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Improper adjustment of gains (pre-amp circuit) can cause the input to the actual amplification circuit to be greater than its limits.

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(d) What causes "blown" amplifiers?

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Well, "blown" is not really a techinal term it can mean anything from distorted output - to no output. Generally, only three things can happen in an electronic curcuit:

A component "shorts" - an unintended, low resistance (example: a cap shorts, directly connecting the signal on the two sides together);

A component "opens" - a disconnection of a conductor (example: a winding (wire) in a transformer heats up an melts, breaking the circuit);

Or the component changes it's operating parameters (example: the actual PN junction inside a transistor is forced to pass too much current; not enough to short or open it, but enough change the way it works .... as if you tightened the lug nut on a car tire enough to crack/distort the stud but not enough for it to break off.)

~Manny.

"And you...Deja Vu...I'll always remember you!"
Hillary in Top Secret

(a) What exactly is clipping? Basically, it is like trying to stuff 10 lbs of manure in a 5-lb bag. You have to clip some manure off to make it fit. The BOTTOM picture of the two shows what a clipped sine wave looks like, and the TOP shows what it a clean sine wave is supposed to look like..

(b) What causes it? Over-driving the amplifier's circuitry, or a malfunction within the circuitry.

(c) Just how does it harm loudspeaker drivers? Inductive loads have AC resistance called "Reactance." Inductive reactance is the product of 2 pi times the frequency times inductance. The clipped portion represents no change in magnetic fields. The inductive reactance then turns into a non-inductive load (resistive) which could cause the voice coils to burn out if the DC component is strong enough or applied long enough.

If you apply a high enough DC to an inductive device, it'll toast it.
In addition to the information others posted, I hope this helps.

Jeff said:

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"Highly clipped audio is also rich in high frequency harmonic energy. This won't do your high frequency drivers any good."

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Indeed, it is.

A pure square wave is comprised of the fundamental frequency and an infinate number of odd harmonics. The more odd harmonics, the squarer it will be.

A sawtooth waveform is comprised of the fundamental frequency and an infinate number of even harmonics. The more even harmonics, the more linear rise the sawtooth's ramp will be.

Hey, guys...I am going on what my memory says from about 44 years ago...so please feel free to correct me if I am in error. I cannot recall what a fundamental frequency containing an infinate order of odd and even harmonics look like. Anyone know? A back-to-back sawtooth? I don't remember....

The pictures taken by Paul show nicely that a clipped signal has the same amplitude as the unclipped, but since it covers a bigger area, it also contains more energy and is therefore perceived as being louder. In addition to this, the square waveform elements contain odd harmonics and the signal is distorted.
It has to be understood that analogue components do not simply go into hard clipping from a certain point onwards, but that the signal gets more and more distorted as this point is approached. Equipment driven at the very edge of its performing abilities delivers distorted sound which is subjectively heard as louder than the undistorted.
A lot of the endless discussion about playback levels in cinemas is caused by equipment which is too weak and delivers distorted noisy sound which appears to bee too loud even when the SPL meter says the level is OK.
In digital equipment, all clipping is hard clipping, because when the maximum amplitude value is reached (all bits=1), there is no further headroom. Often, digital processors do not get properly aligned because people set the gain factor at the amplifiers to reach the specified sound pressure level with pink noise. If you then equalise by raising more than lowering individual frequency bands, the processor output is doomed to go into hard clipping when you there are signals approaching full scale, because the digital channel sum is above 0dB. To avoid this, you need amplifiers which can give you more gain so that you can lower more frequency bands in the digital equliser. And of course, the amplifier needs enough power reserve to handle full scale signals which are 20dB above reference level without clipping or even approaching clipping.
Most sound systems I know do not meet those requirements and as a consequence deliver noisy sound which is "too loud". If you ever have the opportunity to hear a system with enough power reserves and proper alignment in the digital and analogue areas, you will be very surprised by how "not too loud" movies played back at reference level are.
Another commonly neglected factor is the effectiveness or sensitivity of the loudspeaker, that means how much electrical power you need to reach a given sound pressure level. But that`s another subject...
Michael

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Hey, guys...I am going on what my memory says from about 44 years ago...so please feel free to correct me if I am in error.

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