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Old 15th October 2005, 03:28 PM   #1
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Question X/SuperSymmetry - Am I Missing Something?

I've been looking at Pass' X/SuperSymmetry amplifier stuff, wondering what the patent is actually for. (I've even looked at the patent!) So far, I haven't found it. But, just in case I've overlooked it, I thought I'd ask here: what am I missing?

Here's my understanding of it so far.

The amps in question are basically differential-input, differential-output amps, with some kind of long-tailed pair (or simple variation thereof) for the inputs. And negative feedback is applied from the outputs to the inputs, by feeding each output back to the corresponding, inverting (relative to that output) input.

That seems to be it.

So, what's the patent actually for? What have I missed? Surely the patent can't be for what I've described (in summary) above. (Then again, given the reputation of the US PTO...)

?
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Old 15th October 2005, 04:00 PM   #2
flg is offline flg  United States
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I felt like you do, and I would still admit, I am not the one but... 1st, The normal diff pair does not use the F.B.. Due to the feedback though, any "output" signals appearing at the gates form some gain controled signal "processing". The signals at the gates are level shifted to the Sources and hence transfered to the other Source and level shifted to it's gate. At the same polarity that it showed up at the first gate... Therefore, these signals can possibly appear common mode and not be "processed" (amplified). Distortion appearing at the first drain and being feedback to the gate is not the same as music being summed at that point with the feedback. Therfore it is possible to "process" the input signals and treat the distortion like a common mode un processed signal. Nelson say's an order of magnatude I beleive better distortion figures... Wow, I will now wonder if I have made a total something of myself or maybe someone will help me out...

Thanks
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Old 15th October 2005, 06:48 PM   #3
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Quote:
Originally posted by flg
I felt like you do, and I would still admit, I am not the one but...
Thanks, but I already knew that that's how they work. It's just what long-tail-pair-style inputs do. And when negative feedback is applied to each (inverting) side? Why, it still does that - quelle surprise!

Let me put it another way.

Imagine you've got an op-amp with differential outputs. Being an op-amp, it's also got differential inputs. Suppose, also, that the outputs have a bit of distortion. Now, if you were to apply feedback to reduce that distortion, how would you do it? (Note that the inputs and outputs are both differential, which means that either input can be regarded as inverting, depending on which output you choose to regard as non-inverting )

How would I do it? Well, I'd probably stick feedback resistors between the outputs and the inputs, and add some input resistors, too. The inverting input would be connected, by a feedback resistor, to the non-inverting output, and the non-inverting input would be connected, also by a feedback resistor, to the inverting output. The two feedback resistors would be the same as each other, as would the input resistors.

Does that seem reasonable? Does that seem, perhaps, obvious and trivial (once you understand what a differential-output op-amp is)?

Now, suppose, internally, the op-amp just happens to have a long-tail-pair-style input?



What of Pass' patent now? How is it not a patent on the trivial, the obvious, the old-as-the-hills?

What am I missing?
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Old 15th October 2005, 09:02 PM   #4
Netlist is offline Netlist  Belgium
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Did you look at the article at passlabs?
There you will also find the patent # in case you want to understand the full details.

/Hugo
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Old 15th October 2005, 09:19 PM   #5
flg is offline flg  United States
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Not knowing what is actually in your diff opamp, I would only repeat, I'm not such a good teacher. But, If you have read the patent, I believe the description covers what this acrticle also covers regarding typical opamp configurations... It may not address your particular idea ... Using an opamp to acheive a similar topology would likely be outside the scope of the patent ...

http://www.passlabs.com/downloads/articles/susy.pdf

This should explain why typical circuits are not symetrically canceling with balanced and opposite signals... vs just using feedbak... It is not meant to be anything complicated... Just very usefull... And patentable...
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Old 15th October 2005, 09:31 PM   #6
forr is offline forr  France
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The patent for super-symmetry is super-mystery.

~~~~~~~ Forr

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Old 16th October 2005, 04:16 AM   #7
azira is offline azira  United States
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well... I'm sure this'll be far from exact but let me take a stab at this.

First, IMO a patent serves two purposes.
1) allows the owner exclusive rights to license or produce the particular technology for 10 years.
2) claims the owner as the inventor of the technology.

Now, obviously #2 is important to the petitioner but #1 is the important one.

The truth is, you're right, and there are plenty of patents out there that seem obvious or "duh". But lots of times it's only obvious after the fact that the obviousness comes out and the point really is: the patent was specific enough to get approved.

So if you look at the patent for X/SuSy, yeah it's negative feedback, but it only works for perfectly matched pairs, and the patent is specifically for cascoded LTPs with the feedback taken from the LTP, not after a VAS. And that's a pretty specific criteria. That's why it's patentable. If you were to apply X feedback to a Cascoded matched LTP with a say... a matched Source follower after it, well that'd be a different circuit and you could most likely market it (as long as your lawyer is better than NPs )
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Old 16th October 2005, 07:32 AM   #8
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Quote:
Originally posted by Netlist
Did you look at the article at passlabs?
There you will also find the patent # in case you want to understand the full details.
Yes, I've read that article, and (as I mentioned) had a look at the patent.

I also had a bit of a search through this forum, too.

And I've also had a brief look at the SuperSymmetric Son of Zen thing on (what was it?) PassDIY (or whatever it's called).

Perhaps I should spell it out: I have no difficulty seeing how distortion on one output ends up on the other output, such that it differentially reduces that distortion.
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Old 16th October 2005, 07:53 AM   #9
Netlist is offline Netlist  Belgium
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The nice thing about this topology is that many people seem to implement a lot of variants. From extremely simple (which most of us like) to more complex schematics have arisen all over the passlabs forum. I'm not sure if an x-tube amp has been done but I'm sure it must be perfectly possible.

/Hugo
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Old 16th October 2005, 11:55 AM   #10
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Well, its easy to say all the words now. We have look at all the schematics, the smart tricks, from all over the smart brains all over this world, and say what's so special about it, because it makes sense and it is just the way to achieve the targetted result, many else uses that same trick, it is the only way to do it, etc...etc....etc.....

But imagine when you have no, or much less schematics to study, what year is that patent? Is internet already available in that year? And you come with that idea from yourself, resulting something special result, will you think "Ah, I will not patent it, although I make amps for my living"?

You should see patent #6.882.225, it is dated 10 April 2005, is he inventing something not known before 2005? Why do you think he make the patent, cost so much?
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