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I'm a newbie in the world of electronics, and I decided to build a 3watt amplifier.

I searched arround the web and I found the following schematic for a 1w amplifier:

Note: put a 2k resistor in between the ground and the emmiter if you want to prevent little distorsion http://hackaweek.com/hacks/wp-content/uploads/2011/08/transistor-preamp-schematic.jpg

My question is: • What is the "next stage output" used for? • Can I put there more amplifiers if I want to gain more watts?

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  • \$\begingroup\$ Your link doesn't work \$\endgroup\$ – brhans Dec 28 '15 at 20:19
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    \$\begingroup\$ "Output to next stage" is, like it says, the output of this amplifier which should be fed to additional amplifier stages. The drawing says that this is a preamp - I'm sure it won't deliver anything near 1 watt. \$\endgroup\$ – Peter Bennett Dec 28 '15 at 20:41
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    \$\begingroup\$ This pre-amp will deliver you 9mW... You have a lot of learning to do before building a 1W amp. Believe it or not, 1W already is a bit challenging for a beginner in electronics due to the fact if you want it to have any quality of sound you need a multi stage design. That being said, there may be some IC chips that can do at least 1W, maybe some Class D chips that can do 3W. \$\endgroup\$ – MadHatter Dec 28 '15 at 20:54
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    \$\begingroup\$ @MadHatter there are definitely linear ICs available up to 30W or more. National made some on big heatsink packages that are amazing for what they are. But they're not really appropriate for beginners who want to learn. \$\endgroup\$ – Daniel Dec 28 '15 at 20:57
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    \$\begingroup\$ May I ask what your goal is spund3? Is that for quality sound? Because you want to learn? for audio? for RF? We may be able to point you to some material. \$\endgroup\$ – MadHatter Dec 28 '15 at 20:59
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This is a pre-amp for a microphone circuit. You can tell because they've tied the input to power through a resistor.

The next stage is there to feed the signal to either another amplifier stage or to feed it to a buffer stage. You'll need more reading to know which to use.

You can put more amplifiers to gain a larger signal. I hesitate to use the word "Power" because most people worry about the power as it is delivered to the load (a speaker). But be aware that your signal's Voltage gain is limited by the power rail, and that it's current gain is limited by how much current your supply can handle.

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"What is the "next stage output" used for?"
"Can I put there more amplifiers if I want to gain more watts?"

Audio input signals (e.g. from a microphone) are usually very low power signals that must be amplified before they are useful with other circuits. That's the purpose of a pre-amp circuit stage. The next stage is usually for greater signal amplification, however, if not design properly, noise often gets added to the signal--which would degrade the quality of the signal.

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This won't give you 1W, but an LM386N-4 has a rated output of 0.7W (700 mW) and could be used as a second stage amp. It has a volume control too.

enter image description here

You already have a 0.1 uF coupling capacitor so you don't need the one here between V\$_{IN}\$ and the pot.

By removing the 10 uF capacitor between pins 1 and 8, you can limit the gain to 20.

Note the sound quality won't be that great as the LM386 has a 10% THD. But it's a quick way to jack up the volume of your pre-amp with a minimum of parts. RadioShack has a LM386-1 but its rated output is only 300 mW.

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  • \$\begingroup\$ The LM386 datasheet ti.com/lit/ds/symlink/lm386.pdf shows a THD figure of 0.2 % under typical conditions - not exactly hi-fi, but fine through the average 1 W speaker. The 10 % figure is for maximum output, or more accurately 10 % THD is the level they chose to be the onset of clipping at which to calculate maximum power. \$\endgroup\$ – nekomatic Dec 31 '15 at 14:50
  • \$\begingroup\$ To hit the target of 1 W output into an 8 ohm speaker a better choice might be the LM380, although it may need some heatsinking - check the charts of power dissipation in the datasheet. \$\endgroup\$ – nekomatic Dec 31 '15 at 14:53

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