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Amplifying AC voltage via DC supply voltage

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Pixel_95

New Member
Hi all,

at the moment I'm trying to amplify an AUX-Signal with a 12V DC supply
voltage. I tried die setup from here as u can see in the picture below.

But all I get is just an annoying noise sounding horrible.

For the amplifier I used both the CA3240EZ and the OPA134PA.

Maybe my grounds are not connected correctly.

It would be awesome, if anyone could help me out.
 

crutschow

Well-Known Member
Most Helpful Member
Do you have a 0.1μF ceramic decoupling capacitor directly from the +12V power pin to the ground pin?
 

audioguru

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I betcha it is built with messy long jumper wires (antennas) on a solderless breadboard.
 

dr pepper

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Welcome pixel.
I see the input impedance is quite low, and the output capacitance is high.
As cruts says you need a cap across the supply pins of the ic, a 10u and a 100n ought to do it.
What kind of noise do you get, hum, hiss?
 

alec_t

Well-Known Member
Most Helpful Member
What is the source of your AUX_IN signal and what are you feeding the AUX_OUT signal into?
What are you using as a 12V supply?
 

Pixel_95

New Member
To answer all your question at once:

I tried now those to power supply bypass capacitors, I found in the interet:
1st:


2nd:

@dr pepper:
which capacitor and which resistor shell i change? and whats i your suggestion for the new value?
And the noise sound like this: Subwoofer-Noise at Soundcloud

@alec_t:
AUX in comes directly from my DVD receiver, and AUX IN goes directly into my subwoofer.
As a 12V voltage supply I use an charging device with 12V, 2A (12V are tested with my voltmeter)
 

audioguru

Well-Known Member
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The "noise" is obviously extreme even-harmonics distortion and the 'scope shows the positive peaks are normal but the negative peaks have reduced levels. It might be caused by the low impedance input of the inverting opamp circuit overloading a source that pulls up well but pulls down poorly. At the end of your soundcloud recording there is a group singing (in Spanish?) with auto-tune correcting the pitch of their voices.
 

Pixel_95

New Member
At the end of your soundcloud recording there is a group singing (in Spanish?) with auto-tune correcting the pitch of their voices.
The song was five more hours - chris brown. And what you here is only the subwoofer, but it might be, that at the end one can here some voices.

It might be caused by the low impedance input of the inverting opamp circuit overloading a source that pulls up well but pulls down poorly.
So you mean I shell change R3 and R1 to lets say 100kΩ?
 
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audioguru

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The schematic in your first post has 22k for the R1 feedback resistor so the gain of the circuit is 22k/2.2k= 10 times.
The second circuits you show have 2.2k for the R1 feedback resistor so the gain of the circuit is 2.2k/2.2k= 1 time (no gain like a piece of wire) but the signal is inverted.
The feedback resistor has nothing to do with the input impedance. The distortion might be caused by the inverting circuit has an input impedance that is too low but if you increase the value of the input resistor R3 then the gain is reduced unless you also increase the value of R1 but you do not want R1 to be as high as 1M because stray capacitance might cause oscillation.

Why don't you make the non-inverting circuit that has a 100k input impedance and a gain of 10 times??
 

tcmtech

Banned
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I tried die setup from here as u can see in the picture below.

From the link.



To me, the sound you have recorded implies that either the IC is being way over driven or you have blown one of its output devices.

Does the amplifier work when configured in the noninverting circuit?

Why are you trying to invert your signal anyway?
 
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alec_t

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goes directly into my subwoofer.
Is that just a naked speaker, or is it an amplifier driving a speaker?
The IC can only source/sink up to ~35mA. What is the input impedance of the subwoofer?
 

audioguru

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An opamp cannot drive a low impedance speaker. You need a power amplifier to drive the speaker. The opamp was limiting its current which caused the severe distortion.
You said "the" song was Five More Hourse but that was your song and I talked about the song that played after your song that was an Acapello by Daddy Yankee.
I couldn't find Five More Horses but instead I found Five More Hours and the You Tube video has many pretty young ladies:
 

MrAl

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Most Helpful Member
What I tried now is this:


Still get the noise ... maybe I should try the non inverted one ...

Hi,

Sounds like you are getting very bad clipping.

We need to know EXACTLY what you have connected to the input, and what you have connected to the output, or else we can only guess what is causing this. You need to specify these two things.
 

audioguru

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Another problem with the opamp circuit trying to drive a speaker is that the output capacitor passes only high frequencies. 100uF feeding a 4 ohm speaker cuts off frequencies below 400Hz.

If the opamp limits current to 35mA then 35mA is the peak but 24.7mA is the RMS current. The maximum undistorted power into a 4 ohm speaker is only (24.7mA squared) x 4 ohms= 2.4mW which is a VERY low level. you turned up the volume too much.
For 10W the RMS current must be 1.6A and the peak current must be 2.4A. Then the current is 100 times more.
 

Pixel_95

New Member
Ok, I'll try my best to describe you guys my setup.

I get the via an normal chinch cable going into the receiver of a LG HT44S. From there i use the subwoofer output with the orange and black cable as you can see here:
Then this black and white cables go into my breadboard in here. (other View of the breadboard here)
And afterwards the outputs goes to the subwoofer in here.

Hope you got now all information you need.

If my curcuit is compete crap, maybe you could just tell me the simplest way to amplify an audio signal going into my 3ohms subwoofer.
 
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audioguru

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You are blowing up the input of the opamp with a signal level that is much too high for it and you are overloading the output of the opamp with a load resistance that is much too low for it.
Why do you want to amplify the subwoofer signal? If you want more power then you need a more powerful amplifier and a larger subwoofer speaker. On a normal stereo you add the preamp at the INPUT of the subwoofer power amplifier, not at its output. But this system does not have an input to the subwoofer power amplifier, it is inside the circuit after a lowpass filter.

It is a fairly cheap audio system. The LG website says it is discontinued. It has a small speaker wrongly used as a subwoofer and an amplifier with fairly low power .

The subwoofer speaker is a little 5" woofer driven with an amplifier with an output of 170 Whats which is only 22 Watts. They say it is for a small room.
Replace the entire audio system with a subwoofer that has a 10" or 12" speaker driven with hundreds of real Watts, not Whats.
 

tcmtech

Banned
Most Helpful Member
If my curcuit is compete crap, maybe you could just tell me the simplest way to amplify an audio signal going into my 3ohms subwoofer.
So what are you trying to gain by doing this? o_O

You have a 170 watt rated subwoofer output going into a sub 1 watt IC to drive the speaker? Why???????????????? :confused:

If you want more power you need to be using Op- Amp circuits or complete IC designed for high power operation like this one, http://xtronic.org/circuit/amplifie...93-200-watts-rms-total-includes-power-supply/ , that's built around something like the TDA7293 IC set for a basic example or if you want to go nuts with the wattage you need to look at designing and building dedicated circuitry like this basic 500 watt , http://circuitschematicelectronics.blogspot.com/2012/04/500w-power-amplifier-with-2sc2922.html , amplifier circuit uses. ;)
 

audioguru

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Most Helpful Member
The ad does not mention Digital amplifier nor class-D so it must be class-AB. Its efficiency might be 50%. They say the total power is 440 Whats (a lie) with 170 Whats for the sub-woofer and each satellite speaker gets 135 Whats. They also say the "consumption" is 110 Watts then its real total amplifier signal output is 55 Watts and the other 55 Watts is heat. The subwoofer gets a division of the total output that is 170W/440W= 0.3864 times the 55 Watts real total output= 21.2W. Each satellite speaker gets 135W/440W= 0.3068 times the real 55W= 16.9 Watts.
LG is Lucky Goldstar and is Korean.

The subwoofer enclosure is said to be 190mm wide (7.5") and the woofer speaker is shown to be using most of it, about 5" or 6" in diameter. They say the speaker system is for a small room..
 
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