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Old 17th November 2004, 01:47 AM   #1
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Default Class TD reversed engineering possible?

A pro audio manufacturer (Labgruppen) have a very smart way to make efficiency with power supply. It's similiar to classH, where the voltage is always maintained +/-5V above and below the output signal, but this is done with PWM+buck regulator, not with analog dissipation like classic class H.

Anyone can help with making DIY version of this idea? My own idea is that I have to make 3 power amps. One is the main power amp for audio. The 2nd power amp is classD for making modulated +rail supply and the 3rd is classD for making modulated -rail supply.

How to make a classD power amp, that always give +5V more than the output signal for +rail, in the exact phase always to the output audio signal? And the other for making -5V for negative rail?

But a question arrises. Does the classD power amp can have exactly delay time compared to any power amp? If not the supply track and the audio track will be in the wrong phase.
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Old 17th November 2004, 02:09 AM   #2
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This is what I want to achieve.
Trace B is output audio signal. Trace A is modulated +supply that is always +5V than the output signal (but needs to very sure that it always in phase with B). This A is made by classD. C is the same as A, made by another classD always -5V than B.

The supply rail is very high like +/-120VDC, but with this trick, the power amp B will be working lightly, only from +/-5V supply. The rest of the burden is taken by amp A and C which is classD, efficient.

One may ask, why not making a direct classD amp? Well, this idea is tobe implemented in an existing power amp, any power amp.
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Old 8th February 2005, 01:43 PM   #3
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Isn't that what the "Tracking Downconverter" does in Sunfire amps? I thought that was Carver patented stuff.

He's been working for years to make it work... He's seen a lot of smoke working on that one.

His voltage is always 6V above output. Check this:

Tracking Downconverter Sunfire

The bad thing here is that the slew rate is almost tube like (in the first designs anyway)
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Old 8th February 2005, 05:19 PM   #4
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Hi,

Here is Carver Corporation patent describing requested technology. On the other hand, if you do your tracking converters well enough, you end up with a class D amplifier.

The patent is interesting because it uses active damping of LC filter resonance which can also be applied in any class D amplifier. I have not seen that mentioned anywhere before.

Best regards,

Jaka Racman
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Old 9th February 2005, 07:34 AM   #5
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Quote:
Originally posted by Jaka Racman
Hi, Here is Carver Corporation patent describing requested technology. On the other hand, if you do your tracking converters well enough, you end up with a class D amplifier.

The patent is interesting because it uses active damping of LC filter resonance which can also be applied in any class D amplifier. I have not seen that mentioned anywhere before.
Rob Williamson (the patent holder) was a friend of mine. I am sad to report that he died quite suddenly and unexpectedly several years ago much too soon (in his early fifties). He, I and another friend had many a late night kitchen table discussion at my house about feedback schemes. Active damping has been occationally used in switching power supplies before Rob's patent. Our discussions on such subjects were the spark that lighted the way to the formulation of my generalized leap frog design method (it can be looked at as active damping for an arbitrary number of filter elements). -- analogspiceman
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Old 9th February 2005, 07:36 AM   #6
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Analogman,

So you must have know Mr. Carver himself as well then?
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Old 9th February 2005, 07:51 AM   #7
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Quote:
Originally posted by Yves Smolders
Analogman,

So you must have know Mr. Carver himself as well then?
Not really, but I have worked with quite a few people who have worked with him. From all accounts he is more snake oil salesman and yarn spinner than knowledgeable engineer (when it comes to succeeding in the audio business, the former attributes are perhaps more important than the latter, unfortunately). I worked for a time at the Carver Corporation designing a class d amplifier, but it was after the board had kicked Carver out of his own company because he was so hard to get along with. He had the last laugh, though - without his marketing charisma the company went bankrupt and he eventually bought his name back for a song. -- analogspiceman
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Old 9th February 2005, 10:14 AM   #8
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Is it possible to do such thing without opamp or comparator (only with small number discrete components, choke, mosfets, caps, diodes)?
I'm afraid about the phase shift from the original audio signal, especially in high frequencies, or when headed to reactive load.
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Old 9th February 2005, 07:45 PM   #9
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Hi analog,

thanks for the interesting (and sad) story. Now I understand your familiarity with active damping which seems to be one of the best keept secrets in SMPS and classD industry, especially when all that is required is ultimately only one feedback cap from the output filter cap to the input of the PWM comparator. I would say that even UcD profits from that.

Lumanauw,

I suggest you look at the UcD amplifier discussed in this forum. It has a single pole rolloff and 35kHz power bandwidth, so it could be compatible with linear amplifier possessing similar caracteristics. It has completely discrete modulator so you might get some ideas.

Best regards,

Jaka Racman
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Old 10th February 2005, 03:11 AM   #10
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If audio amp is one amp, does making this idea is the same as making 3 amps? One for audio itself, one for plus rail and one for negative rail?
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