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Old 20th December 2012, 01:00 AM   #1
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Default stuck on transistors again

i am attempting to build something like this http://hades.mech.northwestern.edu/i...l_follower.gif
for a simple push-pull amplifier..
but I only have one type of transistor.
Is it still possible?

By the way I found this type of transistor but I wanted to see how I could get it working the simplest way possible.
It's from a TV (and whoa my computer monitor just randomly got all stripey pink all over then fixed itself but that's off topic)
http://html.alldatasheet.com/html-pd.../2/LA4225.html

Last edited by realflow100; 20th December 2012 at 01:15 AM.
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Old 20th December 2012, 01:32 AM   #2
jaycee is offline jaycee  United Kingdom
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No - you need NPN and PNP

The device you pulled is not a transistor, it is an IC, a small audio power amplifier.
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Old 20th December 2012, 01:39 AM   #3
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okay so how do I hook it up properly?
I have the components for it

nevermind I got the IC working but no matter what I try.. I can't bias it properly at all D:
i tried using some various resistors but it makes no difference wherever i put them D:
maybe i still didn't put them in the right place
but the gain is still HUGE!
with a 5 volt DC power adapter the gain is so huge. it's working... but I need to bias the darn thing somehow...
i tried all combinations of resistors here and there...
it actually has the most sound without any resistors sadly..\
i'm stumped on why it's not working..

Last edited by realflow100; 20th December 2012 at 02:07 AM.
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Old 20th December 2012, 02:19 AM   #4
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Hi,

For the IC to work you need AC coupling caps Cin and Cout as shown on page 3.
To reduce gain you need to add a resistor in series from pin 2 to ground. Try 1k ohm.

Try to run on higher Vcc, 12volt to 20 volt.

Cheers

Last edited by BachAudioDK; 20th December 2012 at 02:21 AM.
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Old 20th December 2012, 02:28 AM   #5
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yes i got those put on it.... but they do not make much of a difference.. output still sounds blocky and square waved...
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Old 20th December 2012, 02:41 AM   #6
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Ok, then try to ad 50k ohm from Vcc to pin 1 and 50k ohm from pin1 to ground.
This will set DC point Vout to approx: gain x Vcc/2. To reduce DC gain to 1x put a cap(20-100uF) in series with resistor that you add in series with pin2
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Old 20th December 2012, 03:07 AM   #7
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ok now it sounds way better but there's a heck of a lot of buzzing!!! sounds like a buzz horn going off i can hear buzzing over 5 feet away!
How do I get rid of the crazy buzzing?
and the gain is still extremely high..
My PC's volume is set to 0% and I can hear it clearly coming from the speaker..

Last edited by realflow100; 20th December 2012 at 03:22 AM.
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Old 20th December 2012, 03:49 AM   #8
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oh since I can't edit my own post
I wanted to ask..
How exactly do I seriously lower the gain of this amplifier chip?
I tried putting 12 volts for it for a split second but it made my speaker just go in a frenzy of static and jumping over my table because the gain is absurdly high
so with only 5 volts it's perfectly stable. but still has a huge amount of useless static in the background..
and my computers volume has to be at like under 5% for it to sound clear
it sounds perfect at 4% but I don't like the static that I continuously hear in the background
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Old 20th December 2012, 04:30 AM   #9
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Are you 14 years old? Serious.
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Old 20th December 2012, 05:32 AM   #10
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No. I just turned 15.

And now I can hear a totally random radio station now when I put a resistor in series with the input wire. and it's clearly audible
anyone listen to the radio and hear band aid brand advertisements and some kind of weird music?
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