A common problem of Class D amp is the switching noise it generates which can cause mid and high frequency sounded edgy and dry. But its high efficiency and cool running is perfect for subs. IMHO.
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what they said.
the JL Audio line of subs uses class D. i've owned a pair of f113's.
my Evolution Acoustics MM3 speakers have integral powered subwoofers which use the 1000 watt ICE modules.
as mentioned above, ruthless neutrality (or switching noise?) is a detriment to music in the mids and highs, but a real advantage in the bass. Class D amps are small, efficient and don't get hot. they are also relatively cheap to make.
conventional amplifier circutry has problems with linearity in the bass; not so Class D in my experience.
You should check the damping factor of the class D amp you are considering for driving subwoofers. If damping factor is high--often in the 1k range--you should have no problem. . . If instead the damping factor were low, you may discover control problems, like with any low damping factor amp of any other technology. As for mids and treble sounding foreshortened or noisy in a switching amp. . . like with amps of any other underlying technology, it depends on the individual amp implementation. E.g. I can't perceive any obvious switching noise nor foreshortened mids/treble from my JRDG 312
Very interesting posts!
Most, if not all, class D amps put out a lot of noise starting around 15 to 20 KHz and climbs to surprisingly high levels in the ultrasonic and up into the RF range.
This noise can be filtered out if the amp is designed into a dedicated speaker. But in the case of a free standing amp, such as the unit I have, there is little that can be done about it since the designer has no idea of what speaker will be connected to it. The impedance curve of the speaker has to be taken into account when the filter is designed and therein lies the problem.
Eldartford does have a good idea to see if the Class D amp is messing with the upper ranges in the main speakers. I will have to try this now that I am curious about it. But as Sidssp pointed out, my question was more oriented toward how the Class D amp sounded in the sub bass, where it is driving the speaker.
Take a look at this datasheet for a Class D amp. Although this is a rather inexpensive Class D chip, you can get an idea of the noise output in the ultrasonic and RF range. Go to page 8 and look at the middle three graphs. Note how much noise is in the inband and outband graphs. This will indeed affect the sound. Just understand that the audiophile gear we buy would have better noise characteristics than this particular chip. Also, as I mentioned above, dedicated amp/speaker combos would have a filter to eliminate this. But this datasheet does give you an idea of the noise from a Class D.
Anyway, I starting to sidetrack. What I noticed about my system here is that the bass is not quite as lively sounding; rather it strikes me as a bit on the dead side. If I had to guess, the somewhat dead sound is due to the noise output.
Before I installed the 450W Marantz unit, I had four Amber 70's driving the four subs and it sounded much more musical. The problem was the 70W Amber ran out of voltage on the louder passages and clipped. Hence my purchase of the Class D - actually, I hadn't planned on buying an amp at the time but the price was too good to pass up! With 450W into 8 Ohms it doesn't clip now, that is for sure!
However, it gets worse.
Both of my tuners, the Amber/Rotel digital and the older Sansui TU-777 are both unusable when the Class D amp is on. There is so much static and interference, the system is simply not listenable. I have tried a lot so far to fix it but nothing has had much of an effect. Here is a brief list: separate AC line, huge ferrites on AC line, rca inputs, and speaker outputs, moving all the cables from the amp well away from everything else, etc. So far, nothing has helped. I did the same thing to the FM tuners, too.
My next idea is a large attic mounted directional antenna with a booster on it. I am hoping the larger signal working along with the internal squelch circuit, might block the noise. After that, my next trick is installing a large ground rod and running #6 copper ground wire to the chassis to see if that helps. I might try grounding the FM chassis, too.
I suppose I could just go out and buy four Mark Levinson, Krell, or Parasound monoblocks but let's keep it real and not dwell in fantasy land.
Anyone have any other suggestions?
Spatialking - You stated that many if not all class D amp create noise starting at 15kHz but even curves that you refer to on page 8 of Maxim datasheet shows no noise (above -100dB) up to 300kHz (carrier frequency). This noise is filtered usually with zobel network and only about 1% of noise gets out. At this frequency (300kHz) speaker cables have to be 820 ft long to create 1/4 wave antenna.
My Rowland class D amp is placed directly under TV and even with weak analog signal I cannot detect if amp is ON or OFF (not even slightest difference in noise).
Tweeters are dead quiet when I place my ear directly on it. Performance is amazing - much cleaner and liquid than class AB amp I had before.
All amps produce switching noise. Traditional amps drain current from mains in very short spikes of high amplitude repeated 120Hz.
Could you please provide example of common class D amp (Icepower, Hypex etc.) that produces switching noise at 15kHz?
Kijanki - switching noise is typically defined as clock noise in this digital world we live in. Although it is technically correct to say "switching noise" when a diode turns on and off, that noise is insignificant to clock noise on the output of a Class D amp. It is incorrect to say a Class AB linear output stage produce switching noise when moving from positive to negative or back. If it produced switching noise, it wouldn't be linear by definition.
I will have to check to see what Class D noise curves I have left over from when I worked at Maxim. I know I have some white papers showing some noise at 15 KHz.
It really is amazing how much noise there is in the output of a Class D amp. Unless you have a filter on the output, you will have noise, there is no question of it. The only question is at what frequency ranges the noise will peak.
The filters in question here are hardly zorbel networks, although they would help a bit. The filters i have seen in use are usually 3 or 4 poles and are rather aggressive, high Q passive networks.
Depending on the amp, you may or may not have audible noise at 15K Hz. As I mentioned above, comparing the inexpensive Maxim chip to an audiophile piece of gear such as your Rowland is just not comparing apples to apples. Frankly, if your Rowland produced audible switching noise at 15KHz, I would send it in for repair. Just understand that noise at 60 db down will impact the sound, you just won't hear it as noise. My personal belief, based on designing a lot of audio amplifiers, is anything above 140 dBV inside a linear amplifier with some loop feedback will impact the sound in a negative way to some degree.
You don't need a quarter wave antenna to jam the airwaves so that FM broadcast won't get through. I suspect the noise problem I have is more harmonically related than fundamental related. A 1/4 wave antenna at FM frequencies is on the order of a few feet, depending on the propagation velocity of the wire.
Also, my Class D amp is only 10 feet from the tuner and maybe 3 feet from the antenna. The FM broadcast antenna is miles from here. Granted, the broadcast antenna is in kilowatts and the amp is not, but the energy from both decreases as a square of the distance. The amp may not produce as much energy as the broadcast antenna, but here in my living room I wouldn't bet any money on which produced more signal in the antenna.
I don't know if you live near me but a few seconds of having this Class D amp powered on with FM will convince you there is a serious radiated or perhaps conducted noise problem here. As I write this, I have the FM radio on, but the subs are not powered on!
What I do find really encouraging about all of this are the number of folks who are really happy with their Class D amps. If everyone here was telling me I have a problem simply because I was dumb enough to buy a Class D amp, I wouldn't bother to try and fix this problem.
Just a thought but -- have you tried a different tuner? I used the Sangean HD-Radio tuner with three class D amps in very close proximity and had no problems picking up even very weak stations. In fact, if you want to try it, I'll sell you mine super cheap -- space considerations and a system relocation forced me to switch to a Pro-Ject tuner box (whichb also works fine in reasonbly close proximity to a different set of Class D amps.
Spatialking - yes your FM antenna is miles away but the output LC filter of class D amp is set to about 60kHz and at, for instance, 60MHz has very very high rejection.
(and 60MHz harmonic of 60kHz is a very small fraction to start with).
Also FM transmitter, as you mentioned, has kilowatts and not watts.
Carrier frequency, or rather 1% of it that gets out, is not audible (unless one can hear 500kHz) and cannot even create intermodulation on nonlinearities on the tweeter since its membrane won't move at 500kHz at all.
Jeff Rowland made many preamps using batteries in power supply. One of his newest creations (with extremely fast op-amps) Capri - praised for great sweet airy sound has switching power supply. High frequency noise is easy to filter out. The noise I was talking about was not the output noise in class AB amp but power supply current spikes it creates (not so easy to filter out).
It is possible that your class D amp is simply faulty or poorly designed.
It is amazing to me that many people (not you) wouldn't consider class D even for subwoofer but never heard one.
If class D is not good enough even for subwoofer please read fragment of the review of the Cabasse La Sphere 5200W (fifty two hundred watts) Icepower class D system by John Atkinson (Stereophile):
"In terms of organizational skills, timing and phase coherence, and timbral and textural accuracy, Cabasse's La Sphère system sets new sonic standards. Its reproduction of the piano and the human voice is light-years ahead of anything else in my experience. Its ability to produce solid, three-dimensional images on a stable, remarkably well-organized soundstage also beats anything I have ever experienced anywhere, and by a considerable margin. And in terms of textural solidity, harmonic structure, overall control, and low-end extension, its bass performance is similarly unprecedented."
Its been said many times before...its not the class of the amp, its the implementation. We shouldn't compare cheap SS designs with the best SS, nor cheap tube designs with the best, nor cheap early renditions of Class D with the best. Class D was known for its radio interference in its early days. New designs like my Bel Canto are light-years ahead in design. As time marches on, amps designs will continue to improve. Tube has the longest history, SS next, and now Class D. No doubt there will be superb designs of Class D, and new classes of amps in the future, as long as people will buy them. As ong as the amps are working for you, be content. If you upgrade to newer and costlier designs you will hear the difference.
Thank you Grisham, you beat me to the punch! In answer to Bob_reynolds, there are some problems in citing the D-100 review to prove that switching amps are inherently problematic.
1. The review is of a moderately priced amplifier deliberately engineered to meet an affordable price point. D-100 was not intended to redefine the absolute state of the art in monoblock amplification such as Spectron monoblocks, JRDG 312 and 301, Mark levinson No. 54 (hope I got this model correctly).
2. The article is obsolete. It was published in August 2005, probably written about 6 months earlier. . . essentially it is 4 years old, which is a lifetime ago when it comes to the significant strides that the rapidly evolving class D designs are making.
3. From a symbolic logic point of view, the induction step according to which 1 tested amp of a given class having been found to have a flaw, all amps of the same class bear of necessity the same flaw is, . . well. . . flawed itself.
Guido - Issue of the noise came in Stereophile review of Channel Island D100 (Hypex) only because test instruments listen to much wider frequency range than necessary. Yes - all class D amps produce some noise but it is in hundreds of kilohertz - non-audible and not in the FM or TV bandwidth. Any amplifier produces switching noise - even class A or tubes. It comes from power supply (sharp current spikes repeated 120Hz).
As for D100 - it is very good amp. Stereophile says that is "going head to head with an amp as good as the Coda S5". (good class A amp).
Reading your post one would think that D100 is bad sounding or very noisy.
Ah yes, I do remember the discussion. . . tell the truth, I happen to kind of agree with the raw findings of the panel when they reviewed individual amps. . . what I have always problems with is the infimous application of the generalizing induction step. It is worth observing that the amps TAS examined were relatively early products created specifically to meet a particular price point. Most of those products have since then been replaced or enhanced. The Spectron for example, has been significantly enhanced since then. . . recent Spectron entries cost upwards of $22K per monoblock pair with performances to match. The Rowland 201 monoblocks conversely are still current production. They were, and still are the entry level monoblocks of the JRDG product tear and are in consequence designed to meet their price point. JRDG has amps costing upwards of $30K, also with performance to match their price points.
Let us ask ourselves the following: would it be particularly meaningful to promulgate blanket condamnations of the current state of the art in tube amplification, including such extremely high end devices as ARC Reference 610T or VTL sigfried, by generalizing on some supposed shortcomings discovered several years ago in some now obsolete entry level designs?
I have a Mcintosh pre in front of a Mc power amp (300x2)driving the front and a Cerwin Vega (2800x1)driving 2-Electro Voice EVX 180's. In my apinion,you do'nt need a reel good amp for bass. The bass is tight hard hitting and the Mc run very cool because it's not driving any bass.By the way,I use a E.V. 2 way active X-over that has a sub out.I bought the class H amp new for around $450.
It costs a lot more to have the Mc serviced and I bet I won't have to have the Mc serviced for a long time because it's not driving the bass. If I blow the C.V. it's no big deal. Just buy a new one. Take care,Bill
Kijanki: Sometimes I write in the manner I speak rather than write in a more coherent manner. As an Electrical Engineer, I know the difference between Watts and Kilowatts. I apologize for not being more clear. Frankly, I wish the station broadcast in the MegaWatt range, at least the signal would be a lot stronger here. My favorite Jazz station is privately funded - their broadcast is so limited I can only listen to it clearly in Silicon Valley. East of the hills in the East Bay, their signal is very limited. Sigh...
High Frequency noise is "easy" to filter out within a band of frequencies. However, as the bandwidth increases, filters become more difficult to design and thus noise become more difficult to eliminate. When you consider you also have to filter electromagnetic noise as well as electrostatic and conducted, and the fact our noise spectrum now extends into the GHz range, it is no longer a trivial task.
Do understand that any noise spikes created by the diodes in a linear power supply is insignificant in comparison to the noise created by diodes and components in a switching power supply or class D design. This doesn't mean anything with a switching power supply is bad, but it does mean more engineering work has to be done to eliminate the resultant noise that comes along with it. Also note that this diode "switching noise" in a linear amplifier is actually the transformer radiating, not the diode. But, again, this noise is insignificant in comparison to the noise created by a switching power supply of comparable quality.
Class D amps grossly violate the KISS principal, but it is being widely embraced because most of us who have a multichannel 300W+ per channel Class D amps couldn't afford it if it was Class AB and certainly couldn't afford to operate it, much less buy it, if it was pure Class A. This is in addition to the fact that Class D makes higher power, battery operated personal stereos possible.
Given a fixed amount of money to spend, choosing a Class D amp for the midrange and upper frequencies would be my last choice over a good tube or Class AB solid state design. I do believe it is much more difficult to design an equivalent sounding Class D amp to a Class AB design.
Tgrisham: I agree with you on implementation. This Marantz amp I have had a sticker price in the 2000+ dollar range. I don't remember exactly, I would have to look at the receipt if I still have it, I am thinking it was around 2400. I bought it at 60% off due to store closure and the fact it was only four channels and not six made it hard to sell. Clearly, it isn't a cheap design - even though it is Class D it still weighs over 60 pounds. It is possible that I have a bad amplifier but I am more inclined to believe I have an implementation problem of some sort here at the house. A Class D amplifier design engineer I know now works at National Semiconductor, I think I will look him up tomorrow and discuss this noise problem with him.
Bill: I agree, the use of an amplifier as a subwoofer only makes the choice of amps much more easy. For one thing, it has only a very limited range of frequencies to reproduce and any nonlinearites created by producing 80% of the power in music is not fed to the upper octaves where your ear is most sensitive.
In addition, designing a subwoofer only amplifier is easier in that more feedback can be used without the resultant hardness through the midrange. The additional feedback increases the damping factor which usually improves the bass and the limited frequency range of the bass frequencies means upper bandwidth can be sacrificed for the increase in feedback to maintain stability.
Unfortunately, history has shown it is more difficult to sell a standalone, subwoofer only amplifier. Although once installed in the subwoofer cabinet, they seem to be selling quite well!
Spatialking - Noise in linear power supply comes from the fact that capacitors are recharged only in narrow spikes. Width of the current spikes, often called "conduction angle" can be found by analyzing output impedance of transformer and ESR of capacitors. Guy named Schaffer made diagram (it was long time ago - I'm not sure of the spelling). These spikes can be very narrow and heat-up the core of transformer by high frequency content and windings by big rms value (and you'll see them in power cord). Transformers in linear supply are therefore designed for over 150% of needed power. Unfortunately nothing will remove noise they produce. People call it linear but it is in fact SMPS operating at 120Hz. Traditional transformer is also very ineffective since 2" toroidal transformer at 60kHz can carry the same power as huge 8" toroid at 60Hz.
Switching power supplies are wonderful since they work at non-audible frequencies (easy to filter out), don't radiate since frequency is too low and the only questionable might be capacitive coupling that is easily handled by shielding. Also, they can be designed extremely quiet (that's why Jeff Rowland used it in Capri preamp), and are line and load regulated.
Linear power supply is a dinosaur because to provide any temporary regulation you have to put a lot of capacitance and this brings inductance into the picture (unless you use expensive caps like slit-foil). Inductance slows response and putting film or ceramic caps in parallel creates parallel resonant circuit that rings (and this circuit is in series with the speaker). Response of SMPS is very good and you can find in reviews of Bel Canto s300 or REF1000 that they keep composure and dynamics even at very high levels.
Class D is not so difficult to filter out. Zobel network filter according to my estimates leaves only about 1% of the switching frequency (about 0.5MHz) on the speaker cables and almost nothing of higher harmonics. At this frequency speaker cable has to be few hundred feet long to be 1/4 wave antenna and going below 1/8 wave will produce extremely low radiation (antenna becomes very poor). I cannot detect on my TV in any mode and even with very weak signal any difference in noise while switching my 2x200W class D that is directly (less than foot) under TV. TV itself has most likely switching power supply as well.
I cannot say how good is class D in comparison to great tube or AB amp but I know that is very good for the money.
I have one of the cheapest class D amps and it is way better than class AB I had before.
What class D amps did you audition?
Spatialking - One more thing. Class AB even at 2x300W is not expensive to operate since average music power is only in order of few percent of maximum power (Class A is a real problem though). Operating cost was not a reason for class D in audio. Class D doesn't produce TIM distortions and in effect higher order odd harmonics. Time used insted of voltage doesn't have big nonlinearities typical for class AB output transistors. Class AB amp has gain before feedback of many thousands to make low THD and IMD (class A has at least 10x less gain) but tends to produce TIM ("transistorish sound").
First, let me state I "fixed" the radiated noise from the Class D amplifier interfering with the FM radio. I bought a new antenna and positioned it 20 feet away from the Class D amplifier. Now, there is no audible noise in the FM. I also found that the antenna I used had more of an effect on sound quality than the FM tuner!
Using the standard, cheap, 300 Ohm lead dipole that comes with every FM tuner you buy could produce either good sound or poor sound, depending on how you orient and where place it. Switching to a directional, high gain, wide bandwidth FM antenna on a rotor could make the sound quality better or worse than the cheap dipole, depending on where it is placed and its orientation. I think the next step is to buy a better directional antenna and install it in the attic with a rotor.
There is no question that both of my Class D amps radiate like the dickens and the pickup is through the FM front end. Adding massive EMI cable ferrite assemblies on the coax, line cord, and speaker wires did little to solve the noise problem.
Kijanki: What you wrote is not exactly correct nor complete. The conduction current spikes you mention do exist in the manner you describe, however your analysis is not complete.
First, the conduction spikes caused by diode action you describe are well known and are published in every engineering textbook that discusses converting AC Mains power to unregulated DC voltage. I am pretty certain the first engineer to build a circuit which did this was in the mid or early 1800's, long before DeForrest invented the triode vacuum tube in 1906, I think it was.
Don't think for an instant that switching noise spikes don't exist in a SMPS, they do and are larger in magnitude than in a linear PS. They are, however, quite different in nature in a SMPS than in a linear PS. In addition to this, you also have noise from the clock frequency to deal with. There are SMPS out there with clock frequencies at 1MHz and higher, although I believe most SMPS run in the 100KHz-ish range.
The method to eliminate radiated noise caused by the current spikes in a transformer, whether SMP or linear power, are the same and is not difficult nor impossible to do. It does add cost however, and that is the key.
In addition, the frequency of operation also comes into play: the higher the frequency the smaller the size of transformer for a given power output. However, higher frequency does not mean lower radiated noise. What it does mean is that the transformer is smaller and thus the shielding can be smaller, meaning lower cost. SMPS's are also significantly less expensive than linear power supplies for a given power. They are also much more complex. Note that the stability requirements for a SMPS are the same as for a linear, regulated supply as both involve loop feedback.
The first approach to remove radiated transformer noise, which is probably the most common, is to design in a Faraday shield in the transformer. A transformer using a torrid design is a better and more expensive approach.
Second, a Faraday can could be placed around the transformer and depending on how much money you want to throw at it, you can make it out of iron, copper, iron and copper, or mu-metal.
Third, you can remove the transformer from the chassis and place it in another chassis several feet away from the sensitive electronics. Certainly this has been done numerous times in high end audio equipment. Fourth, you can use a combination of these approaches, not to mention this is not an exhaustive list. For example, I did not mention the quality of the transformer design.
If you want to remove the current spikes caused by the full wave diode bridge circuit in front of a huge capacitive input filter for a large power amplifier, the best way is to eliminate the capacitor based filter which causes the current pulses.
Instead, design a PI based filter where the series inductor is designed to handle the worst case current the amplifier is expected to deliver. In this case, the current spikes which occur become nothing more than 60 Hz sine waves where the magnitude of the current is about what the power supply is delivering.
Don't misunderstand me, this is still an unregulated raw supply. To complete regulation, you still have to add a linear regulator on the output, which is effectively adding another amplifier in series with the signal amplifier. A SMPS does exactly this, as the SMPS is effectively another amplifier whose output is DC.
I am sure you can see that a SMPS power supply is less expensive than the standard regulation circuit just described. Just as there is no question a SMPS is less expensive, there is also no question a SMPS is more noisy and that noise has to be dealt with.
Note one can use all the noise killing techniques described above, including putting the PS in another chassis, and then using a regulated SMPS as well to reduces the cost over a linear supply.
This is indeed a less expensive approach, but it is still more expensive than using a full wave, capacitive based, raw supply which is why this is still the most common approach in linear power amplifiers. Since the amplifier has inherent power supply noise rejection, and the 120 Hz ripple left over in the output voltage is well within the feedback loop bandwidth, I am sure you can see why this is such a popular approach.
There is no question, at least in my mind, that there are better sounding approaches to power supply design in power amplifiers than an unregulated raw supply, it doesn't change the fact it is still a popular approach.
Kijanki, I forgot to mention that I agree with your statement that Class AB is not expensive to operate, I disagree with your statement that distortion mechanisms is the reason for Class D in audio today.
The reason Class D is in audio today is the lower cost to produce a given power output and efficiency of operation. Let me discuss these separately, since they apply to different markets.
A Class AB, two channel, 200 or 300 Watt power amplifier is probably affordable by most audiophiles unless one considers the more exotic and expensive designs. Certainly, I don't need to mention the more expensive brand names here. However, given the cost of the more mainstream 200W stereo amplifiers, it should be obvious that a 200W Class D amplifier is less expensive for a consumer to buy than the same power in a Class AB amplifier.
Class D has really come into its own due to the proliferation of home theater systems where one needs 6 or more channels of operation, the cost of these systems are much lower using a Class D approach. In addition, the proliferation of portable sound systems demand the efficiency of Class D operation since they have to operate by battery power and conserving battery power is everything in a battery based design. Battery powered personal sound players is obviously a big market as are laptops computers which also have to produce sound as well.
As pointed out elsewhere in this thread by knowledgeable folks, implementation of a technology is more significant than the technology itself. Granted, a Class AB design has some inherent distortion mechanisms eliminated by a Class A design, that doesn't mean a Class A design sounds better than a Class AB design. Whether it does or does not is dependent on the trade offs chosen by the design engineer and the manufacturing techniques and quality.
The same applies to a Class D design. I disagree with your statement that a Class D amplifier has inherently less TIM distortion than Class AB design; whether it does or does not is irrelevant. Frankly it adds new distortion mechanisms that do not exist in a Class AB design. Given the increase in complexity of a Class D design and circuit, implementation is substantially more significant to the quality of the output signal.
This reminds me of CD player manufacturers which still specify wow and flutter as a distortion mechanism. It is obviously designed out in a CD player but it is rare to see a jitter specification in inexpensive CD players. Jitter is a new distortion mechanism which did not exist in a LPs.
Spatialking - It is not so bad with transformer radiated noise - toroid should solve it. It has 10x less radiated noise than standard transformer and my Benchmark DAC1 has measured 140dB S/N with power supply toroid next to circuitry and without any shielding. I was talking about current spikes coming thru power cord of linear supply.
Just opposite to good SMPS that switches at zero voltage - zero current, linear power supply switches at maximum voltage.
As I said before linear power supply is in reality 120Hz SMPS where width of current spikes from mains depends on the load.
Yes, linear power supply can be filtered out with pi filters as well as regulation can be added but they don't do it. Pi filter costs and inductor would have to be huge while regulation will add enormous amount of the heat (and therefore heatsinks) since it needs to cover typical 90-132V range. I don't know of any audio amps that have regulated linear power supply - but also I don't have a lot of experience in audio gear.
Jeff Rowland used SMPS in his CAPRI preamp not because of lower cost but because of lower noise. Linear power supply - even regulated would be very inexpensive for the power needed by preamp - SMPS would not give him any savings.
Noise from SMPS is, as you stated, usually around 100kHz (but can be even 1MHz for lower efficiency/lower power demand). This frequency is non-audible and its harmonics would be perfectly filtered-out before we get to your FM radio frequency range. I agree that SMPS is often used to save cost with undersized transformer and poor filtering (computers) but it doesn't have to be. Everything is in the hands of designer.
My computer, monitor, TV, amplifier, DVD player, electric shaver, cordless phone, Cell phone, cell phone charger and who knows what else in my home - ALL have SMPS power supplies. I'm not worrying about noise produced by my class D amp because it is well below FCC requirements.
"There is no question, at least in my mind, that there are better sounding approaches to power supply design in power amplifiers than an unregulated raw supply, it doesn't change the fact it is still a popular approach."
Spatialking, Higher end class D amplifiers use a high degree of SMPS regulation. E.g. JRDG 300 series amps: 301, 302, 304, 312, as well as Bel Canto Ref Mk.2 series. JRDG also makes use of active PFC in its pre power supply circuits. Switching frequency of JRDG 302 SMPS is in the 1Mhz range. In my experience, a discussion of unregulated SMPS implementation is not applicable to newer design amps ranging in cost from $5K to $50K.
Before you expend any more energy attempting to prove the supposed inherent musical inferiority of class D designs to more traditional ones on theoretical generalizations, you may want to let your ears do the walking. Consider granting some in depth listening to the recent statement level creations of leading class D amplifier designers. If after that you still did not like them, you would at least anchor your preference on applicable personal experience. Guido
Kijanki, I don't believe any SMPS is quieter than a linear regulated supply regardless of what the diodes are doing in a linear PS. Sure you can design SMPS to switch on and off at zero crossings but you still have to deal with clock noise. If a SMPS is low noise, it is only because some design engineer somewhere worked pretty hard at getting the noise out.
There are cases where linear regulators are used after SMPS regulation simply to eliminate the SM noise. I think Maxim has a patent on this and they do use this approach in many of their sensitive chips. I know, I worked there as an apps engineer for a while.
Also, please note that any noise, at any frequency, injected in the bandwidth of the amplifier has a negative impact on the sound quality. This is especially true at higher frequencies where PSRR of the amplifier drops off.
The reason for this is that any noise injects additional energy into the bandwidth of the amplifier. Sure, you may not hear it as "noise" but any increase in energy within the bandwidth of the amplifier will sound different. This is the basis Nyquist theory and all digital audio: a given bandwidth and given energy level sounds the same. Change either one and the sound changes.
Again, as I have stated at least three times now, just using a SMPS, or a Class D amplifier for that matter, doesn't mean the sound is worse than an Class AB design, it could be substantially better. It all depends on the trade offs made by the design engineer and how it was manufactured.
Guido: I stated above that I believe the sound of my bass is "a bit dead and not overly lively". I based this on listening to it, not from some datasheet or preconceived made up opinions about Class D amplifiers. I did not state that all Class D amplifiers produce bass that is dead or not overly lively. I did state that this is what I hear in my system and it is caused by my Class D amplifier. I was curious to see if anyone else had experienced the same sonic effects which I have.
Let me put it another way, approximately 1000 folks have looked at this thread. If say 30 to 40% of them stated something like "Oh, heck I have the same problem with my Class D" I would be inclined to find an engineering reason for it. This has not happened. Whatever I am experiencing here seems to be more related to my own Class D amplifier.
If I felt that Class D amplifiers were bad from bias, I wouldn't have spent a grand on Class D amplifier in the first place! I could have continued using the two Amber 70's I had. Actually, the only complaint I had about the 70's is the fact they only produce 70 watts. This is not a lot of power and I can clip them if I was not careful on the volume control. Otherwise, they sounded perfectly fine as bass amps. My subs are nominally 6 Ohms and the Amber's have plenty of current to drive 6 Ohms. The problem is they were running out of voltage, not current. A well designed amplifier should run out of voltage when they clip, well designed amps should not run out of current.
These aren't theoretical generalizations I am making up. If any Class D amplifier is going to have less radiated or conducted noise than a Class AB, it is because the design engineer made it happen because Class D designs have inherent noise that Class AB amps don't have. That is a fact of life, just as tubes have filaments, mosfets are voltage based devices, and transistors are current based devices.
I will admit that I am conservative when it comes to making changes in my stereo - This is the reason I have a Class D amp for the subs and I haven't sold my Premier Five CJs on the upper octaves. I could have sold the CJ's and ran the entire system off this monster Class D amplifier. I didn't do it, I wanted to see how it worked on the subs.
Please scroll up and read what I wrote about radiated noise from my Class D amplifier causing FM interference. If it was conducted noise, moving the antenna would not have any effect. But the fact that I moved the antenna and eliminated the interference proves the noise is radiated. Also, simply turning the Class D amplifier off eliminated the noise also proves my Class D amplifier is the source of the noise. If anyone still believes this noise is not from the Class D amplifier, they will simply have to stop by for a visit.
Again, let me state one more time simply using a Class D amplifier does not mean your system will sound worse than a Class AB or Class A or even a tube amplifier. It does mean that if you don't have a noise problem then the design engineer who designed it dealt with the noise problem. Whoever was the design engineer on my Class D amplifier did not do enough homework or I would not have had the interference problem.
Spatialking - As far as I know Nyquist and Shannon were describing sampled systems while class D is analog. Adding high frequency noise is often practiced (for instance in digital photography) to increase resolution. In image processing it is called dithering and is also used in audio processing.
I mentioned many times before, that noise is always produced - only high frequency is much easier to filter than 120Hz spikes (that carry a lot of high frequency energy) and that was main reason for Jeff Rowland Capri's SMPS.
I don't think I understand your statement "If it was conducted noise, moving the antenna would not have any effect" If you move antenna away and it stopped it was most likely conducted (capacitive) and not radiated (electromagnetic) noise.
At around 100MHz you're at such high harmonics of 0.5MHz carrier (Icepower) that there is almost no energy in harmonics to start with and even single capacitor would clean it (Icepower has second order filter).
I've read pretty much all posts on this forum (and others) regarding class D. 90% of people who dislike class D never heard one. Reading your original post I had impression that you don't even consider it for subwoofer much less for the main amp while according to all editorial reviews I've read bass is exceptional in class D.
(Just go back to my quote in previous post of John Atkinsons La Sphere system with 5200 watt Icepower system.)
At this point I'm not sure if you don't like it because of EMI, principle of operation (PWM) or the sound.
I don't know what Marantz screw-up in your amp (or what is wrong with your tuner/antenna combo)but mine is exactly under TV and has no detectable effect (speaker cables lying next to antenna cables).
If you believe that high frequency noise will affect audible band then go to Icepower 1000ASP datasheet and check FFT of its idle noise 0-20kHz - it is below -140dB (it should affect itself but doesn't). Also it has incredible IMD=0.002% and THD=0.007%. How many amps can output 100mW-1000W at 10Hz-20kHz with only 0.2% THD? For your subwoofer application DF=4000 should not be too bad as well as ability to output 40A for over 1 second.
As for disliking principle of operation (PWM) sigma-delta DACs, SACD and DSD studio recordings are doing exactly the same thing.
I can point you to review in Audioasylum where one guy bought Icepower amp to drive his rear spekers and after listening to it got rid of his main tube amp replacing it with Icepower. If you find Icepower sound not to your liking try Kharma or hundred other companies that produce class D audio amps.
It is entirely possible that you have better ears than mine or even more experience than John Atkinson (Stereophile) but if you just simply don't like the sound then don't speak poorly about whole class of amps that is not better or worse than other classes of amps and for the value are probably the best.
If you look into Icepower datasheet you'll find following statement:
EMI conforms to: EN55103-1
FCC part 15b Class A
And don't worry about SMPS in your TV (about 200W) since it follows the same standards.
You said that class D noise is inherent and if it's not outside it means that designer had to take care of it. First of all - I pointed that switching noise in very high current spikes is inherent to any linear supply and second I could make similar statement of tube amps - "they have inherent dangerous high voltage and if it's not on the outside it is because of the designer (transformer). It always is - don't analyze and just find better one than Marantz.
Dont know if this is applicable or not,used on 2 way legacy speakers,sure the bass went deep,but it wasn't natural,and it wasn't any better then what comes out of my counterpoint,the counterpoint shows its bass entirely with whats on the recording,if its light on the recording that's what comes out if its good on the recording that's what comes out,class d seems to really bring out more then really whats on the recording,overemphasizes if anything.
Kijanki: Actually, a Class D amplifier uses a digital technique to reproduce the sound. The amp is actually a Pulse Width Modulator with a power output. Envision a one bit DAC reproducing the sound and you have an idea of what is going on in a Class D. Technically, it is incorrect to say it is a digital amplifier, the difference is described in the papers below. But do understand a Class D amplifier is certainly not a linear amplifier!
See John Guy's paper at http://www.national.com/vcm/NSC_Content/Files/en_US/Audio/ClassDAmplifierFAQ.pdf John is a very knowledgeable fellow, I worked with him at Maxim. Believe me when I say he knows Class D amps! The paper pretty well describes the Class D noise on the outputs.
John also published another paper in Audio Design Line which describes how a Class D amplifier works. I think you can get this magazine emailed to you directly if you are interested - I am not sure if you have to be an engineer or not to get it. Anyway, check out the paper at http://www.audiodesignline.com/howto/177102531;jsessionid=CP1YPZLBM2M5AQSNDLRSKH0CJUNN2JVN This is one of the best papers I have seen on how a Class D amplifier works.
It helps to know some algebra when you read these papers, as well as know a little bit about basic electronics. Otherwise, they are a good read.
It is incorrect to say I don't like my Class D amplifier; actually I have no plans to replace it. In fact, scroll up a ways and note what I said about listening to it with a CD as a source last week! That sound and bass was excellent! What I don't like is the radiated noise from the unit.
Let me explain the difference between conducted and radiated. Conducted noise is conducted along the wires, say the line cord, RCA cables, or speaker wires. Radiated means the noise is traveling through the air, much like a radio broadcast. If the noise is conducted, it will disappear when you unplug the offending wire or at least diminish when you put some ferrite suppression on it. If the noise is radiated, then simply moving the affected gear farther away from the noise source will reduce or eliminate it since radiated energy decreases as a square of the distance.
Note that sometimes it is difficult to determine if it is radiated or conducted. For example, if the noise was conducted from the AC power cord, unplugging it would also kill the unit. The only way to find out if it is conducted from the power cord in this case is to swap out power cords. It is further complicated by the fact the noise can be conducted out of the chassis by a cable and then radiated from there.
The FCC Class A you mention above is required for everything that is sold which has a clock in it above 10 KHz, I believe. The Class A or Class B spec dictates how much noise is allowed to pass, per FCC. Class A is allows ~10dB more noise in selected frequencies and is normally used for industrial equipment. Class B is normally used for consumer goods, such as radios, TVs, or stereos with computer chips in them. Class B is significantly more strict with respect to radiated and conducted noise. Actually, I am a bit surprised to see audiophile grade gear sold with a Class A level, but the intended application is what normally dictates the A or B designation, not who buys it.
Also, just because the frequency goes up doesn't mean the harmonics diminish. Once you are above 1 to 10 MHz or so, the phase-coherent relationship outside the chassis dictate how significant the emissions are. I have worked in EMI suppression before and it is a common mistake to assume a 2 MHz clock won't have significant or fail Class B emissions at 800 MHz, but don't count on it. I have seen units fail at those frequencies with a clock in the 2 MHz region. FCC requires testing up to 1GHz and sometimes higher just for this reason.
Also note when I say bandwidth, I don't mean the audible bandwidth at 20 KHz, I mean the bandwidth of the amplifier. If a given amp has a bandwidth of 60 KHz, then any injected noise in the region up to 90 KHz or so will have an effect on the sound, depending on how fast the response rolls off. But, lets keep this in perspective - one can inject a tiny amount of 60 KHz noise and the damage is causes may not be audible to our ears depending on our ability to hear it and our systems to resolve it, even though the sound did change a bit in the audible octaves.
I can give you a splendid example of this in one of my own designs. About two decades ago I was consulting for a successful audio amplifier company. They had a real winner of a power amp, it was listed in all the recommended components. Their preamp left a lot to be desired though, and that is why I was hired. I sketched out a phono preamp over dinner one night with the CEO of the company and their primary engineer.
I built it a few days later and plugged it into my system. The line stage was about perfect but the phono stage was a bit on the hard sounding side. Try as I might over the next week, I could not find the reason for the hardness. Since we were having a design review on Saturday, I had to fix it and fix it fast. Finally, around midnight on Friday, I found the problem. There was a 6 dB bump in the frequency response at 14 MHz and that is what was causing the hardness. Once I found the source for that, the hardness was gone completely. That bump at 14 MHz caused audible effects in the 1 to 3 KHz range even though at 14 MHz the gain had already rolled off quite a bit, beyond the -6 dB point. The gain was still significantly higher than unity though and that was the problem. Like I said, if it is in the bandwidth of the amp and the noise is bad enough, you will hear it!
Spatialking - Class D is absolutely analog, at least in Icepower or Hypex implementation. I think you're very confused here. We deal with digital when when resolution has certain limits. There is no resolution limit here. Analog voltage signal comes from the input to analog modulator that changes voltage (in linear fashion)to duty cycle WITH UNLIMITED RESOLUTION. Output parameter until filtered is time (duty cycle). Type of parameter does not have any bearing on being digital or analog. Voltage can be analog or digital as well as any other parameter.
Digital implementation wouldn't be even possible since to get 16 bit resolution and 20kHz bandwidth carrier frequency would have to be 1.3GHz (Nobody makes N-channel Mosfets this fast). You can read, Karsten Nielsen (founder of Icepower) doctorate work on principles of Icepower (in English on Icepower website). B&O was so impressed with his work that created subsidiary company for him and gave him stock (private company) first time in their 70 years history. This, and the fact that Jeff Rowland put his name on changing whole production to class D only, makes me believe that it is not so bad (at least for me) and even for very discriminating audiophiles should be satisfactory for subwoofer.
You stated that class D produces other kinds of distortion - could you comment on this? What other kinds of distortion? Do they have name?
Harmonics produced by class D are mostly even (like in tube amp) - just opposite to class AB producing higher order odd harmonics (especially at low levels).
I never said that there is no noise on the output of class D amp. I stated that any amp produces a lot of switching noise and that the one created by class D does not affect the sound. In order to affect the sound something would have to show in FFT of idle noise in audible band (0-20kHz).
It doesn't and Icepower itself is the best proof because it doesn't contaminate itself having idle noise 0-20kHz below -140dB.
No matter what can be measured or proved - the best proof is listening session. Listen to one of top Rowland amps that Guido recommended and prepare to be amazed. Mine is the cheapest one and I think it's great.
I don't have any papers or math or theories to dazzle you with. But I do have a Rowland Capri preamp, 102 amplifier, and PC-1 power correction device and a pair of very high resolution conical horns. These horns only reproduce up to about 14 Khz and, being a 61 year old male, I can't hear anything higher than that. My equipment is deafeningly silent directly into the horn but when I go through my dbx Drive Rack, I hear a faint rushing sound. A recording engineer friend tells me that the dbx has a residual noise floor of -100 db. and that I need line level attenuators to eliminate the sound. I may acquire some of those eventually if the noise ever bothers me enough.
The message I get from this is that my ICEpower amp is silent and my noise is definitely emanating from elsewhere.
Maybe yours is too.
All of this anti-Class D hysteria is ridiculous. There may be poor implementations out there but I have owned Red Wine Audio and JRDG amplification devices for 4 years now interspersed with tube and class A amplifier insertions. My experiences have been uniformly positive and I am beginning to believe that those who decry the increasing presence of Class D have a flat-earth disorder, a profit motive or a faulty theory.
We have, like it or not, passed the point of no return with Class D. It is here to stay and the established modalities are the ones that should be questioning their future.
Napoleon isn't going to return, Mr. Chauvin.
Coffey - Funny that you mentioned Coda because president of Coda in letter to Stereophile after the review (that compared CODA S5 to Bel Canto class D amp) said they are very happy that S5 looked good in comparison with such great amp as Bel Canto. I can dig-out exact quote if you like. Stereophile in another review of Channel Island D-100 (class D) said that it has even ("head to head") performance with CODA S5. There is still chance that Stereophile and other reviewers are deaf but president of CODA? Do you think he is deaf? Frightening..
I have more experience with class D than just about any consumer. With that experience, I can truthfully say class D is the devil himself to get right. After settling onto one manufacturer, I have been trying for 5 years to get the sound to where I am satisfied. Now, having accomplished that a long time ago, I just keep finding the amps have not been fully mined. Right now, I just think there is no tomorrow in improving the sound I have now.
You just can't plunk down a class D amp, and expect it to sound as wonderful as I describe. Any number of components will sicken the class D sound. I can demonstrate that to anyone and have many times.
"i will listen to em again" - to Glen Back and Karl Rove?
Muralman - I agree. It is more revealing. With class D I discovered how cheap $25 aluminum dome tweeter with Mylar cap in series sounds like. I ended up with much better $250 tweeter and $15 capacitor but still with some harshness and sibilants. I changed caps to $100 kind and it becomes sweet and extended plus soundstaging improved. My previous amp was covering it or maybe I did not expect much. Other way around - putting great speakers on cheap electronics and cables will reveal it ruthlessly.
I did go to the Icepower site and I downloaded his thesis. I skimmed through it yesterday and today at lunch and I focused on some of his major points. There is a lot there and he is certainly the first to put phased pulse code modulation into a Class D amp. I can see the advantages of that since it allows one to effectively have a higher sampling frequency while using a lower clock frequency.
But he did not invent phased pulse code modulation! I am pretty certain I worked on a PPCM circuit when I was in the Air Force working on some old DEW radar equipment; I know it has been used in various circuits since then as well.
You asked me to explain distortion mechanisms in Class D amplifiers. Either you did not read the links I posted above or you did not understand them as the biggest distortion mechanisms for Class D are described there. However, given that those papers were written for electrical engineers and not the layman, I think I will describe those in a separate post later. I will also include Class A and Class AB distortion mechanisms since they also apply to a Class D amplifier.
You are correct that Class D is analog, however it is most certainly not linear. Class D amps have much more in common with digital amplifiers or switching power supplies than linear Class AB amps. If I used the word analog in place of linear somewhere I apologize as that would be the wrong term.
However you are absolutely wrong when you think that Class D amplifiers have no resolution limits. Indeed they have at least as much or more than Class AB. The reason for this is that in a Class D amplifier there is a quantization error that exists because the modulator is trying to approximate the area under the analog input waveform in a given time sample using a varying pulse width approach, that is a PWM Rectangular waveform. As soon as you use that approach you develop a quantization error which does not exist in linear Class A or AB amps unless the units are severely bandwidth limited and even then it would not be a quantization error, it would simply be rolled off. I dont know who told you or why you would think a Class D amplifier has infinite resolution but it most certainly does not. There is nothing available at any price, using any form of amplification, such as tube or solid state, in an amplifier which has infinite resolution.
Using the IcePower approach with phased PWM one can obtain a reduction of a factor of four in quantization error, but that does not mean some number X divided by 4 is zero. Hardly! Note that if the sampling frequency was unscaled by four, you would have exactly the same thing as a phased PWM at 1/4 the sampling rate. The big advantage using the IcePower approach is for any given sampling frequency, the effects are equivalent to increasing it by a factor of four, or some integer multiple of that given the number of phased arrays you have.
But there is a trade off here: you cant increase the number of phased array output devices without dealing with increased problems in dead zone, turn on, turn off, rise time, and fall time problems. The more devices you put in parallel the greater problem you have with dead zone and the resultant harmonic distortion that results from it. The paper does mention this.
You also mention that 16 bit resolution with a 20KHz bandwidth is not possible unless you are sampling at 1.4 GHZ? Where did you get these numbers? I have news for you: we have an honest 16 bit systems at 196KHz and 20 KHz bandwidth working in the world today and in consumer gear, too. The big limitation in achieving 16+ bits of resolution is NOT in the digital domain but in the analog. There are few linear or analog ICs available that produce an honest analog equivalent in Signal to Noise ratio of more than 18 bits. Maxim has an audio IC which is guaranteed to produce 16 bits SNR, bu the price of that is so expensive hardly anyone uses it.
Discreet 16 bit SNR circuits are possible but add other issues In short, we are a long ways from true 24 bit SNR on the analog side. The clock speed is just not a problem and neither are the digital chips to run at that speed. Also, if you are speaking strictly in the domain of Class D, there is a LOT more to deal with than just the clock speed. Besides as stated in the thesis, it is clear that an effective 1.6GHz sampling rate is reasonable in production.
I disagree with your statement that only even harmonics are possible in Class D amplification. This is nuts really; if you look at the papers I posted above you can see that a dead zone in the region of 20 MHz to 500 MHz bandwidth causes as much as 2% harmonic distortion and this is not just even harmonics. And we did not even discuss clock jitter, whose effects are amplified by phase shifted pulse code modulation. Besides, the claim that odd harmonics are more audible than even harmonics was dispelled at least a decade ago. Music itself produces both even and odd harmonics as do loudspeakers. The Class D amplifier is very much like a push pull output stage in a linear amplifier, both even and odd harmonics will be produced. Even the thesis published distortion curves which are virtually identical to Class AB amplifiers.
Lastly, you continue to quote to me reviews by noted authors in various stereo review magazines as if that is supposed to prove to me that Model X amplifier is obviously a fantastic product. Frankly, if someone publishes something good about some product, I consider it is worth a listen but nothing beyond that. I hardly think for an instant that just because someone published an article stating that Model X amplifier it as close to perfect as possible and it is indeed so worthy of my cash that I will plunk down money for it. It might be great for their ears but I wear mine, not theirs. Consequently, I listen critically before I spend money.
I quit listening to that sort of review blabber at least 20 years ago when I walked into an expensive stereo salon in Beverly Hills, CA, and the sound there was substantially worse than what I had in my living room. And, the salespeople there were trying to tell me what they had was as perfect as I could possibly buy!
I walked out and didnt bother to spend a dime there, considering when I walked in I was ready to dump, in 1981 dollars, around 600 dollars on a phono cartridge.
You stated that listening is proof of concept, I do agree with that statement but did you read above where I did listen to my amplifier and I came to the conclusion after much listening over a period of time that my bass is somewhat dead and lifeless? I didnt measure this, I didnt read it, I determined that by listening to it. Actually, the Class D amplifier is only amplifier I have yet to put on a bench and test.
Perhaps your bass is fine, perhaps not, I dont know but I can assure you, my bass is not. Frankly, the bass was somewhat better when I had the Amber 70s in the system; at least until they ran out of voltage. It is hard to compare the sound of a 70 Watt amplifier to a 450 Watt amplifier when the 70 Watt amp clips occasionally. To my knowledge, my Marantz Class D amp has not clipped once. But that doesnt change the fact the bass now has a problem.
Kijanki, if you really believe that your Class D amplifier has 140 dB SNR, then do this experiment: take a battery powered AM radio and tune it to a spot on the dial which has no station. Then move it close to your Class D amplifier and see if it picks up any radiated EMI. An amplifier that has 140 dB SNR will not make a sound on the radio.
Frankly, I believe if you got that 140 dB SNR figure from some literature, they sure arent measuring it with respect to 1 Volt! Not to mention the fact that to measure the output of a Class D amplifier, one has to use a very steep filter to squash the noise on the output. Gosh, if I put a 5th order filter cut to 20 KHz on the output of a Class AB amplifier, I would get fantastic SNR too!
My advice to you is to start listening to your ears, accept the fact you can't afford the most expensive gear, and quite accepting reviews as gospel. In the long run, you will have a better sounding stereo and more money in your pocket.