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-   -   how they do that? (http://www.diyaudio.com/forums/solid-state/1699-how-they-do.html)

JBL 2nd January 2002 03:59 AM

how they do that?
 
hey,

Does some of you already seen some amp from crown.
Especially the k series. How can they produced so much output and their is NO air cooling the case is completly closed. And yet it's still pretty cool for an amp.

In my opinion this Balanced current deviced must be some sort of class c amp like the current dumping (i think it's called that way). Does nayone got info on this i would like to see that.

Musher 3rd January 2002 08:15 PM

My guess is that they have the amp in class H. That means multiple operating voltages, which are switched on only when needed.

An amplifier with 100V operating voltage produces 96W heat when it drives 4 Watts into 4 Ohms. The smaller signal level, the worse efficiency.

Same amplifier with switchable 50V and 100V would only make 46W heat in that case, so the cooling problems are practically those of a four times smaller amplifier (that is, one that operates with real 50V all the time), with the exception of peak power.

-Kimmo S.

annex666 8th August 2002 12:44 AM

Quote:

how they do that?

MIRRORS!

Sometimes we all need a little cheap humour at quarter to two in the morning - I need sleep!

roddyama 8th August 2002 01:08 AM

2 Attachment(s)
Hey JBL (Love your speakers),

The link below is to the Crown site. In the K-Series amps, they are using a variation of the Class-D (Switching PSU) type configuration (Super Efficient). You'll see what looks like Common-Mode-Chokes to filter out the switching noise yet allow the "DC" through to power the dynamic rails.

http://www.crownaudio.com/amp_htm/kinside.htm

Sony had a class-D out in the early 80's. There were others, but I can't think of them just now.

Here's a pic of the Sony.

Rodd Yamas***a

JonMarsh 8th August 2002 03:37 PM

The K series do not use a switching PSU, they use a variation of CLASS D amplifier. The PSU is a quite conventional linear one with toroids.

Gerald Stanley's innovation in the design of the BCA Class D circuit is using two inductors connected in series; the center point being connected to the output, the ends being connected to the upper and lower transistors. Under idle conditions both transistors are turned on and off for 50% duty cycle, but they are actuallly controlled from ramp comparators running anitphase. So, at idle, both turn on and off at the same time. Current circulates thorugh the inductors, but there is no net output. With a signal, the PWM duty cycle on one set of transitors increases, while on theother set it decreases.

This configuration has several interseting advantages over a conventional half bridge or full bridge switching amplifier output stage as used by most companies.

First, it's impossible to have cross conduction through the half bridge, which is the bane of a conventional half bridge circuit, and makes the driver performance and timing quite crictical.

Second, the effective modulation ripple frequency seen going into the output smoothing filter is double that of the actual transistor switching frequency. This has the expected benefits as regards filter component requirements and HF output noise.

Third, it's possible to add additional phases interleaved, and reduce both distortion and HF noise without having to switch the transistors any faster.

There used to be a pretty comprehensive technical white paper on their site, and downloads of Gerald Stanley's conf. papers. But since Harmon has taken over Crown, things look a lot different, and the technical content is really dummed down.

Regards,

Jon

sam9 9th August 2002 12:05 AM

sam9
 
There are a number a ways to make very efficient amplifiers: Class G and H are variations on rail switching, Class D is pulse width modulation (which someone else other than me will have to explain), and then there is B.A.S.H. which seems to be class D on steroids. You can insert the whole story ( pro and con) of B. Carver in here somewhere, as well.

At this point I gather none of these have a noise level that will meet audiophile levels of acceptability. The noise levels do seem to be comming down over time. Recently Doug Self published plans for a 50W class-G that is better than pervious efforts but by his own admission still falls short of really good class AB performance. There are very practical motives for all of these efforts with the advent of home theater systems where 5 or more 100+W amps need to be squeezed into a single box.

When we are dealing with only two channels, these schemes don't seem worth the trouble. But with multichannel systems, I think you will see a lot of market pressure to move in this direction. I predict (for whatever that it worth) that they will work their way into mid-fi and slowly, painfully, reluctantly into the higher-end world.

Actually, this may be a good challenge for experienced DIYers. Start with Self's scheme and see what can be done to push the noise envolpe in one direction and the power envelope in the other. Personally, I hate the looks of the ubiquitous 19" x 6" x ~16" rack-based box -- I would really like to see good equipment in something on a substantially smaller scale without having to sacrifice power.

Nelson Pass 9th August 2002 06:56 PM

The rationale for these alternative circuits is mostly
energy efficiency.

I have built them all, and can say with some authority that
none of them saves all that much energy over plain old
Class AB circuits with stupid linear supplies when used
for music.

If you are running continuous waves into industrial
equipment for long periods of time , it makes sense,
but if you are really serious about saving energy in
an audio system, use speaker drivers with greater
sensitivity.

You can dissipate 1100 watts driving an 80 dB speaker
with a switcher, or you can dissipate 200 watts driving
a 90 dB speaker.

sam9 9th August 2002 07:15 PM

Even if the energy savings don't matter that much for home use, don't you still gain something by being able to reduce the size of the the transformer and the heatsinking? Some of the multichannel amps and AVRs have grown rather inconveniently large. I'm not an engineer but an industrial accountant by profession. It's not rocket science that big ticket items are the sinks, x-formers and an enclosure to hold them. Except for the for the filter caps in the PS, the passive components are pretty much chicken feed and the in quantity the active components aren't too much more. In mass market quantities, reducing the size and mass of these three or four big chunks of metal are should be pretty significant. Not to mention that there is a population that would apprieciate quality products even at a significant price but as a practical matter simply can't deal 50-100 lb 19"x19"x8" amplifiers.

I think if you just look at the cost of reduced electric bills you miss the bigger issues.

planet10 9th August 2002 07:55 PM

Quote:

Originally posted by sam9
I think if you just look at the cost of reduced electric bills you miss the bigger issues.
IMHO, these strategies still have a ways to go before they sound as good as a well executed Class A or AB amp. Small amp(s), efficient speakers is the way to go.

dave

willryu 9th August 2002 07:57 PM

Balanced Current Amplifier (BCA) info
 
Crown has a white paper on their BCA:

http://www.crownaudio.com/pdf/amps/bcapaper.pdf

A simpler overview of BCA topology is here:

http://www.crownaudio.com/amp_htm/amp_info/bca.htm

-willryu


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