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lumanauw 3rd February 2005 04:08 AM

What's the secret?


My patent 3,995,228 was submitted September 1975, and as far as I can see describes a circuit which would do either, but addresses Class A specifically. The basic circuit is similar to,
but predates the work of Cordell and separately, Hawksford.
They both obviously intended Class AB operation.

As an aside, I developed an extremely interesting circuit in
this area just as I was walking out the door at Threshold.
It remains a secret.
The last word is "secret". Anyone knows what it is?

JEKYLL 3rd February 2005 12:13 PM

If someone else that Mr PASS knows the secret then it's not a secret!

jacco vermeulen 3rd February 2005 04:25 PM

I'd say it is something Nelson Pass does not find interesting for his own purposes and does not see a reason why others should make a Dollar with.

I'd think he masters the art of knowing what not to tell, some say that is the wisest of all.

Nelson Pass 3rd February 2005 06:23 PM

I used to patent stuff, but that has gone to hell as a means
of protection. These days, if I want to preserve a design for
later use, trade secret becomes the practical method. When
it comes time to make a buck off it, my investment then goes
into the trade name, which is very easy to protect. :cool:

lumanauw 4th February 2005 12:40 AM


If someone else that Mr PASS knows the secret then it's not a secret!
:D Waw, it's true. Why I didn't think of that?

But here in passlab forum, people likes to draw cct from NP's words. X backengineered and XA backengineered are good examples.


OK, I'll give you a hint. The trick is to track and hold (for a while anyway) the minimum value of the sum of the currents throughthe positive and negative halves of the output stage. Regardlessof the dynamics of output current, this value is the bias, andcan be used to control an AB bias with great precision. There isa very cute circuit which uses a couple op amps tapped outsideof the signal path and not requiring an isolated supply which then drives an opto-isolated transistor in the bias circuit.

The decay time of the track and hold is set at a value lower than
the thermal time constant of the heat sinks and slower than the
audio signal.
I don't understand that. What's the drawing looks like?

lumanauw 4th February 2005 01:22 AM

Could it be the right side of LT1166?

GRollins 4th February 2005 01:29 AM

I put a little time into it and arrived at a partial solution. Then I got off-track, and since it wasn't relevant to anything I was working on at the time (I was approaching it simply as a puzzle) I dropped it and went on to other things. Then my hard drive crashed and the things I had scribbled about it got lost, including my e-mail back and forth with Nelson.
I remember (at least I think I remember) the first half of what I did, but will hold that seed in reserve until such time as Nelson chooses to release the idea. I've got a full plate right now, anyway. Desperately need to get a story out, and have four circuits going. All needing to be done yesterday, of course.


lumanauw 4th February 2005 02:10 AM

Mr. Pass,

I know a man with your caliber and loving for audio wouldn't just stand still in your "special area". Will study and look for anything related to audio amplification.

Have ever a ClassD variation includes in one of PassLabs "Hatfull of Ideas"?

I found some interesting variations can be made with classD.
-Labgruppen rail modulation
-Patent 5,612,646
-Patent 6,097,249
-Patent 5,657,219
That shows that one idea of ClassD can be made many-many clever variations.

Or you are still skeptical about classD?

Nelson Pass 4th February 2005 06:45 PM

Actually, at the moment I have a fan regulator that at least the
computer guys would die for. Works for audio, too.

Class D? I did once build a nice little Class D amp, a self oscillating
circuit that Gordon Holt said some nice things about. If you took
the cover off, you couldn't watch TV, though.

In case you haven't noticed, I like to work in the uncrowded
areas of design, so I don't do tubes (everybody and his cousin
has a tube design) and I don't do Bipolar AB designs (unless
you pay me big bucks) and I sell current source amplifiers for
little bitty full range drivers.

Class D amplifiers should theoretically attract some real
engineering talent, so they don't need me, do they?


jacco vermeulen 4th February 2005 08:36 PM

As the farmer said to the real engineer:
What do i need you for, you dont make money !

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