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Class D Switching Power Amplifiers and Power D/A conversion

how are 'cheap' amps built differently?
how are 'cheap' amps built differently?
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Old 19th January 2019, 08:37 PM   #11
FauxFrench is offline FauxFrench  France
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Location: The mountains, calm and quiet.
I guess the car-audio specialists may tell you that one difference between an expensive and a cheap ultra power amplifier is that you can rely on the specs of the expensive amplifier.

With a frequency range up to only 250Hz, you can lower the class D switching (carrier) frequency a lot from the 400KHz-600KHz we use for HIFI and reduce switching losses enormously. Perhaps to some 2KHz-5KHz. Further, you may get away with a single-step conversion of the battery voltage directly to the AC signal output. That will lower power losses and costs as well.

I noticed a documentary from somewhere in central America. People would meet outside of the cities with their vans. The vans were equipped with KW audio installations that made doors vibrate like under a powerful earthquake. All persons had to stay outside and at a distance from the cars and listen from there. Inside the vans the sound level would have caused permanent hearing damage on the spot.
For HIFI-freaks and in particular audiophiles a very different kind of logic.
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Old 19th January 2019, 10:32 PM   #12
NCC74656 is offline NCC74656  United States
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so im repairing a 12000W amp right now, i think its more around 6500W rms. the switching frequency from the driver board is 41.2Khz. is this the switching frequency you are referring to? this is the frequency on the power side of the amp.

there is an audiophile (sound quality) section to car audio. i dont think its worth it however. a car is perhaps the worst place to reproduce music that we find our selves in on a daily basis. there is something to be said for quality speakers and amps but to spend 10, 20, 30 thousand on ultra low THD, high sensitivity, low distortion products in a car is a waste of money imo. in a house you can setup your room to take advantage o such things but in a car... you have your blower fan, your road noise, the large panes of glass all around you, to say nothing of engine and wind noise at 70mph down the high way...
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Old 19th January 2019, 10:56 PM   #13
FauxFrench is offline FauxFrench  France
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OK, 41.2 KHz is higher than I expected. For Hifi we use some 20-30 times the highest frequency we want to reproduce. Perhaps the ultra power amplifiers have another concern that make them switch outside of the audible range - the fear that the magnetic components will generate audible noise directly.

The amplifier you are repairing right now, let's assume it is "only" 6500 Wrms. My 100Ah 12V battery will be drained from fully charged in some 10 minutes. At least I would have that "fun".

Here in Europe we have small cars compared to the US. Those who wants the loudest music are often young persons with a more moderate economy - thus, the smallest cars. Sometimes I hear such a small "boom-box" on wheels. My guess is they have installed amplifiers with a power in the order of some hundred Watts. They hardly have space for double batteries and horse-powers for a larger generator. And, they remain inside the cars.
Is it your impression that cars are frequently equipped with KW audio gear in the US?
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Old 19th January 2019, 11:16 PM   #14
tsmith1315 is offline tsmith1315  United States
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At this point in time, I listen to music in my car about 1 hours per day. At home, I'm lucky to get to listen 5 minutes per week.

Totally agree that there's a limit to fidelity in a car, but the point of diminishing returns depends on your wallet and desire.

FauxFrench:
Car stereo contests are common here in the US, and have evolved quite a bit since the 1980's. The SPL competitions now reach levels of insanity, and have absolutely nothing to do with fidelity. I suppose the ultimate SPL system would reduce the vehicle to a pile of rubble.
I don't really know what's out there now, but a couple decades ago even 2x20W car amplifiers used DC-DC converters to step up voltage to the appropriate level.
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Old 20th January 2019, 08:21 PM   #15
NCC74656 is offline NCC74656  United States
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most audio systems we install is between 500-850W in the budget range. that being said it is quite common to install 1500W systems in the average/every day automotive setups.
as a rule of thumb we install 500-1000w systems with out additional alternator setups and some times up to 1500 in suv's.

its not uncommon to push the 2500w range on the more expensive systems, we frequently recommend alternator upgrades in these setups.

my own personal vehicle i have 6 group 49 batteries and two 420A alternators. these is more on the outside edge of audio systems we work on but to install a couple batteries and a 280-320A alternator is fairly standard.

one issue we run into is the idle vs cruise rpm and people who want to blast full volume at a stop light and drain voltage so much that their engine will shut off.
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Old 21st January 2019, 11:19 PM   #16
FauxFrench is offline FauxFrench  France
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Location: The mountains, calm and quiet.
Thanks for giving me a glimpse of a tradition we do not really have here in Europe.
Just for fun I will show you a typical car for youth where I live: the Peugeot 207 (Peugeot 207 : essais, fiabilite, avis, photos, prix ). Cheap, quite pretty, well driving, economical and easy to get in at the small parkings in the old villages and city parking houses. Typically 80 horsepowers but a torque of only some 160-200. The luggage part at the rear may be replaced with a solid wooden plate for the speakers but then no luggage. No extra battery and standard generator. This is why we cannot follow your tradition. We do not have space and size as you have. But, we can remain inside our cars when we use our car audio equipment and some of us even have some hearing left when we get elder.

Out of curiosity, about how much horse-powers do you have in your car? Your system sounds WILD!

Also here we see high quality audio systems typically supplied in up-market cars. BMW, Mercedes, Volvo, Bentley etc. may be equipped with audio gear from Bose, B&O, Harman Kardon etc. and the sound quality can be impressive. Their competitive edge is rather sound acoustics than raw power. True, if you spend most of your idle time in your car why not put the good stereo there. I guess these up-market systems offer some hundred of Watts and are seldom used to the limit anyway.
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Old 21st January 2019, 11:35 PM   #17
voltwide is offline voltwide  Ireland
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I assume that this car-fi "tradition" is related to urbanization in America. If you live in a flat, there is no way to enjoy real loud music. So you escape into your car, that became your rolling music (and living) room.
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Old 22nd January 2019, 12:11 AM   #18
daqvin_carter is offline daqvin_carter  United States
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This talk of extra alternators and so fourth starts to make a car amplifier made from a Dynaco St70 chassis seem totally reasonable. I ran it with some sort of mosfet amplifier for the low end.
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Old 22nd January 2019, 12:52 AM   #19
NCC74656 is offline NCC74656  United States
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this one is mine. not a typical vehicle but i use it for work (hauling heavy things) and play (driving through rivers, rock crawling, drag racing, and sled pulling).

Click the image to open in full size.
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Old 22nd January 2019, 01:04 AM   #20
NCC74656 is offline NCC74656  United States
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my own vehicle is as follows, its a work in progress so i dont have everything listed here.

5.9L cummins turbo diesel - stroked and bored to 6.4L: shortened/cupped pistons, ARP rod bolts/main studs/head studs. hamiton long duration cam, compound turbos with 93 wheel. coolant bypass kit to relieve pressure at higher rpm's.

full billet 48RE transmission with high energy clutch packs, kevlar shift bands, billet servos/rods/accumulators. shift kit to vastly increase line pressures. teh case has been machined to hold extra clutch packs and bolt together parts that other wise have no positive retention.

axles are dana 60/70 with dana 70/80 internals, electronic locking differentals and 4.11 gearing. over sized axle shafts, external fluid cooling, and upgraded skid plates.

tires are 37" toyo open country MT's. in this picture its got hte smaller 35" nitto grapplers on however.

the body is swapped from another truck due to rust, the interior is from yet a 3rd truck, the bed is original (to be replaced this summer).

the electronics are fully custom. ipod on the dash to control fueling/timming/display gages, statistics, data logging, and allow for on the fly power level changes.

last dyno had 780HP and 1,650 ft/lbs of torque at the wheels.

truck has 567,800 miles on it

weighs in at 10,100 Lbs unloaded (4,581KG)

i started rebuilding this truck about 4 years ago, i have done nearly all the work on it personally and solo. from engine to axles, to body swap... just me for 95% of it. i figure i have about another year or so till im done.

audio so far is: full spray on damping from cascade audio, black hole tile/peel and stick damping, two layers of 3/4" MLV from cascade audio that goes form bottom of windshield to bottom of rear window. single layer 1/2" MLV on inner doors and roof. also a lead seperated base with 5Lbs density rests over the transmission tunnle/firewall/rear wall area.

dual hybrid audio 8.8" lagatias in each door for midbass, 1/4" aluminum plate to cover holes in doors, single 4.75" lagatia mid range in each door, single 1.25" tweeter also in each door. 1000/4 T series rockford fosgate for mid/high, 1000/2 rockford for midbass, both class A/B. sub amp will be a T2500.1 rockford class BD. powering a isobaric mounted pair of Fi audio SP4 3500W (rms) 18" subs in a 6th order 22 cubic foot box in the back seat. finially a mosconi 6-8 aerospace DSP for the processing. i plan to install a 17" touch screen LCD into the dash adn run either linux or windows 8.1 off a mini desktop ryzen/vega system for the radio.

if your looking for some build porn here are the links to my build log of this truck: rebuild of my truck N7 part 2 - Dodge Cummins Diesel Forum

Last edited by NCC74656; 22nd January 2019 at 01:09 AM.
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