Audio to speaker : Transistors

Thread Starter

Zeeus

Joined Apr 17, 2019
481
Hi...Made the first circuit yesterday : gain was about 300..If you look at 2nd image, channel 2 is the input and it says 20.88 mv but from the function generator it is 5mv..what's wrong?? probe is 1X...Read a post that says it's best to use 2 resistors in series at emitter then bypass one so will change

Also wanted to connect output to emitter followers (3rd image : I did not make the circuit )..like 4 emitter followers connected together so the leftmost follower has input impedance >60k (output impedance of first image is 6k)...Will this work? (I dunno : beginner here)...lol, I will not use 2n3904

Thanks Jony :) https://forum.allaboutcircuits.com/threads/coupling-class-a-amplifier-with-class-ab-amplifier.158961/#post-1388410
Reading push-pull, bootstrap and negative feedback today : hopefully slightly better design tomorrow : want to hear a voice from microphone to speaker with transistors

Also, think i've seen some audio transistor amplifiers and the input is inverted only once! why not twice to get the input back again?? it does not matter?

Thank you
 

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crutschow

Joined Mar 14, 2008
23,758
think i've seen some audio transistor amplifiers and the input is inverted only once! why not twice to get the input back again?? it does not matter?
Why do you think it would matter?
The only time phase matters in audio is between two or more speakers, such as stereo.
Then the phase to all the speakers must be the same.
 

Thread Starter

Zeeus

Joined Apr 17, 2019
481
Why do you think it would matter?
The only time phase matters in audio is between two or more speakers, such as stereo.
Then the phase to all the speakers must be the same.
oh..Thought maybe something like if one says "Hello" then something else would be heard from speaker
 

AnalogKid

Joined Aug 1, 2013
8,224
think I've seen some audio transistor amplifiers and the input is inverted only once! why not twice to get the input back again?? it does not matter?
Yes it does, in a subtle way.

Sound is the compression and rarefaction of air, but air does not behave the same for both. For something simple like the fan in the back of a PC or a window fan, the air flow out of the fan is directional. Yes, the air movement spreads out (diverges) the farther you are from the fan, but there is a noticeable drop-off in pressure and velocity as you move off the centerline. However, on the intake side of the fan the difference is much less. This is because you cannot shape vacuum (negative pressure) with a nozzle the way you can (positive) pressure.

A positive-going audio waveform is associated with the speaker cone moving outward, toward the listener. For a sharp transient like a cannon shot in the Overture to 1812, the initial "crack" is less distinct if the phasing is such that an increasing slope retracts the speaker cone. Of course, this assumes that everything else in the recording, mixing, pressing, and reproduction chains followed the standard.

ak
 

Audioguru

Joined Dec 20, 2007
11,251
A speaker is driven with a POWER amplifier that uses POWER transistors but the circuits you show cannot provide enough current to drive a low impedance speaker. The emitter-followers use a power supply voltage of only 1VDC so the little transistors will not even turn on.
 

Thread Starter

Zeeus

Joined Apr 17, 2019
481
A speaker is driven with a POWER amplifier that uses POWER transistors but the circuits you show cannot provide enough current to drive a low impedance speaker. The emitter-followers use a power supply voltage of only 1VDC so the little transistors will not even turn on.
It's meant to be 12v...The emitter followers like that will not work? the picture shows only two but four to use
 

Audioguru

Joined Dec 20, 2007
11,251
It seems that you did not see the datasheet for the little 2N3904 transistors and you failed to make important calculations.

An NPN emitter-follower uses the transistor to pull up the signal but uses the emitter resistor to push the signal down. It works poorly when its load is less than 1/10th its emitter resistor value.

You are making a class-A heater instead of a class-AB audio power amplifier.
 

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Thread Starter

Zeeus

Joined Apr 17, 2019
481
It seems that you did not see the datasheet for the little 2N3904 transistors and you failed to make important calculations.

An NPN emitter-follower uses the transistor to pull up the signal but uses the emitter resistor to push the signal down. It works poorly when its load is less than 1/10th its emitter resistor value.

You are making a class-A heater instead of a class-AB audio power amplifier.
lol..Thanks(not trying to burn down my neighbourhood ..Although in my post, I said i would not be using 2n3904 for this. Did not build the circuit
 
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