How does it work? I have the possiblility of buying a big pro amp, but one chan has failed and the clip light stays on. Logic suggests that the clip circuit is shutting down the input. So if I fixed it or bypassed it, the amp would work.
I searched the threads but all I found out was that you guys don't use them much.
I searched the threads but all I found out was that you guys don't use them much.
Usually the 'clipping sensing/protection' is done by 'monitoring' the current passing through a low value resistor (say 0.1 to 0.22 ohms or so) placed either on the output devices emitter (source when mosfet) or on one of the amp's rails.
So I guess if the clipping indicator light is on at all times then too much current is passing trough that particular resistance, this could mean ugly stuff like fried output devices and so on.
So I guess if the clipping indicator light is on at all times then too much current is passing trough that particular resistance, this could mean ugly stuff like fried output devices and so on.
Hmmm. So I could narrow down the possibilities by disconecting the path out of the protection circuit?
Also a blown FET wouldn't kill the rest of the amp because the curent limiter would have shut it down before then?
I need to hit the books about dead FET diagnosys. I would ask for help on here but the audiophiles would kill me for being lazy!
Also a blown FET wouldn't kill the rest of the amp because the curent limiter would have shut it down before then?
I need to hit the books about dead FET diagnosys. I would ask for help on here but the audiophiles would kill me for being lazy!
Actually most professional audio amps use a comparator on the outputs and Crowns in particular use a distortion detector that tracks the waveform in and out of the amp, also a kind of comparator. Some are VERY good at stopping such problems as shorted output devices from taking out any anything else by turning off the HV rails if the comparators throw up a red flag.
Clipping has been tackled from the 60 s in various ways ,
now adays the clippng detection and correction network is very - advanced -
not simle active changing of the amplification factor of the amplifier - ratios are done anymore
as mentioned earleir there are multiple input to output comparate circuits + just input comparator circuits alone to keep the signal - highly clean before reching the amps
if you have a new amp something made after 2000 you can yet by - pass all this - sometimes - and only run the out put section
but amps earlier on have detection circuits built in to the differential pairs on the main amp input circuit - which in turn throgh opto coupler s ets - some times change the amplfication factor of the amps - ther by protecting it - till the clipping is limited - by the user
these are difficult to be by passed easily & succesfully without (other damage)
the qs you have posed is diffcult to approach as there are various options to clipping limit circuits in use
my advise would be - that you sit down with varios schem from different manufactureres and compare all - by doing so ull recognize patterns and get a great idea of how this works
i am pasting an artice from the PEAVEY site to emphasise how serious amp manufactureres consider - clipping is , in fact some of the basic out - put stages have not changed over the years
there DDT tech is described further on
and all of the mods have been done it this stage - the clipping detection and improvement
from Peavey -
When a signal has waveform peaks that exceed the electronics' power-supply rails or signal swing, that waveform will get chopped off, or "clipped." This condition can occur for a number of reasons, but the most common is applying too much gain to a signal. Clipping is undesirable, as it is an obvious alteration, or distortion, of the waveform.
The audibility of clipping depends upon the degree. We're all familiar with the sound of severe clipping as experienced with a boom box on weak batteries or the typical car radio turned up too high. The common mechanism there is an amplifier limited to modest battery voltage. Light clipping, on the other hand, is much more difficult to characterize. The audibility of light clipping depends greatly on the signal being clipped. A sine wave, or pure tone, as long as it is below a few kilohertz, will generate audible harmonics, or overtones, discernible as additional frequencies. If a 10 kHz tone is clipped, the first harmonic is 20 kHz and not very audible.
This should not be interpreted to mean that clipping is not important at high frequencies. Real-world music signals typically contain high- and low-frequency signals simultaneously. Often, the high-frequency signal that clips is riding on top of a low frequency. This modulated clipping creates low-frequency intermodulation products that are very audible. The more common example of this is nasty FM radio stations that overcompress. Compression raises the low-level sibilants (s and f sounds) until they clip at later stages. This is aggravated by widespread use of pre/de_emphasis, where high frequencies are boosted and then later cut to reduce noise. While this relies on the fact that high frequencies do not naturally occur at high levels, it's not nice to fool mother nature.
In general, the more complex the sound, the less audible the clipping. Light clipping of transients will in fact increase the apparent high-frequency content and give the sound a little more edge. One obvious exception is the human voice. While the voice is a very complex signal, our hearing is highly attuned to voice frequencies, and we have daily reminders of what undistorted speech sounds like.
OK, what does this mean to me? It depends upon your application. If you're making an archival recording of a flautist (flutes like to put out clean sine waves), you need to record as cleanly as possible. If you're mixing Axel Motif's YMCA rap gig, you might be improving the sound to let it clip a little. As with everything else in life, there are tradeoffs. If you run your signal too far below clipping, you will not get a good signal-to-noise ratio. Most Peavey products are calibrated to fire the clip LEDs a few dB before clipping, so occasional firing of a clip LED means you are hitting the channel hard enough to get a good S/N and not distort the sound. If you're mixing on that other guy's mixer, by the time you get clip LEDs, your signal is toast. Always use your ears to back up your eyes.
To help you in your task of accurately reproducing sound without clipping-induced distortions, we incorporate DDT™ into our power amplifiers. DDT senses clipping (or current limiting) and reduces the gain to prevent audible distortion. In mixers we provide metering and clip/OL indicators. Recently, competitors' advertising has made a big deal about "headroom." One would be led to believe from the frequency of such statements that they somehow have more headroom than others—not so. Most contemporary mixer designs share similar limitations, namely, the power-supply voltages. The voltages are further defined by the integrated-circuit technology. Most general-purpose ICs are manufactured with a 36V process; this limits the power supply to +/-18V max. The more conservative approach, +/-15V rails, costs a mere 1.5 dB of headroom for increased reliability. There will be small to nonexistent headroom differences between competing mixers. Why the perceived difference?
One dirty trick competitors use is cheating the clip indicator to understate how much a signal is clipping. As light clipping is not very audible, and the ad said they have more headroom, they get away with it. One prominent manufacturer (who shall remain nameless) goes as far as not sampling after the fader gain stage in his input channel. This means you could be clipping as much as 10 dB before the LED lights up. This same manufacturer also doesn't sample at multiple points (we sample at preamp, EQ, and post fader). Any cut in the EQ will allow the preamp to clip before showing up on the clip indicator. (Note: when using PFL to gauge headroom, keep in mind that it won't show the 10 dB of gain in the fader stage.)
Just for fun, if you know someone who foolishly bought a non-Peavey mixer, get them to try this test. While talking into a microphone plugged into an input with the fader up at maximum, slowly increase the mic preamp gain while listening to the output. If your friend is unlucky enough to have the wrong mixer, you will hear severe clipping distortion long before the clip light indicates. This falls under the category of fooling all of the people some of the time, and some of the people all of the time.
It would be easier (and cheaper) for us to remove the multiple-point-sampling clip circuitry, but it isn't the right thing to do. We have cultivated a long-term relationship with our customer base by giving them honest, accurate data and will continue to do so. We believe they can't fool all of the people, all of the time. The marketplace will figure out who's telling the truth
- XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
suranjan
transducer design engineer
now adays the clippng detection and correction network is very - advanced -
not simle active changing of the amplification factor of the amplifier - ratios are done anymore
as mentioned earleir there are multiple input to output comparate circuits + just input comparator circuits alone to keep the signal - highly clean before reching the amps
if you have a new amp something made after 2000 you can yet by - pass all this - sometimes - and only run the out put section
but amps earlier on have detection circuits built in to the differential pairs on the main amp input circuit - which in turn throgh opto coupler s ets - some times change the amplfication factor of the amps - ther by protecting it - till the clipping is limited - by the user
these are difficult to be by passed easily & succesfully without (other damage)
the qs you have posed is diffcult to approach as there are various options to clipping limit circuits in use
my advise would be - that you sit down with varios schem from different manufactureres and compare all - by doing so ull recognize patterns and get a great idea of how this works
i am pasting an artice from the PEAVEY site to emphasise how serious amp manufactureres consider - clipping is , in fact some of the basic out - put stages have not changed over the years
there DDT tech is described further on
and all of the mods have been done it this stage - the clipping detection and improvement
from Peavey -
When a signal has waveform peaks that exceed the electronics' power-supply rails or signal swing, that waveform will get chopped off, or "clipped." This condition can occur for a number of reasons, but the most common is applying too much gain to a signal. Clipping is undesirable, as it is an obvious alteration, or distortion, of the waveform.
The audibility of clipping depends upon the degree. We're all familiar with the sound of severe clipping as experienced with a boom box on weak batteries or the typical car radio turned up too high. The common mechanism there is an amplifier limited to modest battery voltage. Light clipping, on the other hand, is much more difficult to characterize. The audibility of light clipping depends greatly on the signal being clipped. A sine wave, or pure tone, as long as it is below a few kilohertz, will generate audible harmonics, or overtones, discernible as additional frequencies. If a 10 kHz tone is clipped, the first harmonic is 20 kHz and not very audible.
This should not be interpreted to mean that clipping is not important at high frequencies. Real-world music signals typically contain high- and low-frequency signals simultaneously. Often, the high-frequency signal that clips is riding on top of a low frequency. This modulated clipping creates low-frequency intermodulation products that are very audible. The more common example of this is nasty FM radio stations that overcompress. Compression raises the low-level sibilants (s and f sounds) until they clip at later stages. This is aggravated by widespread use of pre/de_emphasis, where high frequencies are boosted and then later cut to reduce noise. While this relies on the fact that high frequencies do not naturally occur at high levels, it's not nice to fool mother nature.
In general, the more complex the sound, the less audible the clipping. Light clipping of transients will in fact increase the apparent high-frequency content and give the sound a little more edge. One obvious exception is the human voice. While the voice is a very complex signal, our hearing is highly attuned to voice frequencies, and we have daily reminders of what undistorted speech sounds like.
OK, what does this mean to me? It depends upon your application. If you're making an archival recording of a flautist (flutes like to put out clean sine waves), you need to record as cleanly as possible. If you're mixing Axel Motif's YMCA rap gig, you might be improving the sound to let it clip a little. As with everything else in life, there are tradeoffs. If you run your signal too far below clipping, you will not get a good signal-to-noise ratio. Most Peavey products are calibrated to fire the clip LEDs a few dB before clipping, so occasional firing of a clip LED means you are hitting the channel hard enough to get a good S/N and not distort the sound. If you're mixing on that other guy's mixer, by the time you get clip LEDs, your signal is toast. Always use your ears to back up your eyes.
To help you in your task of accurately reproducing sound without clipping-induced distortions, we incorporate DDT™ into our power amplifiers. DDT senses clipping (or current limiting) and reduces the gain to prevent audible distortion. In mixers we provide metering and clip/OL indicators. Recently, competitors' advertising has made a big deal about "headroom." One would be led to believe from the frequency of such statements that they somehow have more headroom than others—not so. Most contemporary mixer designs share similar limitations, namely, the power-supply voltages. The voltages are further defined by the integrated-circuit technology. Most general-purpose ICs are manufactured with a 36V process; this limits the power supply to +/-18V max. The more conservative approach, +/-15V rails, costs a mere 1.5 dB of headroom for increased reliability. There will be small to nonexistent headroom differences between competing mixers. Why the perceived difference?
One dirty trick competitors use is cheating the clip indicator to understate how much a signal is clipping. As light clipping is not very audible, and the ad said they have more headroom, they get away with it. One prominent manufacturer (who shall remain nameless) goes as far as not sampling after the fader gain stage in his input channel. This means you could be clipping as much as 10 dB before the LED lights up. This same manufacturer also doesn't sample at multiple points (we sample at preamp, EQ, and post fader). Any cut in the EQ will allow the preamp to clip before showing up on the clip indicator. (Note: when using PFL to gauge headroom, keep in mind that it won't show the 10 dB of gain in the fader stage.)
Just for fun, if you know someone who foolishly bought a non-Peavey mixer, get them to try this test. While talking into a microphone plugged into an input with the fader up at maximum, slowly increase the mic preamp gain while listening to the output. If your friend is unlucky enough to have the wrong mixer, you will hear severe clipping distortion long before the clip light indicates. This falls under the category of fooling all of the people some of the time, and some of the people all of the time.
It would be easier (and cheaper) for us to remove the multiple-point-sampling clip circuitry, but it isn't the right thing to do. We have cultivated a long-term relationship with our customer base by giving them honest, accurate data and will continue to do so. We believe they can't fool all of the people, all of the time. The marketplace will figure out who's telling the truth
- XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
suranjan
transducer design engineer
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