Currnet Dumping Amps a review with pictures

[TLS Guy]

I posted last night on Seth=L's excellent thread posting the guts of amps.

I posted on the Quad 405, the first "Dumper" produced in 1975, with a link to Peter Walker's landmark paper in December 1975.

I also posted on the Quad 909 with pictures and circuit.

We are now 35 years on from the introduction of Current Dumping topology. Because of business practice and patent laws, the wider community has not benefited. I think if you look at these posts you will see why that is a tragedy.

 

[JerryLove]

So is there a specific part that is unavailable because of patent? If not, it would seem an enthusiast could build their own. How has the patent survived 35 years, I didn't think they lasted that long?

 

[TLS Guy]

So is there a specific part that is unavailable because of patent? If not, it would seem an enthusiast could build their own. How has the patent survived 35 years, I didn't think they lasted that long?

I'm not a patent lawyer.

Enthusiasts do build and tinker with current dumping amps. In fact if you search the NET you will find sites all over the world devoted to the mysteries and improvements of Peter's wonder. In fact they are among the most numerous sites in amp DIY audio.

However that does not solve the problem, of having the wider public reap the rewards. It should be possible to produce these amp about as cheaply or cheaper than class D and certainly cheaper than complex class AB amps. However IAG can, and do challenge anyone who uses the circuit or concept commercially. They would be far further ahead licensing it.

It is just a shame that after 35 years, this technology has been of benefit to so few comparatively speaking.

I have no idea how long you can hold on to a patent like this.

And by the way those amps are like silk, and as with all Peter's designs, unconditionally stable under all loads.

 

[JerryLove]

Went and looked it up:

1. U.S. Patents filed after June 8, 1995 expire 20 years from the date of filing.

2. U.S. Patents filed prior to June 8, 1995 expire 17 years from the date of issue, or 20 years from the first non-provisional patent application in the family - whichever is later.

I'm not a patent lawyer either, and I don't play one on TV; but it seems the patent on something from 1975 is clearly expired.

 

[highfigh]

I thought it was possible to renew patents.

 

[TLS Guy]

I thought it was possible to renew patents.

I have no idea. But US law is not the sole arbiter. The original patents are UK. So the patents have to expire in jurisdictions other than the US.

I know with drug, the companies try and play tricks with slight mods to extend patents. Fortunately when they try that the FDA ties them up is so much red tape they get nowhere.

Lets hope we are lucky enough to have a patent lawyer on the forums. We do have Kurt of BJC he likely would have insight.

If it is possible to produce this design commercial, it would be a great opportunity for say, Emotiva. I could not help noticing at SOTA the high part count compared to the Quads.

 

[sholling]

About the only way I know (not a lawyer) keep others from producing it is to patent refinements and then the new patents only cover the refinements. It's a sad but not that uncommon trait of inventors to fall in love with their idea and wind up making about 1% of what they would have made if they'd just licensed the technology and pocketed 3-5% of sales. Others sour on companies trying to steal their ideas and go hermit.

 

[TLS Guy]

About the only way I know (not a lawyer) keep others from producing it is to patent refinements and then the new patents only cover the refinements. It's a sad but not that uncommon trait of inventors to fall in love with their idea and wind up making about 1% of what they would have made if they'd just licensed the technology and pocketed 3-5% of sales. Others sour on companies trying to steal their ideas and go hermit.

1975 was a different era. Quad (The Acoustical manufacturing company) was a major manufacturer of audio equipment in the UK at that time. That was before the days of ridiculous pricing. The amps and FM tuners gave a steady income. They had to because they lost money on every ESL sold.

Peter never got to be a wealthy man out of designing and manufacturing audio equipment, but made a decent living.