Can I sell amplifier modules which were designed by someone else ? - diyAudio
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Old 4th September 2014, 08:39 PM   #1
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Default Can I sell amplifier modules which were designed by someone else ?

I have taken an old Maplin design (JL Hood original design) and updated all the transistors in it to modern equivalents or better but left the circuit the same.
Is it OK to sell these amplifier modules ?
The designer passed away in 2004.
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Old 4th September 2014, 09:57 PM   #2
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Patents in the U.S. run out after I think 17 years, in case the circuit was actually patented. Not sure how the law works in other countries or outside of the country or origin. Updating the transistors is likely to change the phase margin (tendency to ring or oscillate) if there's any negative feedback, so I'd take a close look at how cleanly it goes in and out of clipping with a 10kHZ squarewave signal at least.
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Old 4th September 2014, 10:01 PM   #3
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The circuit was used by Maplin electronics up until about 1990.
The circuit has been published in their magazine with no references to copyright.

I had a look at the output on a scope with music and it looked very clean.
I will give the square wave test a go and see how it performs.
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Old 4th September 2014, 10:13 PM   #4
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Quote:
Originally Posted by nigelwright7557 View Post
The circuit was used by Maplin electronics up until about 1990.
The circuit has been published in their magazine with no references to copyright.

I had a look at the output on a scope with music and it looked very clean.
I will give the square wave test a go and see how it performs.
The WHOLE Magazine is copyright

And it states so somewhere .

Even if not, it's implicit.

Clear it with Maplin or the Magazine editors first.

EDIT: the University of Cambridge states:

http://www.caret.cam.ac.uk/copyright/Page171.html

that even for "unknown Author", copyright holds for 70 years from date of publishing.
Quote:
University of Cambridge Home

Home > 4. Detailed information on copyright and intellectual property rights > 4.3 Duration of copyright >

Works of unknown authorship

70 years from the end of the calendar year in which the work is made. However, if the work is made available to the public during that time then copyright expires 70 years from the end of the calendar year in which it is first made publicly available.

Last edited by JMFahey; 4th September 2014 at 10:20 PM.
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Old 4th September 2014, 10:21 PM   #5
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I have already copied the Maplin 150WRMS MOSFET amplifier but I know that isnt copyrighted. It is from a Hitachi datasheet for lateral mosfets.
I changed the design for vertical mosfets.

I have contacted Maplin in regards to the 50WRMS amplifier.
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Old 4th September 2014, 10:33 PM   #6
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Originally Posted by JMFahey View Post
The WHOLE Magazine is copyright
.
The magazine article referring to this amplifier is also on the internet.
50W HiFi Power Amplifier LW35Q Maplin Kit
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Old 4th September 2014, 10:51 PM   #7
jcx is online now jcx  United States
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copyright doesn't protect circuits - only drawings, manuals, articles, pcb artwork

but the circuit topology, even implemented with the exact same part #s isn't protected by copyright if you lay out your own board, provide your own documentation


in Europe 20 years is the standard for patent protection, the US has changed to match

anything sold, derived from patents and publications older than 20 years are "prior art" - any circuit idea published over 1 year ago is also public domain unless the inventor has applied for a patent - even if the article gets copyright protection - the idea doesn't
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Old 4th September 2014, 10:56 PM   #8
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I have used a complete set of different more modern transistors.
I have also laid out my own PCB which is quite different from the original.
Some of the circuit component values have been changed.
I also added a capacitor to the circuit.
The circuit part numbers have completely changed. The pcb was re-annotated so the components numbers flow from the top of the pcb downwards.

The topology is LTP, VAS, Vbe multiplier, driver stage then output stage.
This is quite a common topology.
The only unusual stage is the output stage which is common emitter.
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Last edited by nigelwright7557; 4th September 2014 at 11:03 PM.
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Old 5th September 2014, 12:37 AM   #9
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I agree with the comments above. I wouldn't call it a Maplin anymore though. Call it a derivative if you want to make reference to the original version. With higher speed parts it becomes more important to have good power supply bypassing right in the circuit area. I'd use 0.1uF caps across 100uF AE caps on each rail to Gnd..
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Old 5th September 2014, 12:45 AM   #10
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Quote:
Originally Posted by Bob Richards View Post
I agree with the comments above. I wouldn't call it a Maplin anymore though. Call it a derivative if you want to make reference to the original version. With higher speed parts it becomes more important to have good power supply bypassing right in the circuit area. I'd use 0.1uF caps across 100uF AE caps on each rail to Gnd..
One of the changes was using 470uF across power rails.
I didn't add 0.1uf though. Might do that on next revision.

It is originally a John Lyndsey Hood design.
Sadly John passed away in 2004.
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