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Common emitter amplifier gives an amplified inverted output. So if I fed the inverted output to a speaker, would it sound fine ? If not, how do I get an amplified but non inverted output from a common emitter biased transistor ?

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In general, the absolute phase of audio signals doesn't matter.

But if it's a problem, just reverse the leads to the speaker!

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  • \$\begingroup\$ For stereo (or more) speakers, the relative phase matters, but that's not what the OP asked. \$\endgroup\$ – Spehro Pefhany Mar 30 '14 at 21:55
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You could get an inverted vocal signal by rotating a microphone 180 degrees - does this sound bad? Given all the reflections going on when you record live music AND all the reflections and acoustic reverb you get when you listen to music, it should be no surprise that doing a single electrical inversion has no audible effect whatsoever.

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No, it would NOT sound fine. A single BJT common-emitter amplifier only provides an active sink or source for one quadrant. You need a two-quadrant driver for a speaker; one that can sink and source current to the speaker. And inverting the signal isn't important if all you are doing is driving a speaker.

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    \$\begingroup\$ A single BJT CE amplifier is usually coupled to a speaker with either a large electrolytic capacitor or a transformer; either one removes the DC bias. Such setups are very common in low-power applications, and they sound just fine. \$\endgroup\$ – Dave Tweed Mar 30 '14 at 21:36
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    \$\begingroup\$ This is just plain wrong. Some very expensive high-end audiophile amplifiers are single-ended class A common-emitter (source, cathode) designs. For an example of DIY versions, see Pass DIY: passdiy.com/project/amplifiers/the-zen-amplifier \$\endgroup\$ – Alfred Centauri Mar 30 '14 at 21:42
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    \$\begingroup\$ You point is not a point at all. Whether the collector (drain, plate) load is active or not doesn't change the fact that your answer is incorrect. Single-ended class A amplifiers exist and produce remarkably good sound. \$\endgroup\$ – Alfred Centauri Mar 30 '14 at 21:50
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    \$\begingroup\$ I agree with the protests. This answer is wrong or misleading at best. If you want to put provisos in your answer for exactly what you mean I'll be interested to read again but I'm failing to see this would correct it much. \$\endgroup\$ – Andy aka Mar 30 '14 at 22:00
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    \$\begingroup\$ A transformer fed speaker in the collector isn't another active device and for years this was the de facto way of making a simple and reasonably low distortion class A amplifier. Admittedly using valves initially but similar circuits for transistors certainly we're also on offer and, I believe, still are. \$\endgroup\$ – Andy aka Mar 30 '14 at 22:13

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