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PC Speaker PreAmp

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Tucson Annie

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Hi Guys,

As some of you know, I'm teaching myself about op amps and audio amplifiers and stuff....rather than just building others' circuits, I'm kinda starting from scratch to learn how they work...

So, I had this brilliant idea (just kidding) and thought I'd run it by the experts to see if I am on the right track....

I have a particular PC with an onboard sound card that I watch movies on sometimes. For some reason, when I watch old British mysteries (Lord Peter Wimsey or old Agatha Christie) the volume is so low that even with my powered speakers cranked up I have problems hearing....

So, my idea is to use an op amp chip to make a little amplifier to go between the sound card and the input to the powered speakers, a preamp if you will...

Things I will need to figure out are the output impedance from the sound card, the input impedance to my little powered speakers (they are 10 dollar cheapos) and I'm sure a bunch of other things.....

Let me say that I am NOT an audiophile.....I don't care how 'perfect' it sounds...and it doesn't have to be stereo....I'm talking about old made-for-tv mysteries from the 70s so the sound quality sucks anyway...I just want to be able to crank up the volume....

I know I need to be careful so I don't blow up my PC's sound card.....but other than that, am I missing something that would make this project a bad idea?

Thanks in advance!

Annie :)
 

Tucson Annie

New Member
Yes, Bill....they do have software running to make sure I am not an evil evil DVD pirate.... :) But this isn't about me solving the problem with Netflix, this is about having a 'real world' problem to solve using a circuit I'm going to design...it's a lot more fun learning when I know that what I build can be used for something meaningful....

Annie :)
 

audioguru

Well-Known Member
Most Helpful Member
A simple opamp can be used as a preamp. Its input impedance can be 47k or 100k to be driven from the output of any sound card and it can have an adjustable gain control trimpot. Its output impedance will be low enough to drive any amplified speakers.
 

blueroomelectronics

Well-Known Member
It's not that I thought you were a pirate, I live in Canada and don't even have access to Netflix streaming (I use an Apple TV and it works like a charm for video rentals).
Depending on what software you use it may have equitation settings to boost the audio.
 

Tucson Annie

New Member
Yay, Audio Guru! Thanks for the encouragement! I'll crack out a schematic now and breadboard something....

And Bill, I didn't think you thought I was a DVD pirate, I was just kidding and pointing out that I didn't care about resolving the problem with Netflix, I just wanted an excuse to make a circuit.... :)

Thanks, guys!
 

shimniok

Member
Curious to see what you come up with. It's on my list to learn about audio amplification. Are you thinking along the lines of LM386 then or standard op amp as suggested above? That's about all I know of audio op amps so far. I grew up in Tucson, btw. I find it easier to learn / do when I actually have a problem to solve, however unnecessarily complex -- or simply unnecessary -- my solution is...
 

audioguru

Well-Known Member
Most Helpful Member
Are you thinking along the lines of LM386 then or standard op amp as suggested above? That's about all I know of audio op amps so far.
An LM386 is a little power amplifier (not an opamp) with an output of 0.45 Watts into 8 ohms at clipping with a 9V supply. Its voltage gain is 20 but can be increased to 200 with an additional capacitor.

An opamp can drive a power amplifier (not a speaker) and can have a voltage gain of up to 200 at all audible frequencies.
 

Tucson Annie

New Member
I keep mixing up the 386 with the op amp...this is the second time Audio Guru has corrected that, lol....the reason I keep calling it an op amp is because in this book by Forrest Mims III that I have he has the 386 chip in the op amp section of the book....

Michael, I will draw a schematic of what I come up with when I work on it this weekend...I got sidetracked working on a square wave generator circuit and haven't gotten back to the preamp thingy.....You grew up in Tucson? I hated Tucson....I lived there for 6 years (grew up in Silicon Valley, moved to NYC, moved to Tucson, now live in Idaho) and it sucked....crime ridden, dirty, hot, boring...I practiced my second amendment right every day in Tucson....I felt safer in Brooklyn, lol.....but Idaho is nice, quiet, safe, friendly....sorry, I got a little off topic....

:)
 
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