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Old 26th September 2012, 04:00 PM   #16
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by lohk View Post
you should use the 2200uF cap for the output...
That takes it to a much more complex design I agree the amp as it stands isn't practical but its a good starting point to learn.

Look at how the amp achieves its voltage gain and also achieves a good voltage swing across the speaker.
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Old 26th September 2012, 04:22 PM   #17
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omg I changed the resistor to a slightly smaller one and I changed my power supply to a 5 volt usb at only 700mA and now it's even more powerful than with the batteries and now my 12 inch subwoofer is getting what looks like.... at least 10-20 watts!! it's flexing like crazy now almost a fourth of an inch woofer movement! and there is less distortion than before! but the transistor gets a bit warm but it's not too warm since i changed the resistor to allow less DC to flow. it's about as warm as with the double a batteries but much more powerful
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Old 18th October 2012, 12:14 PM   #18
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Default I do love to play with such kind of circuits too

This produces a real fun.

regards,

Carlos
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Old 18th October 2012, 03:27 PM   #19
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I do love to play with such kind of circuits too
Please teach me how to connect the wire...
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