Forums

Class D commercial audio amp

Started by N_Cook November 29, 2016
On 11/30/2016 12:34 PM, Jim Thompson wrote:
> On Wed, 30 Nov 2016 17:04:24 +0000, N_Cook <diverse@tcp.co.uk> wrote: > >> On 30/11/2016 15:45, Jim Thompson wrote: >>> On Wed, 30 Nov 2016 10:41:59 -0500, Phil Hobbs >>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>> >>>> On 11/30/2016 07:00 AM, N_Cook wrote: >>>>> >>>>> Should 1.5v remnant 200KHz stay constant with whatever frequency or >>>>> amplitude of audio going in? Even at zero audio input there is this 1.5V >>>>> 200KHz. >>>> >>>> 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 >>> >>> What does that non-zero remnant do to the speaker... produce some >>> heat? >>> >>> ...Jim Thompson >>> >> >> There is what I took to be a Zobel,between speaker line and ground, 2.2R >> 10W in series with 430nF but may be there to absorb some of this remnant >> I suppose > > What is the impedance of a speaker at 200kHz? > > ...Jim Thompson
I believe the purpose of the Zobel in a class D with pre-filter feedback isn't to ensure HF stability by flattening the load like in a class AB power amp, but primarily to reduce the Q of the output LC into high-impedance loads. 430nF ideal capacitance has an reactance of about 2 ohms at 200kHz, so even at no-signal the Zobel R is likely drawing a decent amount of current. 2.2 ohms sounds small to me given the LC values determined above, but then again I don't know what the nominal undistorted max power output of the amp is supposed to be. It is 100% efficient at no signal though! 100% efficient at turning energy into heat
On 11/30/2016 02:14 PM, bitrex wrote:
> On 11/30/2016 12:34 PM, Jim Thompson wrote: >> On Wed, 30 Nov 2016 17:04:24 +0000, N_Cook <diverse@tcp.co.uk> wrote: >> >>> On 30/11/2016 15:45, Jim Thompson wrote: >>>> On Wed, 30 Nov 2016 10:41:59 -0500, Phil Hobbs >>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>> >>>>> On 11/30/2016 07:00 AM, N_Cook wrote: >>>>>> >>>>>> Should 1.5v remnant 200KHz stay constant with whatever frequency or >>>>>> amplitude of audio going in? Even at zero audio input there is >>>>>> this 1.5V >>>>>> 200KHz. >>>>> >>>>> 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 >>>> >>>> What does that non-zero remnant do to the speaker... produce some >>>> heat? >>>> >>>> ...Jim Thompson >>>> >>> >>> There is what I took to be a Zobel,between speaker line and ground, 2.2R >>> 10W in series with 430nF but may be there to absorb some of this remnant >>> I suppose >> >> What is the impedance of a speaker at 200kHz? >> >> ...Jim Thompson > > > I believe the purpose of the Zobel in a class D with pre-filter feedback > isn't to ensure HF stability by flattening the load like in a class AB > power amp, but primarily to reduce the Q of the output LC into > high-impedance loads. > > 430nF ideal capacitance has an reactance of about 2 ohms at 200kHz, so > even at no-signal the Zobel R is likely drawing a decent amount of > current. 2.2 ohms sounds small to me given the LC values determined > above, but then again I don't know what the nominal undistorted max > power output of the amp is supposed to be. > > It is 100% efficient at no signal though! 100% efficient at turning > energy into heat
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.
On 30 Nov 2016 16:55:54 GMT, Glen Walpert <nospam@null.void> wrote:

>On Wed, 30 Nov 2016 04:13:42 -0800, Phil Allison wrote: > >> Rob wrote: >> >> >>> 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. >>> >>> >> ** That has been true for over 20 years now. >> >> The really ground breaking class D amps were the K1 and K2 models from >> Crown - released in the mid 1990s. When bench tested as a "black box" it >> was genuinely hard to tell you were dealing with anything unusual. The >> only give away was the low heat production so the amp needed no fan. >> >> http://adn.harmanpro.com/site_elements/resources/995_1425481007/K1-K2- >Data-Sheet-136713_original.pdf >> >> THD measures about 0.03% at rated power, no switching noise is evident >> at the output terminals and the DF is over 3000 at low and mid >> frequencies. Plus the case is hermetically sealed so no dust ever gets >> inside. >> >> Widely used and still used for pro-audio and home theatre applications. >> >> >> >> .... Phil > >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.)
I have done a bit of looking into switching audio amplifiers for lab use and they don't seem to be quite up front about their power output specifications and power input requirements. Crown for instance does not seem to be specing full output power and AC power requirements... They use something like pink noise at 1/10th full power but don't really ellaborate. Also, audio these days is always specing A-weighted. Something that, when I was in the audio business was rare. At least they should spec A weighted and flat as well. As far as this L-Acoustics LA12X which is supposedly a 12kW amplifier, the input power is say, 240 VAC at 16 amps... This calculates out to 3840 watts input. And this is at HIGH line voltage ! The manual also says... "The Class D ampli?cation circuits ensure the LA12X energy-efficiency for minimal heat dissipation. LA12X delivers 4 x 1400 W RMS at 8 Ohms, 4 x 2600 W RMS at 4 Ohms or 4 x 3300 W RMS at 2.7 Ohms" 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 1970s. 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
> >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 :-).
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:

>...if you're unlucky it might excite higher resonances of the > tweeters.
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 60dB and accurate metering. The bench amplifier was hung above the back of the workbench beneath a shelf, in its underside was a 5" loudspeaker for rough and ready audio monitoring. 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. -- ~ Adrian Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to reply) www.poppyrecords.co.uk
>"What does that non-zero remnant do to the speaker... produce some
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 than others. As already mentioned some of the real elcheapo circuits without even 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 ended into the output transducer and they put up with the DC on it because of 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 manufacturers 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 of 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 well it worked out for them because I never tried one, back then I had good hearing. 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 hearing 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 the cilia or whatever, little hairs in the cochlea. If you put HF AC in there 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 hearing 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.
boB wrote:
> > > I have done a bit of looking into switching audio amplifiers for lab > use and they don't seem to be quite up front about their power > output specifications and power input requirements. Crown for > instance does not seem to be specing full output power and AC power > requirements... They use something like pink noise at 1/10th full > power but don't really ellaborate. >
** Not true, AC current draw a dissipation specs are given for 1/8 and 1/3 power pink noise. http://rdn.harmanpro.com/product_documents/documents/2550_1430861481/ITHD2_Power_Draw___Thermal_Dissipation_original.pdf 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.
> > 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. >
** A single PowwerCon can easily handle the currents involved in actual use.
> And they are still using RMS watts which should have gone out with the > 1970s. >
** Wrong. 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
On Wed, 30 Nov 2016 16:05:13 -0800 (PST), Phil Allison
<pallison49@gmail.com> wrote:

>boB wrote: >> >> >> I have done a bit of looking into switching audio amplifiers for lab >> use and they don't seem to be quite up front about their power >> output specifications and power input requirements. Crown for >> instance does not seem to be specing full output power and AC power >> requirements... They use something like pink noise at 1/10th full >> power but don't really ellaborate. >> > > >** Not true, AC current draw a dissipation specs are given for 1/8 and 1/3 power pink noise. > >http://rdn.harmanpro.com/product_documents/documents/2550_1430861481/ITHD2_Power_Draw___Thermal_Dissipation_original.pdf > >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. >
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 700 watts maximum, down from 1kW. 60 Hz sinewave. 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.
> > >> >> 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. >> > > ** A single PowwerCon can easily handle the currents involved in actual use.
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.
> > >> And they are still using RMS watts which should have gone out with the >> 1970s. >> > >** Wrong. > >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.
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.
> >But beware when speaker makers use the same term, they have a whole nuther idea in mind. > > >.... Phil
boB
boB wrote:

> > > 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. >
** Not it's not. It is a very realistic and thorough way of specing an amp for musical audio use.
> > 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 > 700 watts maximum, down from 1kW. 60 Hz sinewave. >
** So you are not using the amp for music or audio. Thought so.
> > 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. >
** You are one stubborn old fool, aren't you ?
> > > > ** A single PowwerCon can easily handle the currents involved in actual use. > > > Not 12.0 kW average power. >
** Can you read ? Try reading my post again and again till you see all the words.
> > 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. >
** You related to ducks by any chance ?
> > >> And they are still using RMS watts which should have gone out with the > >> 1970s. > >> > > > >** Wrong. > > > >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. > > > 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. >
** But the wording is "watts RMS". 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
On Tue, 29 Nov 2016 10:12:28 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:

>On 29 Nov 2016 17:02:55 GMT, Rob <nomail@example.com> wrote: > >>Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote: >>> On Tue, 29 Nov 2016 16:03:40 +0000, N_Cook <diverse@tcp.co.uk> wrote: >>> >>>> >>>>Using PWM input to a Si8244BB predriver soic. After the inductor HF cut >>>>filter, on the 8 ohm speaker load there is about 1.5V pk-pk 200Kz >>>>constant level of switcher waveform, is that normal? what sort of >>>>background level would be normal ? >>> >>> "Class-D" isn't "audio"... the "D" stands for "distortion" >:-} >> >>Why? Of course a Class-D amplifier could have better linearity than >>a Class-A or Class-AB can achieve. > >(1) The damping factor sucks the most sour of lemons ;-)
Not necessarily true.
> >(2) And your "better linearity" claim has the same engineering fact >level as would be put forth by a used car salesman.
"Audio equipment salesman" is *way* down the list from "used car salesman" on the reputation-for-honesty list.
>(3) Class-D pros: low heat, small size, CHEAP, thus manufacturers of >consumer grade (aka junk) audio products love it.
Maybe a hundred years ago and perhaps even today in audiophoolland.
On 01/12/16 11:49, Phil Allison wrote:
> boB wrote: >> 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 >> 700 watts maximum, down from 1kW. 60 Hz sinewave. > ** So you are not using the amp for music or audio. > Thought so.
He did say "for lab use" in his first post. You even quoted it in your first response.
> ** Can you read ? > Try reading my post again and again till you see all the words.
He's not the only one with that problem, apparently. Clifford Heath.