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Sound Quality Vs. Measurements
Sound Quality Vs. Measurements
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Old 6th February 2012, 08:48 PM   #1941
tvrgeek is offline tvrgeek  United States
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Speaking of clipping, I see a lot of effort to be sure amps clip nicely and recovery well. Sounds smart. I understand how feedback can be larger than one may expect. But, I have never seen any clamp on the input to keep stupidity from just overloading it in the first place. A good preamp can swing 8 to 10 volts, yet most (consumer) amps reach rated power with one to one and a half. I have no doubt there is a good reason, just have not seen it covered in the texts.
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Old 6th February 2012, 08:50 PM   #1942
bcarso is offline bcarso  United States
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Originally Posted by tvrgeek View Post
Jan just reminded everyone. The only absolutely correct, universal answer from any competent consultant is: "It depends." Treat all other answers as suspect.
Another one I like, in the same category as "this too shall pass":

"It's more complicated than that".

A maths friend of mine (Oxford PhD, studied with the late great dynamical systems theorist Vladimir Arnold) is quite amusing when he attempts to explain something. He once addressed a room of (mostly) engineers and some of us started to count how many times he said "basically". The final count for his short report on his group's activities was about 200.

You can never have too much math. But the "danger" is, it will become an end in itself and you will become a mathematician. And it's dangerous enough to start writing code, as one often becomes a programmer.

We take circuit theory often for granted, and suppose that it's wholly complete. Have you seen Paul Slepian's monograph? It takes the whole book to put resistive circuits on a rigorous mathematical foundation. No reactive elements let alone controlled sources, let alone anything nonlinear. I presume legions of grad students have extended the work since.

Anyway, somebody needs to design circuits.
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Old 6th February 2012, 08:54 PM   #1943
Wavebourn is offline Wavebourn  United States
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Sound Quality Vs. Measurements
Quote:
Originally Posted by tvrgeek View Post
Speaking of clipping, I see a lot of effort to be sure amps clip nicely and recovery well. Sounds smart. I understand how feedback can be larger than one may expect. But, I have never seen any clamp on the input to keep stupidity from just overloading it in the first place. A good preamp can swing 8 to 10 volts, yet most (consumer) amps reach rated power with one to one and a half. I have no doubt there is a good reason, just have not seen it covered in the texts.
I use optical limiters in my Pyramid amps. They sense current peaks of screen grids of output tubes and limit input signal level accordingly as soon as the amp approaches clipping.
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Nothing in the universe is perfect. The ideal things are the ones that are most optimal. Optimization criteria, what matters. When I hear "No Compromise Design", I want to take a sledgehammer and test how impact-proof it is.
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Old 6th February 2012, 08:56 PM   #1944
bcarso is offline bcarso  United States
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Originally Posted by tvrgeek View Post
Speaking of clipping, I see a lot of effort to be sure amps clip nicely and recovery well. Sounds smart. I understand how feedback can be larger than one may expect. But, I have never seen any clamp on the input to keep stupidity from just overloading it in the first place. A good preamp can swing 8 to 10 volts, yet most (consumer) amps reach rated power with one to one and a half. I have no doubt there is a good reason, just have not seen it covered in the texts.
Desigining a clean clipper is nontrivial. Although, I agree with you, the right place for it is in the signal domain (as opposed to further along when more power is involved). One recent article about phono preamps insisted that a preamp with a 36dB overload margin was needed. Well. Nice work if you can get it (if you make the gain low enough it gets easier, but that's cheating), but if you suppose that at normal decent listening levels you are running around 250mW average power and some healthy crest factor, where in the wide wide world of sports are you going to find a power amplifier that will cleanly reproduce a 36dB overload??

Brad
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Old 6th February 2012, 08:56 PM   #1945
Wavebourn is offline Wavebourn  United States
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Originally Posted by a.wayne View Post
No one could ever accuse you of wasting chassis material ......
It is called optimization.
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Old 6th February 2012, 09:07 PM   #1946
TheShaman is offline TheShaman  Europe
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"It depends" is great.
One of the first things our Cryptography teacher said back when I was doing my MSc.

Here's a handy one for those of us who're into (or have to...) write papers.

Sound Quality Vs. Measurements-407971_301726389875624_100001147953320_785970_925438643_n-jpg
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Old 6th February 2012, 09:10 PM   #1947
tvrgeek is offline tvrgeek  United States
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GOOTEE,
Yes, like ground but for power. I was thinking of splitting the DH-120 power as the input and VAS are fed after an additional RC filter on the rail, and the grounds are already separated on the board. Probably not the highest priority, but a thought.

Yea, subscribe. Did not know where they hid it.

Did not see Slepian. They have made it way to hard to get to the university library here. I can get a pass, but there is no parking. If he delved into what is actually happening at the quantum level, it could take several volumes and the final one would still be blank because we just don't really know. What I want to know, in use in a practical circuit, it is true that a half watt CF has about the same noise as a eighth watt MF but half the price? Seems to me this was suggested by none other than the Hafler company. Marketing or engineering?

"For any given product, there comes a time to shoot the engineers and start production"
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Old 6th February 2012, 09:15 PM   #1948
tvrgeek is offline tvrgeek  United States
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Another famous mathematician, also worked in cryptography, Tom Lehrer:

"When in doubt, plagiarize.
Let no ones work evade your eyes.
That's why God gave you eyes..."
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Old 6th February 2012, 10:49 PM   #1949
CopperTop is offline CopperTop  United Kingdom
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Originally Posted by TheShaman View Post
A good mathematician is good physicist and a good engineer. Sadly it doesn't go the other way around. If you can't see it you're probably an engineer.
I agree that mathematicians seem so clever that you might assume that they could easily do mere engineering without breaking sweat. I love the maths that can apparently model the real world, like reducing the bitrate of an audio signal inaudibly - suggesting that it really is some sort of model of the way nature, our brains and ears work.

But most people who profess to know maths... Don't they just apply and regurgitate standard formulae and techniques without necessarily knowing whether they are truly valid and applicable? I might like to think I know how to use maths to build a motor controller (or an audio amplifier...), but the maths ceases to be useful in the face of backlash, stiction and all the other nasties in the real world. A brilliant mathematician might blunder in, naively thinking he can solve such a simple problem in an afternoon, but the engineer would know it wasn't going to be so simple.

Engineering is about the messiness of the real world, sometimes on the level of gut feel, or dogged persistence and experience, where maths can't help you.

As an aside, I'm fascinated by the idea of self-learning systems that can simply bypass the need to learn certain types of maths - and then be disappointed to find the maths was so 'naive' it didn't solve the problem anyway! (You always end up twiddling the 'pots' manually on your PID controller or phase locked loop, seeking speed of response with stability, even if you went by the book when designing it).

Here's an example where a mathematician couldn't have helped you to solve a real world problem, but where there was an empirical solution (captured by use of a self-learning 'black box'):

Quote:
Neural networks can be used to solve highly nonlinear control problems. A two-layer neural network containing 26 adaptive neural elements has learned to back up a computer-simulated trailer truck to a loading dock, even when initially jackknifed. It is not yet known how to design a controller to perform this steering task. Nevertheless, the neural net was able to learn of its own accord to do this, regardless of initial conditions.
IEEE Xplore - The truck backer-upper: an example of self-learning in neural networks
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Old 7th February 2012, 12:22 AM   #1950
gootee is offline gootee  United States
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Quote:
Originally Posted by TheShaman
A good mathematician is good physicist and a good engineer. Sadly it doesn't go the other way around. If you can't see it you're probably an engineer.
This might be true when they are infants. But after working in one field or the other and gaining experience and "the mindset", they are usually no longer able to do each other's job, very well. It doesn't go EITHER way, easily.

But, if need be, an engineer could probably fill the others' shoes better than they could fill his, because while many engineers are extremely good at math and physics, the engineer's job (in many cases) also has non-math and non-science components that are absolutely critical to success, mainly consisting of juggling cost, schedule, and (product) performance, and the many risks that affect them all. Any mathematician or physicist who also does that, or is good at it, IS an engineer, also.

(Edit: ) The more I think about it, the more I think that the OP had it exactly backwards.

Last edited by gootee; 7th February 2012 at 12:29 AM.
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