Class D commercial audio amp

I also believe running a class D without a Zobel would not be occasionally deadly to the amplifier like in a commercial class AB linear amp, where there's not a lot of leeway on the size of the output devices, and any significant phase shifts due to the load between the voltage and current waveforms could cause them to punch through the SOA.

I have d "The Class D ampli?cation circuits ensure the LA12X energy-efficiency for minimal heat dissipation. LA12X delivers

I don't see 4 power cords on the back. A power-con of some sort but I'm not sure exactly how it works.

And they are still using RMS watts which should have gone out with the

The audio industry has gone backwards in specs and is dummiing down or maybe the users are dummer these days ? Something ain't right any more.

boB

Loudspeakers sometimes have hidden surprises.

A while ago I had to design a very high quality pre-amp and equaliser system using only E88CC (6922) double-triodes in the signal path (don't ask!). To measure the noise level of the input stage, I had to load it with various resistors, run the valve chain at full gain and connect the output to the 'bench amplifier' which had switchable gain up to over

I found that when I increased the system gain beyond a certain point, the whole lot 'took off' into oscillation. At first I thought the problem was capacitive or inductive coupling to the amplifier on test, but I eventually realise that it only occurred when the audio gain control was turned up. I tracked it down to acoustic feedback into the electrodes of the E88CC, which were very rigid but must have had a high-Q resonance around 40 Kc/s.

The most puzzling aspect of the whole thing was how a rubbishy cardboard-coned ex-television set loudspeaker, squirting noise through a few holes drilled in the metal underside of the bench amplifier, could possibly have been responding acoustically to a watt or less of signal at 40 Kc/s.

heat? "

I would imagine that with piezoelectric or electrostatic tweeters it could create problems due to the capacitive load.

Other than that they are all pretty much inductors, some more inductive tha n others. As already mentioned some of the real elcheapo circuits without e ven inductors do put out EMI, but many of those are in TVs that don't even have speaker outputs. Just shield the case enough and the FCC should leave you alone.

You did mention something about it interfering with hearing aids, which are ow class D. I didn't realize that they had gone class D but it makes sense for batter life. Actually most of them before class D were simple single e nded into the output transducer and they put up with the DC on it because o f reduced component count. When you adjusted the gain on it, going up would increase the DC and going down would decrease the DC. With small shit like that and a high enough frequency they would need no filter. You can't even hear 20 KHz let alone 100 KHz or more.

Actually it might even help. I read a long time ago that some hearing aid m anufacturers were purposely introducing HF AC bias to sort of bias the ears like a tape recorder. Their premise stemmed from the fact that some hard o f hearing folk could hear better when they were near sources of ultrasonic audio, such as near some of the older motion detectors. I can't say how wel l it worked out for them because I never tried one, back then I had good he aring. Now I wonder how something like that would work with my tinnitus.

Another thing though is does this affect your hearing adversely ? Many ties companies like to make things that make people dependent upon then. some h earing loss is caused by the eardrum stiffening up and all that happy shit with the stirrup and hammer, whatever. But alot of it seems to be loss of t he cilia or whatever, little hairs in the cochlea. If you put HF AC in ther e it will be bending those things back and forth and probably cause more of them to break off, thus exacerbating the problem.

If that is so, the solution is not easy, putting a coil and cap in a hearin g aid is not very easy unless the switching speed is extremely high, and it that point the output device will need drive optimization, which requires more components. Damned if you do... you know the rest.

The 1/3 condition is a very severe test, it represents heavily clipped music and using a resistive load. With live music use in a professionally set up system, this condition and the associated AC draw would almost never happen.

The term " watts RMS" is the industry standard way of indicating that the RMS value of a sine wave was used to compute power output - IOW it's true power.

But beware when speaker makers use the same term, they have a whole nuther idea in mind.

.... Phil

Thanks for the link. I think I saw that when I bought the Crown amp recently.

Yeah, 1/8th and 1/3rd. This is new specmanship games for me.

I am used to the old FTC (American) method of rating power ampifiers with sine-waves from 20Hz to 20 kHz like back in the 1970s and 1980s. I would think that the AES would have a standard for power amplifier measurement. Not just Harmon International. I first saw this method when I bought a Crown 1.5 or so kW amplifier hoping that I could get maybe 800 watts out of it. Nope. Soon as it warmed up it did maybe

I will look to see if there is some kind of standard measurement technique these days but I have a feeling that it is a free for all now.

Not 12.0 kW average power. Needs more than 16 amps for that power output.

They would most likely be using 3-phase for that much power I would think. The manual says 4 X 3300 watts so I'm note sure how that works with the one power cable they talk about.

What they really mean is average power. RMS power doesn't exist unless you purposely calculate it out that way and then it doesn't mean what you think it means. They may measure the output with RMS voltage and RMS current into a resistive load and multiply the two together to get average watts, but that is not RMS power. It's average power.

boB

It is a very realistic and thorough way of specing an amp for musical audio use.

Thought so.

Try reading my post again and again till you see all the words.

The term has a clear meaning, defined by constant use within the world of audio that you are stubbornly ignoring.

Question:

Do you imagine that a bottle of "Steak Sauce" contains actual steak ?

Have you complained to the makers or the store when you found it did not ?

The only good thing about absurd pendants like you is it gives the rest of us someone to LAUGH at !!

..... Phil

Not necessarily true.

"Audio equipment salesman" is *way* down the list from "used car salesman" on the reputation-for-honesty list.

Maybe a hundred years ago and perhaps even today in audiophoolland.

He did say "for lab use" in his first post. You even quoted it in your first response.

He's not the only one with that problem, apparently.

Clifford Heath.

Well I'm happy to make you laugh at least :)

No, I'm not using it for audio in this case. I am trying to use it to imitate mains power with transformer isolatation on the output.

It does work, but it looks like in the past 25 years that I have not been in the audio design business in the strictest sense, the method of specifying amplifier power has gone more to "music power" where it used to be that you could actually get rated output power from an amplifier using a sine wave.

I know you've been in audio for a long time and you must remember those days of long ago ?

Actual grid emulation instruments are expensive but are basically just switching subwoofer amplifiers or linear amplifiers with switching mains supplies like the Crown I bought fairly recently.

I'm glad I'm not in the audio business any more. Lots more money and just as much truth probably in making $10,000 RCA cables.

boB

boB, You should be happy that Phil declared you to be a "pendant" rather than a "pedant" >:-} ...Jim Thompson

It could mean nearly anything, including speaker testing and many jobs that are within the capabilities of an AUDIO amplifier.

Plus being a smug troll.

.... Phil

But this stubborn, autistic old duck is just not listening.

Quack, quack.....

.... Phil

Aha... Is THAT why they do this ? What if the amp is powering the woofers of a big PA ? The woofs would typically be fed the same signal wouldn't they ? Since the highs usually don't need as much power as the woofers do, wouldn't it make more sense to have the other channels rated at a lower power ? Or just less channels and smaller amps ?

It's just that the way they are spec'd these days is evidently different than it used to be which was by continuous output at one frequency or wide band noise. So what my bitch is that I cannot trust the power rating of an audio power amplifier to do what I want it to do any more just based on the power rating in watts. I have slowly been finding this out in the past few years cuz I haven't stayed in touch with ratings. I use powered monitors nowadays myself.

Based on the Crown/Harmon link you sent, at approximately 120W output per 1.0 amp of AC line mains draw and 1/8 power pink noise at 230 VAC, it looks like around 2000 watts out for 16 amp input rating. Bridged which is how I'm using them. All those amps are pretty close in that rating.

I-Tech 5000HD, 9000HD, 12000HD Crown amps.

And these amps' idle power asleep is around 60 watts and awake is over 200 watts ! That's quite a lot.

I wonder if anybody is doing a bench review of these amps ? I'm not sure if I would trust anybody in the audio industry to make the kinds of tests I am intersted in though.

It was in the USA as far as FTC (Fair Trade Commission) went, at least in the 1970s and 1980s.

But you're not listening anyway.

Touche' I guess :)

It is raining up here in the Seattle area so I definitely agree.

boB

K7IQ

typically be fed the same signal wouldn't they ? Since the highs usually don't need as much power as the woofers do, wouldn't it make more sense to have the other channels rated at a lower power ?"

To do that requires separate windings on the power transformer. Limiting th e power of an amp stage and still feeding it the higher rail voltage saves you nothing.

Some powered speakers actually do that, and I have seen bi-amp stand alone power amps that do that is well. But at a cost of course.

If they wanted they could make an AC coupled unit for the tweeter off one s ide of the power for the bass amp. That would unbalance the load but they c ould handle that. But it would be one quarter the power at the same load im pedance and I think they want a bit more than that. Or at least some headro om.

Multiple output transformers are comm>>** Multi channel class D audio amps can do continuous sine wave power at their lowest rated impedance long as you do not ask all channels to do the same.

I was simply responding to Phil's assumption that this 4 channel amplifier could onlly supply rated power from one channel at a time as far as playing music was concerned. Assuming that an amplifier is going to be used that way is perposterous.

That's basically what he said from what I am reading in that line.

Power amps used to be rated so I would not have had to ask these questions.

Just seems a waste of amplifier if what Phil was saying was true. I thought he was an expert in this field but I guess not.

boB

Perhaps the 'equal and opposite' reaction to the cone movement in the speaker was conducted through the magnet and speaker frame into the bench and through the amplifier chassis. The voice coil is likely to accelerate normally at 40 kHz, even if the diaphragm is not following it.

That's a possibility; although I seem to remember that waving my hands around between the bench amplifier and the pre-amp affected the oscillation, so perhaps it was airborn sound but radiated by the metal panel of the bench amplifier.