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Can you explain the newer class "D" amps to me?

Q

Quickie

May 6, 2011
569
2
#1
I am a fan of s/s for the reason that they give great dampening factor.....I would go mosfet as compared to more traditional designs. But I see so many adds for the new class d power supplies and the low weight of these units. I'm old school...you need a good transformer and supply capacitors to get good clean power. With the class d design....seems like it's basically a "valve" from the wall outlet?
 
#2
Not sure what kind of explaination you need but my 4 lb GK sounds a lot like my old 25 lb GK, yet it fit's in the pocket of my gig bag. ...means less trips to and from the car Given the amount of crap I generally haul being a PA guy as well, I adore it.
 
#4
I don't begin to understand how the electrical part of all this works but somehow it does. My Genz-Benz Shuttle 6 is a great sounding amp. I am also used to big hulking power transformers and tons of tubes from my 1971 Ampeg V4 so I was very hesitant. I hear that class D is also very dependable. I guess I'll find out.
 
#6
The EA site doesn't explain it at all. This does:
Class D Amplifier - Wikipedia, the free encyclopedia

But what people really want to know is how the power supply works, without a big transformer(but switching supplies still use a transformer, just a much smaller one).
http://en.wikipedia.org/wiki/Switched-mode_power_supply

The answer, in extremely simple terms, is frequency. The switching power supply takes the 60Hz voltage from the wall and chops it up into much smaller pieces, on the order of at least 50Khz. Because of the physics regarding how transformers work, the transformer can be much, much smaller, because it is operating at a much higher frequency than in traditional designs. Yet it will supply as much current as a big transformer that operates at 60Hz. This is an extremely simplified description.
 
#9
dmusic148 said:
The answer, in extremely simple terms, is frequency. The switching power supply takes the 60Hz voltage from the wall and chops it up into much smaller pieces, on the order of at least 50Khz. Because of the physics regarding how transformers work, the transformer can be much, much smaller, because it is operating at a much higher frequency than in traditional designs. Yet it will supply as much current as a big transformer that operates at 60Hz. This is an extremely simplified description.
Click to expand...

Not quite. The mains input voltage is first rectified into DC and THEN is chopped up to make a square wave high frequency AC voltage. That is fed to the transformers.
 
#12
Quickie said:
I am a fan of s/s for the reason that they give great dampening factor.....I would go mosfet as compared to more traditional designs. But I see so many adds for the new class d power supplies and the low weight of these units. I'm old school...you need a good transformer and supply capacitors to get good clean power. With the class d design....seems like it's basically a "valve" from the wall outlet?
Click to expand...

Class-D with SMPS is a black box.
You put a signal in and it comes out amplified. It just so happens that they are light and accurate.

Bass heads with tone controls are going to be pre-EQ'd to what the manufacturer feels will lure you in.
 
#13
Quickie said:
I am a fan of s/s for the reason that they give great dampening factor.....I would go mosfet as compared to more traditional designs. But I see so many adds for the new class d power supplies and the low weight of these units. I'm old school...you need a good transformer and supply capacitors to get good clean power. With the class d design....seems like it's basically a "valve" from the wall outlet?
Click to expand...
yup. Not too far off.

Its either on or off, a series of pulses, the duty cycle essentially determines the avg voltage relative to the supply voltage.

They still have circuits converting the AC from the wall to +/- direct current. The really light ones use switching power supplies to do that, rather than large heavy transformer.

The class D output is way more efficient, when on, no voltage across the output device, and when off, no current flows, so very little power is wasted as heat compared to traditional analog circuits. This means that you need much smaller power supply for same wattage class D amp as traditional output, which also helps keep the weight down, and complements the switching power supply.

Randy
 
#14
I played an outside gig last Saturday using a GK MB500. Power was supplied by a mobile transformer like they use on construction sites. My amp cut out five or six times during the night, though it wasn't hot to the touch and the fan didn't come on. I'm inclined to believe the shutdowns have something to do with inconsistent power supply, as it works fine with in-house AC. I'm playing another outdoor event tonight (97 degrees here) and leaving the little box home - 800RB this time.
 
#15
I am a huge fan of tube amps and never liked SS amps...until SMPS became more common. For some reason, while they don't quite get the depth and feel of tube amps, they have better tubetone-copping abilities. And now that they're making hybrids out of these little amps, I don't think I'll ever own another lead sled SS amp.

However, I do believe that there is something to the idea that the lead sled SS amps have a feel and tone you can't quite get out of the micros, too. My pal Vail Johnson once said on here that he thought all micros were crap because they sagged like tube amps and he doesn't like that sag. Boy did he start a ----storm with that...totally degenerated into a Kenny G bashfest! But I think he may be right, because I like micros better, and that's probably why I do.
 
#16
jeff7bass said:
Why do class D amps seem more susceptable to shutdowns (protect) when given uneven or inadequate voltage?

:confused:
Click to expand...

Because the advanced technology gives us as designers better control over monitoring conditions that may be dangerous to the amplifier's reliability. We now have control of protection parameters on a cycle by cycle basis and the more closely we can monitor the operating parameters for dangerous conditions, the better we can eliminate "blown up amps". The result is longer warranties and better long term reliability. If we could protect the conventional power supply and conventional amp topologies the same way, they would behave the same and be more reliable but we can't. Cycle by cycle control is only possible in the "non-linear" realm.

An amp protecting itself at 90 volts is better than an amp failing at 90 volts eh?
 
#17
Class D amps have many advantages, though rarely do you get something for nothing in electronics ( some things come close however ). Current mode technology had me won first time i implemented a design. As Agedhorse intimates, re pulse by pulse control is one significant improvement.

Try a class D some day, though it would be a bigger power type, amongst other characteristics, the THD rises alarmingly when pushed hard towards their maximum rating.

Given the use of passive crossovers in 2 and 3 way boxes, do wonder about the effects of a class D output stage driving lots of C and medium amounts of L, suppose it comes down to LCR complex impedance at notional instantaneous f ( at some stage an f looks like an instantaneous DC... theory argument not for here... ). What i find amazing is how the designers managed to obtain a functional output stage filter for the switching process over a say a 10 octave range, given the large range of input f and the notional switching rate coupled to high demand slewing rate for the supply rails. That is in plain words, to obtain larger power into nominal load impedance you need higher rail voltages. You need to run the load output terminal(s) up to those rails as quickly as the input signal ( f ) ie input signal changes, how quickly does the output voltage ( and current...oooh wont go there here ). You need high voltage output devices to withstand the combined rail voltages. Starts to become a track and field event with all the compromises and desired outcomes looking to be first over the line.

Do admire the younger engineers whom are bringing product like class D amps to the musicians and PA folk. Impressive, just not convinced these amps are all things to all people, and the older amongst us seen enough to know this....back to my valve/tube rig for some practice... what god invented 20 year old males for...to carry around the sound gear...

Regards to all.
 
#19
Eight_Stringer said:
Given the use of passive crossovers in 2 and 3 way boxes, do wonder about the effects of a class D output stage driving lots of C and medium amounts of L, suppose it comes down to LCR complex impedance at notional instantaneous f ( at some stage an f looks like an instantaneous DC... theory argument not for here... ). What i find amazing is how the designers managed to obtain a functional output stage filter for the switching process over a say a 10 octave range, given the large range of input f and the notional switching rate coupled to high demand slewing rate for the supply rails. That is in plain words, to obtain larger power into nominal load impedance you need higher rail voltages. You need to run the load output terminal(s) up to those rails as quickly as the input signal ( f ) ie input signal changes, how quickly does the output voltage ( and current...oooh wont go there here ). You need high voltage output devices to withstand the combined rail voltages. Starts to become a track and field event with all the compromises and desired outcomes looking to be first over the line.
Click to expand...

This is one area which seperates the men from the boys.

Eight_Stringer said:
Do admire the younger engineers whom are bringing product like class D amps to the musicians and PA folk. Impressive, just not convinced these amps are all things to all people, and the older amongst us seen enough to know this....back to my valve/tube rig for some practice... what god invented 20 year old males for...to carry around the sound gear...

Regards to all.
Click to expand...

Generally, it's not the young engineers who are bringing these products to market. There are a lot of experienced older school engineers leading these projects, using younger engineers as needed, just like in other projects.
 

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