Simple PC audio amplifier circuit

MrChips

Joined Oct 2, 2009
30,714
Look at the circuit in post #36. R4 is the volume control. Value of the pot is not critical, 1k to 20k will work, preferably a log taper pot.

In your circuit, C1 is too large. Use 10μF on the input.

I imagine that the quality and volume of that circuit would be very poor.
 

Thread Starter

tjohnson

Joined Dec 23, 2014
611
Look at the circuit in post #36. R4 is the volume control. Value of the pot is not critical, 1k to 20k will work, preferably a log taper pot.

In your circuit, C1 is too large. Use 10μF on the input.

I imagine that the quality and volume of that circuit would be very poor.
Thank you for your helpful reply. Regrettably I can't use the circuit in post #36, because I don't have a heat sink. Since R4 is the volume control in that circuit, would I need to add a resistor in the same place in my circuit for volume control, or is that the function of R2?

The volume in my circuit was pretty good, until I found out that I had to add 2-1k resistors to avoid shorting the audio input when converting it from stereo to mono. That reduced the volume by ~6 dB, which made it only about 57% as loud as it used to be.:(
 

MrChips

Joined Oct 2, 2009
30,714
You cannot alter the values of R1, R2 and R3 in your circuit because that will upset the DC bias of the circuit.

Instead of using two 1kΩ resistors to bridge stereo to mono, try two 100Ω.
 

Thread Starter

tjohnson

Joined Dec 23, 2014
611
You cannot alter the values of R1, R2 and R3 in your circuit because that will upset the DC bias of the circuit.

Instead of using two 1kΩ resistors to bridge stereo to mono, try two 100Ω.
Thank you! Changing the values of the resistors and capacitor as you suggested made a huge difference! Now my goal has been accomplished, since I can listen to audio across the room from my computer rather than always needing to use headphones.:cool:
 

Thread Starter

tjohnson

Joined Dec 23, 2014
611
One more question: Why do all the amplifier circuits that I've seen require a separate voltage source (like a 9V battery), but headphones don't? Is it because headphones don't really amplify sound at all, but merely play it?
 

MrChips

Joined Oct 2, 2009
30,714
In a way, you are correct.
Headphones are transducers and would be classified as a passive device.

An electronic amplifier is an active device and requires external supply to provide power amplification.
 
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