# signal clipping

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#### chinsoon

##### New Member
hi there,

i am supposed to build a circuit that clips a signal source (signal generator) output to a voltage range of +/- 1V. this voltage range will then be used as input to a sound card. thats why i need to make sure that the input voltage to the sound card must not exceed 1V peak.

i was thinking of using diodes where i used to see it on other circuits, connecting the output to the rail or something. but i could not get the precise design out.

any idea how can i do that? or any BETTER idea on how to clip the signal at 1V

thanks

#### Grossel

##### Well-Known Member
One method is using a special version of a opamp voltage follover, where you put in a diode like pic below:

However, this only limits the maximum positive voltage. You need to design a "reverse" circuit where the diodes shifts directions and you'll us -1 volt on the Vlimit input.

#### Roff

##### Well-Known Member
Is the purpose of the clipper to protect the sound card from damage?

#### chinsoon

##### New Member
yup.. its to protect the sound card.

i have seen some circuits that look like this:
Opamp Voltage Limiting

this example was given as a internal block of an op amp.. i wonder is it a usable circuit, or its just simulation of concept. but somehow i have seen that diode configuration in some NAND gates... 74SL family i guess...

any idea how it is done to clip a voltage of +/- 1V?

#### Mikebits

##### Well-Known Member
diode clipping will create bad distortion. Would the nominal signal be under the threshold of the diodes.

#### Roff

##### Well-Known Member
This will clip at ±1V. It will also severely distort the signal if the input signal swings past ±1V. If you don't need high input impedance and low output impedance, you can omit U1a and U1d, and use a dual (TL072) op amp. The +1 and -1V references can be high resistance voltage dividers.
The supply voltages can be as high as 15V each, and they don't have to be equal in magnitude.

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#### audioguru

##### Well-Known Member
Somebody might like the severe distortion as FUZZ for their geetar.

#### chinsoon

##### New Member
hmm...

i just remembered that i have seen the op amp circuits before...

but this circuit will just work fine right?

if i connect any circuits to the soundcard, should i take care of the current that will be flowing into the soundcard? -- even if i have limited the soundcard input to +/-1V?

____________________________________________________________________________

anyway.. we're next asked to design another buffer/driver circuit that will be used as a driver to drive a load based on the output of the sound card...

my question is:

as i know, the output from the sound card has a very small current and voltage... so correct me if i am wrong, i need to design an amplifier (probably an op amp) to amplify the voltage, followed by a current buffer (probably a common base BJT configuration) to drive the load?

i just need to get a rough idea because its a design course, so the exact load and requirements of the design will only be disclosed when i attend the lab session.

thanks for all the help guys

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#### audioguru

##### Well-Known Member
An audio amplifier is used to drive a low impedance speaker.
You can make your own audio amplifier with an opamp driving some transistors, or use an audio amplifier IC.

Usually an audio amplifier has complementary emitter-followers at the output for equal push-pull high currents into a speaker.

#### chinsoon

##### New Member
yeah.. thats what i thought... normally speakers have around 4 ohm impedance...

so i would assume that it silly to connect the sound card output to an op amp since an op amp offers a very high input impedance? i was thinking that i might need to amplify the signal out from the soundcard, then connect a buffer to it

note: the driver circuit might not be used to drive a speaker. so far what we have done was to do data acquisition using the soundcard, and use a computer software to analyze the signal. the next part would be to use a soundcard to drive a load without loading the soundcard.

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#### audioguru

##### Well-Known Member
Home speakers are usually 8 ohms. Car speakers are usually 4 ohms but the ones in my car are 2 ohms for high current and high power.
Use an opamp to amplify the output of your sound card if you want.
Use an audio amplifier if you want.