I am currently working on a circuit that seems to be capable of very high bandwidth compared to class D.
I have noticed that class D often starts to some bandwidth dependent distortion well inside the audible range. Most of them stop at 40-80kHz, and the typical result of this is that they also get phase distorsion from around 1-5k, distorsion in frequency response in the same area, rising output impedance (if not corrected heavily with feedback) and some instability problems at the highest frequencyes when being run with capacitive loads.
I think moving the bandwidth up with a factor of 10 or so could mostly solve all this. The design I am working on seems to be capable of that without creating more noise or loosing efficiency.
Does anyone know of any current switching amplifier design capable of this? There is no reason for me to put down a lot of work in something that other people have solved in a similar or a better way allready.
The goals for this are:
-Low output impedance in the entire audioband without heavy or non linear loop gain.
-Power bandwidth of at least 300kHz.
-RF noise similar to, or less than an ICE-power.
-Flat frequency response and phase.
-low impedance capacity to at least 40kHz without stability problems.
Thanks
I have noticed that class D often starts to some bandwidth dependent distortion well inside the audible range. Most of them stop at 40-80kHz, and the typical result of this is that they also get phase distorsion from around 1-5k, distorsion in frequency response in the same area, rising output impedance (if not corrected heavily with feedback) and some instability problems at the highest frequencyes when being run with capacitive loads.
I think moving the bandwidth up with a factor of 10 or so could mostly solve all this. The design I am working on seems to be capable of that without creating more noise or loosing efficiency.
Does anyone know of any current switching amplifier design capable of this? There is no reason for me to put down a lot of work in something that other people have solved in a similar or a better way allready.
The goals for this are:
-Low output impedance in the entire audioband without heavy or non linear loop gain.
-Power bandwidth of at least 300kHz.
-RF noise similar to, or less than an ICE-power.
-Flat frequency response and phase.
-low impedance capacity to at least 40kHz without stability problems.
Thanks
Snickers-is said:
Compared to your 1st post of "Most of them stop at 40-80kHz"
There are some power bandwith charts on my site:
See this Page
That's for the small chips run at 12V with the typical filter. I have not tested the bigger chips.
Snickers-is said:
Oh, OK. I thought you meant switching frequency, sorry.
Yes, I'll have to dig them up. Of course they don't look nealry as good, some of that is due to the nature of measuring class-d signals. But a lot of amps suffer in the top end, no matter what the topology.
The amps are bridged, (BTL). So they get more power.
Another possible advantage of BTL amps is that an output filter may not be needed. As the RF is the same polarity on each line, there should be no RF current flow. The speaker sees onlly the difference, which is AF.
However, with speaker wires over about 10 inches, you'll raditate a lot of RFI! Sheilded speaker cable, maybe? =)
More power bandwidth
I have been thinking a lot about reducing my efforts to further develop new class A power amplifiers due to the high cost of energy and thus put my efforts into class D or other high efficiency circuit design.
I would be willing to work on a project that improves the bandwidth of such designs since I feel it very important to have low intermod and distortion figures well above the normal hearing range. One of the questions that would need to be answered is, would such a project lead to a commercial product or would it be made freely available to everyone?
Johannes Fassotte
Fairbanks, Alaska
I have been thinking a lot about reducing my efforts to further develop new class A power amplifiers due to the high cost of energy and thus put my efforts into class D or other high efficiency circuit design.
I would be willing to work on a project that improves the bandwidth of such designs since I feel it very important to have low intermod and distortion figures well above the normal hearing range. One of the questions that would need to be answered is, would such a project lead to a commercial product or would it be made freely available to everyone?
Johannes Fassotte
Fairbanks, Alaska
It is good to hear that you pay attention to these things. The question of putting the benefits of a class D and the benefits of a class A together is mostly what drives me in this direction.
I think it is a very bad idea to just post the schematics on the forum right away. I have sent you an e-mail.
BTW, your website seems to be out of order.
I think it is a very bad idea to just post the schematics on the forum right away. I have sent you an e-mail.
BTW, your website seems to be out of order.
Re: More power bandwidth
... that's for the participants to deside. Turning something into "commercial" in the true sense requires rather much money so start somewhere in a small scale when you can afford to loose money. I'll guess Hypex has put a lot on money in thier UcD modules, likewise ICEPower and Anaview .alaskanaudio said:
You are right about that peranders. It is not only to say: Hey world, I have a good product, come buy it!
However, I think it would be a good idea to apply for a patent on this one. What the thread is really about is:
-Does anyone know any technology that is able to perform really well at high frequencies?
-Have anyone done tests with high bandwidth amplifiers to determine the true effect it has on the high end of the audio band?
However, I think it would be a good idea to apply for a patent on this one. What the thread is really about is:
-Does anyone know any technology that is able to perform really well at high frequencies?
-Have anyone done tests with high bandwidth amplifiers to determine the true effect it has on the high end of the audio band?
Most healthy people will hear a 3dB error at 10kHz without any problem. But an amplifier is more than a frequency response curve.
The ammount of distortion is a result of many different bandwidth dependent contributors, but as you probably also know they are not all being improved by a higher switching frequency. If that was the case, all class D amplifiers would have at least 2-5 times higher bandwidth resulting in lower distortion.
The key to solve many of the distortion problems must be to remove or supress the distortion contributors that makes distortion rise at higher switching frequencies, and then raise the switching frequency.
As you mention too, the efficiency as a result of non linearities in the output FETs are an issue. In an output stage some of these factores depend on both the transistors themselves and the circuit design. This also calls for redesigning the output stage.
Many interesting attempts have been made throughout the years, but it is a bit hard to know or to predict the outcome of those. Since PWM amplifier business is dominated by class D configurations it is likely to believe that these are still the best at audio performance.
The ammount of distortion is a result of many different bandwidth dependent contributors, but as you probably also know they are not all being improved by a higher switching frequency. If that was the case, all class D amplifiers would have at least 2-5 times higher bandwidth resulting in lower distortion.
The key to solve many of the distortion problems must be to remove or supress the distortion contributors that makes distortion rise at higher switching frequencies, and then raise the switching frequency.
As you mention too, the efficiency as a result of non linearities in the output FETs are an issue. In an output stage some of these factores depend on both the transistors themselves and the circuit design. This also calls for redesigning the output stage.
Many interesting attempts have been made throughout the years, but it is a bit hard to know or to predict the outcome of those. Since PWM amplifier business is dominated by class D configurations it is likely to believe that these are still the best at audio performance.
peranders said:Welcome back Johannessee also here
PA thank you for welcoming me back to the DIYAUDIO forum. I have been very busy with other things including some software development for control of remotely located satellite tracking antennas and designing the software for another commercial remote control application.
On the subject of improving wideband performance of class D audio power amplifiers.
I agree that if the purpose of a design is to get a patent then the less people involved the better. My idea for a wide bandwidth class D amplifier would be to completely eliminate the dead time by changing to a fixed bias during the normal dead time to the maximum degree possible depending on how fast switching to this mode could be performed. This would dictate the requirement to control the output stage and drivers precisely which would mean a total redesign of presently used class D output stage and drivers. Other methods way become obvious when such circuits are prototyped and evaluated in MultiSim or other simulation software. Such a circuit would be a good marriage between class A and class D. When I have a little more time I will use MultiSim to see what results I get and what Ideas I can develop from the results obtained.
Johannes Fassotte
Fairbanks, Alaska
Alaskan Audio
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