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  1. #1

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    Default class A/B or D-class?

    I have been playing with car stereo installs for 30 years always had A/B type amps untill about a 3 years ago I bought my first class-D its a kicker 350 watt mono .
    I like the non dimming head lights but is it just me or does it not sound as clean ?
    It hits goes loud but the overall clarity of the bass is just not there ?
    I noticed this almost instantly ..

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    Only had 1 A/B amp powering my sub (2-channel bridged) and no, didn't hear any difference after switching it to D mono.
    There shouldn't be any hearable differences when it comes to lows... according to paperwork at least.

    Did everythign else stay the same after you install D mono? Cut off, sub, enclosure, rms, location, car....

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    I agree. I"ve been in the business for about 25 years and finally switched to a JL HD9005last year due to space constrictions (regular cab Toyota Pre Runner). Previously I ran Soundstream Reference 500 and Class A6.0 (used for 12 years). After that went with ZED Audio. I like the power and the sound is good but not great like I had before. Not as warm.

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    There's not gonna be any difference. Some class D amps have a higher noise floor but you're not gonna hear it thru a sub. If the bass isn't as clean, the problem is gonna be somewhere else like with the enclosure or something.
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    Default sound diff

    Quote Originally Posted by Vital View Post
    Only had 1 A/B amp powering my sub (2-channel bridged) and no, didn't hear any difference after switching it to D mono.
    There shouldn't be any hearable differences when it comes to lows... according to paperwork at least.

    Did everythign else stay the same after you install D mono? Cut off, sub, enclosure, rms, location, car....
    Same sub same car pulled the hafler MA1 put in the kicker 350 ..

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    Default dclass

    Quote Originally Posted by Installer4life View Post
    I agree. I"ve been in the business for about 25 years and finally switched to a JL HD9005last year due to space constrictions (regular cab Toyota Pre Runner). Previously I ran Soundstream Reference 500 and Class A6.0 (used for 12 years). After that went with ZED Audio. I like the power and the sound is good but not great like I had before. Not as warm.
    I thought it was me but installerforlife mirrors my thoughts .
    " not as warm is it" The amp I pulled is a gem the hafler MA1 .
    I build lots of home stuff to maybe thats why I picked it up ?
    I bet if it was just a sealed ok 10" it may not sound to diff but my ported L5 yea it was there .

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    Default dclass

    Quote Originally Posted by Vital View Post
    Only had 1 A/B amp powering my sub (2-channel bridged) and no, didn't hear any difference after switching it to D mono.
    There shouldn't be any hearable differences when it comes to lows... according to paperwork at least.

    Did everythign else stay the same after you install D mono? Cut off, sub, enclosure, rms, location, car....
    As far as paperwork what about signal to noise freq response and slew rate ??
    One thing that changed was I used a 2way elec xover w/the hafler .
    All else the same

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    Power can also be affecting things. Just because amp A says 100 watts and amp B says 100 watts doesn't mean they'll be the same. Some hit 100 watts at .5% THD, some at 1% THD it whatever. Also, the gain settings arent gonna be the same so setting 2 different 100 watt amps at the same gain postition won't give the same results.

    That could be the difference that youre hearing. Sub bass is gonna differ more in impact and tightness. Bright or warm arent gonna be characteristics of 20-80 Hz.
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    btw - what frequency is the "limit" for using D-class amps?

    Let's say i need an amp for midbass speakers that will be playing (strictly theoretical here) 80-250Hz. Is class D still good enought for these "just above sub" frequencies?

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    I wouldn't use a Class D meant for subs for anything over 160 personally. Those are meant for subs and are the ones with higher noise floors.

    Now there are different full range Class D amps out there that are clean as the wind driven snow. Those would be your best bet. They cost more than their Class AB counterparts tho. The benefit is the D's will be much smaller and much more effecient.
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    Default class-d

    Quote Originally Posted by MacLeod View Post
    Power can also be affecting things. Just because amp A says 100 watts and amp B says 100 watts doesn't mean they'll be the same. Some hit 100 watts at .5% THD, some at 1% THD it whatever. Also, the gain settings arent gonna be the same so setting 2 different 100 watt amps at the same gain postition won't give the same results.

    That could be the difference that youre hearing. Sub bass is gonna differ more in impact and tightness. Bright or warm arent gonna be characteristics of 20-80 Hz.
    One other thing class-d has no headroom , a 100 watt class-d has 100 watts TOTAL wheras a good a/b type may have as much as 4 db headroom so every 2 db is twice the power so you MAY get 400 watts PEAK , it may be noisy 400 watts but a sub cant really pick that up as bad as say a midrange would .
    So comparing 2 100 watt amps one beong a D-class one being A/B type may not really be fair unless you take that headroom into account .

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    Quote Originally Posted by 20hz View Post
    One other thing class-d has no headroom , a 100 watt class-d has 100 watts TOTAL wheras a good a/b type may have as much as 4 db headroom so every 2 db is twice the power so you MAY get 400 watts PEAK , it may be noisy 400 watts but a sub cant really pick that up as bad as say a midrange would .
    So comparing 2 100 watt amps one beong a D-class one being A/B type may not really be fair unless you take that headroom into account .
    Pretty sure that's not right. Every class D amplifier I've owned has had quite a bit of peak headroom. The crappy ones usually don't, but I don't put crap gear into my car. It's usually not 100% extra power, but that shouldn't be an issue in the first place. When it comes to the application of a Class D amplifier, which is nearly always for your subwoofer, the best move you can make is to choose an amplifier whose maximum unclipped RMS wattage is around the subwoofer's peak capability. That way the subwoofer is pretty much guaranteed an unclipped signal, increasing the longevity of your driver, and allowing your amplifier to run cooler. That being said, I can't say I've found an A/B amplifier that had a clean 133.3% extra power at peak volume, or even that much distorted. Also, like I mentioned earlier, you're better off not having to dip into your amplifier's peak power. You're better off guaranteeing yourself the unclipped signal by having more than enough amplification.

    And the rule for decibels is every 3 dB = double amplification power (The Loudspeaker Design Cookbook, 6th edition, pg 13, 2nd col., ln. 11, as well as every physics class I've taken).

    Class D amplifiers are perfect for subwoofers where the noise of the switching circuitry isn't an issue, and efficiency is necessary because of the higher amount of power required in comparison to a component set or coaxial set.

    There's nothing wrong with an A/B high-current amplifier for subwoofers. Done it before, and it absolutely kicked @5$. However, it's generally not worthwhile because the current demands become so high, and the average consumer's car can't handle a good A/B high-current amplifier. The amplifier I had ended up requiring a total overhaul of my electrical system so that I wouldn't keep experiencing voltage drops. Does the average car audio enthusiast want to have to replace their battery with one specifically designed for car audio, swap up to a high-current alternator, and do a Big Three upgrade to their electrical system? No. They want to go to Best Buy, and have it done quick, cheap, and simple.

    Back to the subject at hand, there are Class D full-range amplifiers out there, but they are generally more expensive than a comparable A/B amplifier, and the added cost really isn't justifiable. The typical wattage-per-channel for the HF drivers that the average car audio enthusiast shoots for is 100, give or take, typically via 4 channels, which doesn't draw all that much current, therefore you really don't need Class D amplification in that situation.
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    No amps have "head room". Different companies rate their amps differently. Pay attention to the THD number, this is kinda like an RPM gauge and shows you how hard the amp is being pushed at that rated number. So an amp that does 100 watts at .5% THD might do 130 at 1%.

    Headroom would be determined by gain settings. If your gain is set low, you'll have tons of headroom cause your volume knob will always be behind the amps input. If you have the gains too high, your amp will be at 80% when your volume is at 40% so you run out of room.
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    Quote Originally Posted by MacLeod View Post
    No amps have "head room". Different companies rate their amps differently. Pay attention to the THD number, this is kinda like an RPM gauge and shows you how hard the amp is being pushed at that rated number. So an amp that does 100 watts at .5% THD might do 130 at 1%.

    Headroom would be determined by gain settings. If your gain is set low, you'll have tons of headroom cause your volume knob will always be behind the amps input. If you have the gains too high, your amp will be at 80% when your volume is at 40% so you run out of room.
    Valid point about the THD%, and as for your second paragraph, that's why I always push people to put down an amp who's RMS meets the speakers peak. You never get close to an unclipped signal, which is rough on your speakers and your hearing
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    Why not run class A/B to the comps and class D to the subs.
    If you come to Canada, remember our bears like no foam lattes......thank you :D

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    D-class amps are notorious for what I call dirty sound.. I have neve used one as a main amp only for subwoofer duties..in to which they were first designed for.Ihave installed many different brands of D class amps. and I found that the Maphis amps are a pretty decent buy for a normal sub enclosure install for all out and out impossible loads tho the Cadence 110 watt D-class was a store favorite.. great power, fairly clean for its design and not to expensive..personally I like to use a/b amps to power everything ..I dont mind the extra power concerns when I know what im getting in return...
    Read thspecs,

    read the reviews, do the research but most importantly...Listen and make your own decisions.
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  17. #17

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    Default d-class

    Quote Originally Posted by Mahna Mahna View Post
    Why not run class A/B to the comps and class D to the subs.
    Your right thats the best way, and my headlights dont dim as bad when the sub moves far .

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    Quote Originally Posted by MacLeod View Post
    No amps have "head room". Different companies rate their amps differently. Pay attention to the THD number, this is kinda like an RPM gauge and shows you how hard the amp is being pushed at that rated number. So an amp that does 100 watts at .5% THD might do 130 at 1%.

    Headroom would be determined by gain settings. If your gain is set low, you'll have tons of headroom cause your volume knob will always be behind the amps input. If you have the gains too high, your amp will be at 80% when your volume is at 40% so you run out of room.
    Don't forget about slew rate. It lets you determine what the maximum input frequency applicable is so that the output isn't distorted. It's defined as the maximum rate of change of the output voltage for all possible input signals. So, essentially, the higher the number, the better. You want a high number so that you don't reach a signal clipping point where the amplifier cannot effectively amplify the signal. You then get those "non-linear effects" that usually kick on protection circuits where you're doing things like sending straight DC to the speakers or the signal clipping is so severe that the speaker just kicks out and strains without making any noise. You burn up voice coils and I've even seen cones explode and be ejected from the basket.

    Slew rate will tell you a great deal about the amplifier. You can see how "real" the rated power numbers are and whether they were fudging numbers on the THD rating to get a more attractive selling point.
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    So where do i find that slew rate?? Just looked thru PA1200.1's specs on Crutchfield - no mentioning of "slew rate"

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    Datasheets. Not everyone publishes them on ads or descriptions in retail stores. You usually have to go to the manufacturer's website or find their customer service number to have them send you the info.

    If you can't get a slew rate from the company, a damping factor value can suffice. Damping factor is essentially the ability of the amplifier to control unwanted driver movements near the resonant frequency of the speaker system. To be able to do this well, it needs a high slew rate because that's where the power to enact the control comes from. The slew rate is the maximum rate of change measured in volts per second. The damping factor isn't measured, it's derived as a ratio between source impedance and loudspeaker impedance. A high damping factor means the amplifier can exert a good deal of control over the resonances but to do that it needs to be able to respond quickly to changes and that is determined by the slew rate. A low slew rate usually makes for a low damping factor. The damping factor doesn't tell you as much as the slew rate would but you can get a good idea of what you're looking at.

    However, as we all know (or at least should know), voice coil impedance changes with temperature. So does the impedance of your wires. Impedance also changes with frequency. Because of this, the damping factor can change significantly throughout the performance of the loudspeaker. This makes it not really ideal for understanding the amplifier behaviors because it changes so much. Typically, the damping factor describes low-frequency performance. Like I said before though, resonances are usually at the lower end of the driver's frequency range where the most power is required to effect change on the speaker. Because you need all that power, you need a high response rate to compensate for not only the impedance changes but the resonances as well. So a high damping factor will usually equate with a high slew rate because of the power requirements needed to control the mass of speaker cone and overcome the stiffness of the surround to control the resonance movements.

    If you open the Owner's Manual here on the Polk site for the PA1200.1, you'll see that the damping factor for the amplifier is listed at 150. That is actually quite high. It's about as high as you'll see listed unless you go with something really esoteric. However, unless you are driving REALLY inefficient loads, anything above 150 is a moot point. To get to those numbers though, you need a high input (load) impedance and a low output (source) impedance. If you have such a disparity between the two, you likely have a high slew rate with a fairly moderate to low THD. The higher the damping factor number, the greater the difference between the two impedances. That usually means that the amplifier does not have to work real hard to handle the loads. This means less chance of distortion over the range of performance (THD), a better ability to handle impedance changes and a high rate of control (slew rate) over the driver movement.

    Of course, most of that is assumed but unless the company is faking numbers, you don't get such favorable results with inefficient amplification circuit designs. If they are faking numbers or at least fudging test parameters to achieve attractive numbers for marketing, it'll be readily apparent in a real world application.

    BTW, that's all a bit over-simplified. There's alot of math involved and it's difficult to go in to a forum. There are several sources on the Internet that can describe in detail the various subjects listed above and how they relate if you are so inclined. Even Wikipedia has some good write ups that are thorough enough and in plain English.
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    Quote Originally Posted by Jstas View Post
    BTW, that's all a bit over-simplified.
    yeeeeeeaaaaahhhhhhh........ LOL

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    Quote Originally Posted by Vital View Post
    yeeeeeeaaaaahhhhhhh........ LOL
    Well, if you already know then why'd you ask?
    You're just jealous 'cause the voices don't talk to you!

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    ^^^ lol that "yeeaaahhh..." was sarcastic. My brains boiled reading what you wrote lol.

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    Sound-quality of Class-D Amplifiers Less distortion than class AB ?

    A main disadvantage of class B is crossover distortion as discussed completely by Douglas Self in EWW.
    See also http://www.dself.dsl.pipex.com/

    In most high quality amplifiers this distortion is reduced by rising the bias current, making the amplifier operate in Class A at low power levels. This reduces the distortion at the zero-crossings but the problem is then shifted to a higher level where class B begins.

    Another distortion mechanism of class B is supply line pollution, When we look at the supply current during a sinusoid output signal, it looks like a single phase rectified sine with high harmonics generated at the sharp edges. At higher frequencies the PSU rejection ratio is poor resulting in highly non-linear modulation of the output-voltage. An power supply with zero output resistance at all audio frequencies will prevent this problem. In better Analog amplifiers the housings are filled with caps of 10,000 mF or more per channel to reduce the supply resistance. In class A operation there is no supply problem at all, except the huge energy account. The current drawn is only DC.

    Distortion mechanisms in class D :
    In a class D amplifier the distortion mechanisms, are complete different. Distortion at zero-crossings like in AB amplifiers does not occur.

    A similar but very complex distortion mechanism is caused by the dead time period between the switching periods of both transistors. When both output transistors are in off-state, the output voltage at the transistor-output is dependent of the current in the filter-coil, which is non-linear dependent of the momentary output-level, creating a voltage drop when the output-current reaches a certain level.

    By switching on the 2 transistors fast after each other, with a dead time of only nanoseconds, this distortion-mechanism is minimized. In the remaining dead-time, the momentary output voltage is determined by the charging of the parasitic output capacitors by the inductor current. A large parasitic output capacity smoothens this error voltage, reducing the distortion to only low harmonics.

    This distortion gets measurable (-100dB) when the output current is reaching the peak of the sawtooth-shape idle-current of the output-inductor. This current draws no power when the Q-factor of the output inductor is high. In our amplifier LPC1 this idle-current is 1/3 of the maximum output current (12 Amps) so the dead-time-distortion begins at 10 dB below maximum output. Using the high idle-current for charging the parasitic capacity will also reduce the switching losses.

    The dead time is accurately matched to the charging time of the parasitic output capacitors for minimizing distortion and switching losses.

    The supply line pollution has of a much more friendly behavior. Looking at the current drawn from the supply lines, its waveform has a low-frequency component, which is the square of the output signal. With a sinusoid as output signal, and a certain linear output resistance in the supply, a signal with the double frequency will be added to the supply voltage. In a PWM output stage with no feedback the output-signal will be multiplied with this supply voltage. A sinusoid output signal will be modulated by its square and thus resulting in pure third harmonic distortion.

    It can be easily calculated that an output stage without feedback driving a 4 Ohm load to 80% of the supply voltage (80V), (resulting in 128W) and powered by a poor supply with 0.1 Ohm will result in 1% D3 distortion. If the supply is only buffered with a capacitor of just 3300 mF and the output stage is fed back with a bandwidth-product of 100 kHz, this D3 is reduced to 0.005% (-86 dB) at all frequencies. However when the supply is only buffered with large caps, low-frequency signals can cause second order inter modulation at higher frequencies which is much higher than this calculated D3.

    In the LPC1, the supplyline intermodulation is cancelled completely by a patented circuit, making the amplifier open-loop gain fully independent of supply voltage, even at 20 kHz.

    Sound of THD
    The main explanation for the better sound-quality in this class-D amplifier is that the calculated and measured non-linear distortion mechanisms all result in distortion-components which increase proportional with the sound level. The relatively high THD-number (0.003% or 90 dB at 1kHz, 400W) comprises most low (3rth and 5th) harmonics.

    This distortion is masked by the non-linear distortion and compression of most ears and loudspeakers. In contrast, the harmonics caused by crossover in class AB do peak at low output levels, and have a wider spectrum, making the same THD-number much more audible.

    Output impedance
    A second disadvantage of a switching amplifier is its complex output impedance caused by the output filter.
    The output voltage gain is frequency independent (within 0.1 dB to 40 kHz) when the amplifier is loaded with 2 Ohms at all frequencies. But at other loads the output impedance will affect the frequency response.
    This effect is minimized by making the inductors in the output filter as small as possible (6 + 2 microH when designed for 2 Ohm).

    The poles and zeros of the filter impedance are outside the audioband, and the output inductance causes only a rise or fall of the frequency response (until +2 or -1 dB at 20 kHz) when loaded with 4 or 1 Ohm instead of 2 Ohm. This can be equalized easily. The inductance of loudspeaker cables (especially the expensive ones) is in the same order of magnitude (but not compensated) as the (8 uH) inductance of the filter. For a flat filter response, a constant speaker impedance is recommended.

    A class D amplifier with extra feedback from the output of the filter, reducing the output impedance, is in development.


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