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Old 30th May 2003, 10:34 AM   #1
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Default "Power Tracking" in supply, ever heard, DIY ideas?

Hi!

I just saw this amplifier module
http://www.lautsprechershop.de/hifi/det500.htm]RCM DT500[/URL]
or
http://www.lautsprechershop.de/hifi/index.htm?http://www.lautsprechershop.de/hifi/bau_rave.htm#raveland]PDF about amp[/URL]

, and the site / shop stated that by using a "Power-Tracking" supply, this amp was capable of reaching Class D efficiency in standard class AB topology (and if I take a look at small size of the heatsink, and if the output power of 500W RMS is true, what surely must be the case).

I find that very interesting, does anybody know if the DIY community has something to offer in this regards?

Bye,

Arndt
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Old 30th May 2003, 10:40 AM   #2
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well, it seems vBCode can't handle those URLs properly, even after manually editing...
so, here again:
http://www.lautsprechershop.de/hifi/...ifi/det500.htm

and

http://www.lautsprechershop.de/pdf/detonation/dt500.pdf
(this one should have worked... anyway...)

Bye,

Cradle
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Old 30th May 2003, 12:13 PM   #3
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Ever seen a carver cube?

Works the same way.

A number of high power amps use either multiple power supplies
or adjustable power supplies to get the efficiency up.
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Old 30th May 2003, 12:39 PM   #4
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Default Re: "Power Tracking" in supply, ever heard, DIY ideas?

Quote:
Originally posted by Cradle22
Hi!

I just saw this amplifier module
...URLs deleted...

, and the site / shop stated that by using a "Power-Tracking" supply, this amp was capable of reaching Class D efficiency in standard class AB topology (and if I take a look at small size of the heatsink, and if the output power of 500W RMS is true, what surely must be the case).
Arndt -

The idea behind this - and it is a theoretically sound one, if not practically so! - is that the voltage of the output stage rails is varied in proportion to the signal input to maintain the minimum amount of Vce across the output stage transistors (or Vds across the FETs...). One therefore gets the efficiency of Class D with the superior linearity of Class A (or, at least, this is the idea). The problem here is not unlike the most frustrating one facing Class D circuit designers: how to get the switchmode power supply to respond quick enough to make a difference! The pole-zero compensation of the SMPS' error amplifier is where most of the trouble can be found, and when one finally confronts all the variables that interact - switching frequency, output capacitor size, leakage inductance, output filter inductance vs. current, stabilization against load variations, etc... - most designers have the good sense to shelve the idea.

Gilmore - Bob Carver is the most prominent proponent (was?) of this particular idea, but the product you referred to wasn't on the market for very long, IIRC, so presuming that everyone should be familiar with it is a bit, well... presumptious!
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Old 31st May 2003, 11:29 AM   #5
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"Bob Carver is the most prominent proponent (was?) of this particular idea, but the product you referred to wasn't on the market for very long, IIRC, so presuming that everyone should be familiar with it is a bit, well... presumptious!"

The M400 (Carver Cube) was made for about ten years. All the other models above 100 watts use the same idea. The M1.5 put out 1.2KW bridged, and twice that on peaks.

The only heatsink the M1.5 had was the bottom of the chassis that the output transistors bolted to, no fins, nothing. The PM1.5(pro version) added balanced inputs and a tiny 2" fan with what looked like a toy slot-car motor on it, the fan just sucked air in through the back and out a slot on the front panel.

Rail voltages on the M1.5 were ±37V, ±77V, ±125V, so in bridge mode the amp could swing 400V peak-to-peak on transients(2.4KW/8R).
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Old 31st May 2003, 01:08 PM   #6
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Default Re: Re: "Power Tracking" in supply, ever heard, DIY ideas?

Quote:
Originally posted by jeffreyj
The problem here is -snip- how to get the switchmode power supply to respond quick enough to make a difference!
Here's how I would do it if I were doing it, which I am not.
The bitstream that is coming out of your CD player and into the dac, have it first go into a cheap-and-nasty dac, the output of which controls the supply rail voltage with a fast attack slow decay setup. The bitstream then gets clocked through a delay line (say a static ram or whatever) and gets delayed for 1 second then finally gets to the proper dac that makes the music.

The point is, the supply rail voltage is given a 1second view into the future. It knows what is going to happen 1 second *before* the "proper" dac actually makes it happen. That means the power supply doesn't have to respond so terribly quickly. Heck, you could use triacs to switch taps on the power tranny secondary if you really wanted to go low tech. Lower noise than a switchmode supply. Easy for diy too.
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Old 31st May 2003, 03:29 PM   #7
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Default Re: Re: Re: "Power Tracking" in supply, ever heard, DIY ide

Hi!

Quote:
Originally posted by Circlotron

Here's how I would do it if I were doing it, which I am not.
Disappointing . Actually when I posted this, I was kind of hoping that you would pick this up and tried implementing something... for the benefit of us all...

Quote:

The bitstream that is coming out of your CD player and into the dac, have it first go into a cheap-and-nasty dac, the output of which controls the supply rail voltage with a fast attack slow decay setup. The bitstream then gets clocked through a delay line (say a static ram or whatever) and gets delayed for 1 second then finally gets to the proper dac that makes the music.

The point is, the supply rail voltage is given a 1second view into the future. It knows what is going to happen 1 second *before* the "proper" dac actually makes it happen. That means the power supply doesn't have to respond so terribly quickly. Heck, you could use triacs to switch taps on the power tranny secondary if you really wanted to go low tech. Lower noise than a switchmode supply. Easy for diy too.
Mhhhm... Since I use my Soundcard in a somewhat unusual way, as a freely programmable DSP, it would be no problem at all giving a signal with no delay on one output, and a signal with a delay though a delay tramline on another output...

But since I can only dupe designs already developed - I have very basic knowledge of electronics - that would not help me very much...

I remember from the TriPath chips that they used a somewhat similar approach on "monitoring" the actual output of the power transistors, and adjusting all parameters according to that output...

Sadly TriPath is very deep into debts, and development seems to have slowed down a lot, if not altogether stopped...

Bye,

Arndt
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Old 31st May 2003, 04:06 PM   #8
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I too have been researching the net on how to implement the power tracking system that you are mentioning.QSC has schematics of its Class H amplifier online namely the RMX 2450.It uses a comparator to sense the output and raise the voltage when necessary,most of the time it uses the lower voltage thereby keeping output transistor dissipation low.I hope this helps.
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Old 31st May 2003, 04:54 PM   #9
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Quote:
Originally posted by kevin gilmore
Ever seen a carver cube?

Works the same way.
Actually, the Carver M100 ("Cube Amp") was a class G design that used (I think) 3 rail voltages. I have also heard that the power supply, at least on the original models, wasn't up to par.

Bob Carver developed his patented Tracking Downconverter for his Sunfire products, after he left Carver Audio. I don't know if he brought the technology back to Carver when he returned.

It is my understanding that a Tracking Downconverter is a Class H supply.

Regards,

Mark Broker
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Old 31st May 2003, 05:13 PM   #10
sam9 is offline sam9  United States
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The weakness of all of these techniques seems to be that the switching activity itself introduces noise. However, in the last year or so, Doug Self published articlkes in Electronics World showing how, in at least one configuration, much of the noise can be reduced. One nice touch was that the inner (low power) outputs and rails can be operated as Class A without much penalty.

From a DIY standpoint, one of the more practical impediments is a tranformer with multiple voiltages. For instance to duplicate the rails (25V, 50V & 75V) of the M-400, one would need a transformer rated approximately 55-35-18-0-18-35-55. This is not something to be had "off the shelf". You could use thre separate transformers but that isn't going to be space efficient. I'm sure one could be custom made but I'll bet it would rndup 80%-90% of the total cost of the DIY project. There is a place where you buy the primary and a kit and instructions for winding your own secondaries. This might be useful for anyone who enjoys tedium.
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