Class D (PWM) amplifier archaeology

[mhardy6647]

So, I'm a scientist, not a historian, but I am still fascinated by history... and I crave context.
You all know that the late Sir Clive Sinclair is regarded as the purveyor of the first significant PWM amplifier products for audio.

Sinclair X10 class D biased amplifier. - UK Vintage Radio Repair and Restoration Discussion Forum

Sinclair X10 class D biased amplifier. Vintage Audio (record players, hi-fi etc)

www.vintage-radio.net

A whole book on Sir Clive in (?) the public domain: https://worldradiohistory.com/BOOKS...inclair/The-Sinclair-Story-Clive-Sinclair.pdf

Bruno Putzeys article

I was reading about the origins of Class D amplification earlier and came across this interesting article from 2008.

forum.polkaudio.com

Here at ASR, and at other forums, there are snippets of information about the early history of pulse width modulation for audio amplification. @SIY here, e.g., has pointed "us" (me) in the direction of some of the earliest publications on the subject.

For whatever reason (avoiding actual work, most likely), yesterday I decided to go a-sleuthing for the earliest information I could find, using the breadcrumbs dropped by @SIY as my guide.
Needless to say, https://worldradiohistory.com/ played a key role in enabling this flight of fancy! I love that site.

I struck pay dirt, too!
This may be of no interest to anyone but me, but I decided to post the fruits of my labors in its very own thread! So, here you go, as-is, and FWIW. No warranty express(ed) or implied. YMMV. Yadda^3.

A triumvirate of early pubbies from Audio.

George Fletcher Cooper
https://worldradiohistory.com/Archive-All-Audio/Archive-Audio/60s/Audio-1963-06.pdf pg 24
https://worldradiohistory.com/Archive-All-Audio/Archive-Audio/60s/Audio-1963-07.pdf pg 24
https://worldradiohistory.com/Archive-All-Audio/Archive-Audio/60s/Audio-1963-08.pdf pg 23

Then, I think, the article(s) by Norman Crowhurst that @SIY alluded to.
A four-parter.

source: https://worldradiohistory.com/hd2/IDX-Audio/Archive-Audio-IDX/IDX/60s/Audio-1965-08-OCR-Page-0004.pdf#search=%22crowhurst%20pulse%22

Norman Crowhurst
https://worldradiohistory.com/Archive-All-Audio/Archive-Audio/60s/Audio-1965-09.pdf pg 19
https://worldradiohistory.com/Archive-All-Audio/Archive-Audio/60s/Audio-1965-10.pdf pg 32
https://worldradiohistory.com/Archive-All-Audio/Archive-Audio/60s/Audio-1965-11.pdf pg 36
https://worldradiohistory.com/Archive-All-Audio/Archive-Audio/60s/Audio-1965-12.pdf pg 36

Finally, a much more modern historical overview that incudes references.

Quick historical overview with refs.
https://worldradiohistory.com/Archive-All-Audio/Archive-Studio-Sound/80s/Studio-Sound-1989-02.pdf pg 60 & 62

I hope this is of some interest to someone (I mean... you know... besides me).

 

[fpitas]

Thanks! Like some other notable methods that were highly desirable from an engineering viewpoint but impractical in the past, such as switching power supplies and high-bypass turbofan jet engines, the idea has floated around a very long time.

 

[mhardy6647]

A couple more vintage articles.
This one's mentioned at the Polk forum post cited above.

https://worldradiohistory.com/Archive-Radio-Electronics/60s/1967/Radio-Electronics-1967-09.pdf pg. 72

... and one from Leonard Feldman, also in Radio Electronics, from 1977.

https://worldradiohistory.com/Archive-Radio-Electronics/70s/1977/Radio-Electronics-1977-09.pdf pg. 59

 

[Chrispy]

Same Sinclair as the computers, yes? I knew about those, but not the amps. Thanks.

 

[fpitas]

It's a miracle they got those old germanium transistors to work as well as they did.

 

[pma]

I made a system for analog signal transmission through optical fibre, based on PWM, in 1982 and published it in 1984

https://pmacura.cz/img456_ST_6_1984.pdf

The carrier frequency was 170kHz, bandwidth 0 - 17kHz/-3dB, S/N = 54dB. It was used for measuring purposes during high voltage tests of power circuit breakers, however could transfer the audio signal as well .

 

[mhardy6647]

Same Sinclair as the computers, yes? I knew about those, but not the amps. Thanks.

yes, the very same. Clive Sinclair presaged (or at least was on the leading edge) of myriad tech trends.

Check out the book in the link

 

[fpitas]

Unfortunately, he didn't realize that class D can never be audiophile

 

[Doodski]

Wowzer in 1965 a PWM design audio amp and hardware to go with that too.

 

[GXAlan]

@pma with your SA-600 simulation nicely matching the measured performance, can you simulate this Class D amp from the same time?

 

[pma]

@pma with your SA-600 simulation nicely matching the measured performance, can you simulate this Class D amp from the same time?

Wow, you mean the X-20? I may have a look at it. It is more difficult than to simulate a linear amplifier. I already tried to simulate the UcD, some time ago.

 

[GXAlan]

Yeah, I was thinking about the X-20. I wonder if if that would be 40 dB sinad or if it gets to 80 dB

 

[pma]

Rather 40-50dB, than 80dB.

 

[tjf]

As long as we're looking at early Class D implementaions....The Infinity SwAmp amplifier from late 70's I think?

From John Ulrick -- later to start Spectron -- makers of Class D amps...

Infinity DSP on thevintageknob.org

vintage Infinity 1976 Class D amplifier - with some Sony in it.

www.thevintageknob.org