Well, you could cascade additional sections to get a steeper rolloff--three sections would get you about a factor of a million (120 dB). The group delay (phase nonlinearity) tends to get worse though.
For extra credit, you could put a notch at the switching frequency by parallel-resonating one of the inductors at 200 kHz. Since the waveform is far from sinusoidal, I'd expect that to hurt rather than help--the parallel capacitor takes over at high frequency, so you lose the benefit of the inductor at the higher harmonics.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
hobbs at electrooptical dot net
http://electrooptical.net
and modify between the TV and the Sennheiser transmitter to shape the frequency response? ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| STV, Queen Creek, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I'm looking for work... see my website.
Sure, why not? A TCA0372 would give you all the volume you could need.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
hobbs at electrooptical dot net
http://electrooptical.net
The output impedance can, as with any amplifier, be decreased using feedback. In this case the feedback point has to be behind the filter.
Of course not. It is much easier to design a very linear voltage-to- dutycycle converter than a linear power amplifier.
That does not have anything to do with the achievable quality, doesn't it?
Today, Class-D is not only used for small amps in a consumer device, it is used in high-power stage amplfiers as well, and the high-end audio people love them.
The really ground breaking class D amps were the K1 and K2 models from Crow n - released in the mid 1990s. When bench tested as a "black box" it was ge nuinely hard to tell you were dealing with anything unusual. The only give away was the low heat production so the amp needed no fan.
formatting link
THD measures about 0.03% at rated power, no switching noise is evident at t he output terminals and the DF is over 3000 at low and mid frequencies. Plu s the case is hermetically sealed so no dust ever gets inside.
Widely used and still used for pro-audio and home theatre applications.
it is used in high-power stage amplfiers as well,"
Class D with SMPS lends itself to that application very well because of the light weight. They are moved around alot. People are getting weaker. Being able to bench press 400 does not help you get one of those racks out of th e van. In fact working out instead of doing actual hard work could make you more prone to back problems.
An Icepower amp made by B&O of about fifty real watts (FTC and IHF do not a pply to "professional equipment") is smaller footprint than a CD, and total ly self contained. Put the AC in, the signal and connect the speaker. It is an attractive solution for engineers who don't want to do the actual work.
audio people love them. "
Not all of them. Some shun them like the plague and I bet some can actually tell the difference. but then these are the same type of people who could tell the difference between regular AB or A amps anyway, as demonstrated by Bob Carver a long time ago.
Some say the high end sounds shrill, or some similar adjective and I can se e why. That output pi filter must have some effect they can hear. Some of t hese people are the same type who change their output transistors to ones w ith a higher ft and say they can hear the difference.
Some ears are different than others. Generally 20 KHz is considered the upp er limit, but is it really ? How steep is the rolloff ? Plus some people co uld be specifically listening for certain things just like alot of people c an hold a conversation with one other in a room with 100 people talking.
Put it this way, if you were to match RMS levels of a 10 KHz sine wave and a 10 KHz square wave and can hear the difference, you might just hear the d ifference in a class D amp.
Bob Carver found a bunch of these golden ears ad challenged them that he co uld duplicate the sound of each and they would not be able to tell the diff erence. It had already been established that they could hear the difference between for example a Mark Levinson and a Crown or whatever. Well he did i t, and did it by just measurements. He had to treat the amp as a black box and measured phase shift, damping and whatever else.
But he did this all in the A/AB domain. I am not so sure it is even possibl e to match it up very closely in class D unless you get the switching speed way up there.
there are people who prefer the sound of vinyl and that ight not all be tha t they like the noise and distortion. Vinyl has a natural rolloff at the hi gh end, whereas a CD drops like a rock. It has to because of the low sampli ng rate. Oversampling and digital filtering may have improved things but th ere are still only 44,100 pieces of information every second. Now they have formats that are much better and some claim to be able to hear the differe nce and I a sure there have been some double blinds done on it. If I were t he manufacturer I certainly would do it. Of course I might find one out of a thousand people who can really tell the difference but that would be in a ll my ads. The type of people Carver found all those years ago.
My hearing is to the point where it simply doesn't matter. You could run a class D at 40 KHz and it would probably sound fine to me. On certain materi al I can barely hear the difference between the 10 KHz on a ten band EQ bei ng all the way down and all the way up. That is at least 20 dB.
Supporting my assertion of course is the fact that people with good hearing do not go in for hearing tests. We don't know if they can hear higher than 20 KHz. Some audiophiles do, and even though they sometimes do not test al l that good, they can still tell the difference in different amps etc. What is the rolloff ? If they are down 10 dB at 20 KHz, what is it at 30 KHz ? Down 18 dB maybe ? Or is there some steadfast rule that says that absolute ly nobody can hear that, perhaps based on the anatomy of the human ear ? Ev en that is not really provable because not everyone has the same anatomy.
AFAIK unless the amp has some fashion of automatic shutdown after the audio signal is removed for a time, the modulator and output stage will always be active.
With no input signal the output waveform will just be a 50% duty cycle square wave at 200kHz, so yes I imagine you'd still be seeing the residual at the load terminal.
There are topologies in some commercial designs that do not present a continuous conversion frequency ripple amplitude.
Ternary modulator topologies generally don't - one type being employed in Crown/Amcron SMPAs is an example.
This is invisible as far as audio performance evaluation is concerned, but has advantages in efficiency, weight and emc. Some implementations require more parts.
square wave at 200kHz, so yes I imagine you'd still be seeing the residual at the load terminal. "
I read somewhere about another type of class D that did not have the consta nt 50 % duty cycle. This scheme reduces the duty cycle at low levels and ru ns like a low bias.
Seems to me this is not easy to implement ad I don't know where they are im plementing it, but it does seem like it would be more efficient.
In other words, a quiescence the duty cycle might only be 1 % positive and negative. When a positive signal comes it increases the positive duty cycle and the same for negative.
Seems like it would even be more efficient than Crown's circuit which uses two output chokes per channel and the damping diodes dump back into the oth er leg of the power rails. I am not so sure that patent is any good though because I have seen other class D amps with two coils per channel. However those could have been two stage filters, I do not know. I rarely work on cl ass D amps because of the possibility of wasting silicon. I do not have the right equipment to cold test it. If I did, I would but the employer is not going to buy the stuff and I am not buying it for him.
Actually, because of the nature of the beast I think many problems in class D amps are caused by bad solder connections. high frequencies and currents destroy the best of solder, even that silver bearing Tektronix stuff. When you got the lead free stuff it is much much worse. And then it is almost i mpossible to tell when a connection is bad by looking at it, I find it bett er to actually troubleshoot it down. Resoldering everything is a bad option .
But bad connections to the base or gate of switchers will kill them. To the other terminals the heat generated might do them in.
I almost want to say to resolder them periodically but most stuff today is built in a pan, meaning there is no access to the bottom without removing t he whole board. Then frequently testing is impossible. You might see it wor k a little bit but with no fan you can't do a high power check or any of th at.
Eventually it will all be like toasters. We used to tell people about VCRs that it is not a toaster, but the price made it so.
Right now B&O is charging good money for those Icepower modules but in time as other people start building them the price will come down. They want li ke $100 for the fifty watt version, hundred watts into four ohms. The thing is smaller than a 1960s transistor radio, and I mean AM only, littlest thi ng out there. Two chips, two coils, one transformer, three transistors and a few twelve cent components. Someone is going to take them out of the game sooner or later.
Interesting, yeah it seems like they'd have thrown some clever techniques at the problem by now, particularly in the higher-end stuff.
Once you add a DSP to the mix, rather than doing the modulation stage in analog, that probably opens up a lot of possibilities. Sample the input waveform into memory, and then you basically have a DAC driving two switches. At that point I imagine if one were clever (more clever than I am at least) you could do all sorts of DSP hacks to create a "botique" switching waveform which was still perfectly reconstructible, but was otherwise optimized to minimize stuff like no-signal output level, harmonic rejection, spread spectrum, etc.
Don Lancaster (who used to post here) had a series of articles on "magic sinewaves", where through some rather challenging mathematical optimizations you could create a PWM representation of a sine wave where you could force many of the non-relevant harmonics to zero through careful selection of the switch event timing.
It'll probably be at its worst near zero output, because the switcher is producing a symmetrical square wave. At nonzero outputs, the amount of fundamental in the output goes down, and the second harmonic goes up.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
hobbs at electrooptical dot net
http://electrooptical.net
What does that non-zero remnant do to the speaker... produce some heat? ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| STV, Queen Creek, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
There is no fool quite like an audiphool.
Sound companies in the US seem to favor the L-Acoustics V-DOSC Line Array system, which is all digital and cannot be matched for sound quality at large outdoor concerts by any analog system ever made. They have recently introduced a 12 kW digital amp, but mostly I have seen 2 and 4 kW in the field (you need a lot of them) with on the order of 100 kW total amplifier capacity but only about 10 kW generator load during a loud concert for ~ 10k audience. (Sound having a separate generator is left over from the era of incandescent lighting with big SCR dimmer packs dumping HF noise into power lines, which would go right through the old analog amplifiers. Totally pointless today.)
Setup of these systems at outdoor concerts starts with entering a topo map of the concert area with speaker tower locations and height. The setup program then calculates optimal angles for each element in the speaker line arrays. After the speakers are hoisted at the prescribed angles and connected a pink noise source and a wireless microphone carried out to designated spots on the topo map are used by the setup program to automatically adjusts levels for flat response across the full concert area. Monitor setup is a bit harder :-).
What is the impedance of a speaker at 200kHz? ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| STV, Queen Creek, AZ 85142 Skype: skypeanalog | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I'm looking for work... see my website.
Yes, and if you're unlucky it might excite higher resonances of the tweeters. That's really bad in woofers, dunno if it matters at the high frequency end. We seem to have a bunch of audio guys coming out of the woodwork who will probably know that.
I have an unused matched set of electret omni mics (Earthworks) left over from a project 15 or so years ago. Their claim to fame was a super clean and fast impulse response (10 us FWHM iirc, good to 40-50 kHz).
I was going to try to use the Helmholtz resonance (*) of the box of a delivery truck to measure how full it was, but the project never got funded. (It only works in certain circumstances anyway. We've all seen small but valuable boxes mounted on their own pallet in swathes of plastic wrap. That takes up a lot of floor space but not much volume, so it wouldn't move the resonance much.
Cheers
Phil Hobbs
(*) The Helmholtz resonance is of the mass-spring type, the sort you get by blowing across the mouth of a beer bottle. The mass is the air in the neck, and the spring is the compression of air in the bottle proper, which goes as 1/(free air volume). This resonance is always lower than the organ-pipe resonances. so it's easy to find.
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
hobbs at electrooptical dot net
http://electrooptical.net
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