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Old 20th December 2012, 07:14 AM   #11
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Gosh darnit I can't edit my own post again.
If anyone knows why I still have so much background noise (ahem.. detecting radio frequencies as well as useless static?)
I would really appriciate if you knew how to fix it.. I am completely lost as to why there's so much gain and noise.
I've tried literally everything.... every possible combination of adding a resistor... still loads of noise
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Old 20th December 2012, 07:38 AM   #12
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Chips like this have a very high internal gain and you need extreme care in the layout and wiring. Even a couple of centimeters wire at the input picks a lot of noise up.

You hear radio stations because the front end transistors in the chip work as diode demodulating the radio waves.
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Old 20th December 2012, 07:48 AM   #13
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okay how do I solve the extreme noise problem?
I have it hooked to 12 volt 2 amp power supply
it works amazingly well and puts out a pretty powerful sinewave signal to my 10 watt speaker..
the speaker is rated for 8 ohms and 10 watts
It really moves a lot
And I felt the chip after about a minute of running it..
not even warm! now that's what I call efficient! (well I do have a massive heatsink that's more than 100 times bigger than the actual chip itself so that's probably helping a lot)
the only problem is..... it has way too much background noise and it has way too much gain... if I could at least figure out why I can't change the gain...
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Old 20th December 2012, 08:07 AM   #14
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You need to read and understand how an opamp works.

Any noise will be down to the layout and construction and stability problems. Using chips like this is totally different to the simple low gain amplifiers you have used before. The gain of this IC is 43db which is around 160.

Why don't you post a picture of what you have done with it
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Old 20th December 2012, 09:57 AM   #15
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Yes please post a diagram or picture of your current setup.

Gain of the chip can be set with value of resistor connect between pin2 and ground.
In the data sheet, no such external resistor is shown, but inside the chip there is a 50 ohm resistor. If you connect pin2 directly to ground then you get maximum gain.

You can calculate the gain by the formula: Gain = 1 + Rf/Rnf
If you use the values in the datasheet you get Gain = 1 + 10000/50 = 201

If you add 1000 ohm between pin 2 and ground (you must remove connection from ground to pin 2 for this to work) Gain = 1 + 10000/1050 = 11.52

500 ohm gives you a Gain of 19.2 x

If you let pin 2 float, gain is reduced to 1x

Datasheet does not tell if this amp can handle unity gain or not, so there might be stability issues with low gains.

To remove RF interference, place a small cap (100pF to 1000pF) between pin 1 and ground.

When a resistor is used between pin2 and ground, you can also try to add 100pF from output pin4 to pin2 this will lower gain at very high frequencies, and maybe make it stable.

Try also to place a 100 uF capacitor between pin 5 and pin3 (ground), remember to connect correct polarity.

But please post a diagram or picture )

Last edited by BachAudioDK; 20th December 2012 at 10:12 AM.
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Old 20th December 2012, 04:59 PM   #16
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Oops... found out it's partially shorted.. useless now....
it was connected the basic way that you usually connect it in.. and I had a couple 1,000uF capacitors in parallel... so in total it was about 8,200uF's
that's for the speaker output... I know it's over doing it... but I wanted a huge amount of output power for my speaker.. so I could have the most low frequencys..
it worked amazingly well for the time it was working.. it easily went lower than 2hz
and a 2.2uF capacitor for the input worked great.
I did find out that I needed a resistor in series with pin 3 and the speakers negative
that made it sound nearly perfect and got rid of a huge amount of static
it sounded way better and it had much more power too
but I just could never lower the gain at all no matter how hard i tried
I tried all of what you said but it was always stuck at max gain
And what is a pF? I've never heard of such a measurement before.

I would post a picture but I don't have a working camera anymore (it broke D: )
the amp ran off of a 12 volt 2 amp power supply for a little while..
It worked great and never even got the slightest bit warm when playing at a high output power and it pumped the 10 watt speaker like i've never seen a home made amp do before!
and If I had the right components it would do more than 2x better probably
Once I get around to it.. I'll see if I can try what your saying out here.. since the little chip isn't wired up to anything anymore
I have some twist ties attached to it so I don't break the fragile leads because they're so weak

Last edited by realflow100; 20th December 2012 at 05:03 PM.
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Old 20th December 2012, 06:06 PM   #17
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pf is a Pico Farad. A very tiny amount of capacitance.

Farad - Wikipedia, the free encyclopedia
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Old 20th December 2012, 06:13 PM   #18
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I don't know what the use of such a tiny amount of capacitance would be useful for...O.o
I doubt it would even make any difference at all if I put it on or not
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Old 20th December 2012, 06:17 PM   #19
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Believe me, it makes a difference. A 10 or 20pf cap in the correct place is an essential part of many high powered amplifiers. Without such a cap the amplifier would oscillate and self destruct.
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Old 20th December 2012, 06:30 PM   #20
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sounds bad...
well doesn't hurt to try! I wonder where I would find a 100pF capacitor...?
Are those the disk capacitors?
I think I may have one but I have no clue what it's capacitance is..
maybe i could just try anyways if it works i'll tell ya
but now i got to put my amplifier back together... carefully... so i don't break the fragile leads of the little chip off..
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