On topic for a change 
EDN just published Part 2 of Bruno Putzey's article The F-word - or why there is no such thing as too much feedback.
jan
EDN just published Part 2 of Bruno Putzey's article The F-word - or why there is no such thing as too much feedback.
jan
(If one of these has escaped your attention…)
George
Come on George this is real DIY, mailing tube and sheet plastic and a re-purposed cheap computer speaker.
The only neat trick is a medical grade pressure guage reference (of course re-purposed from a CPAP machine). Translated to audio they have to be trimmed to .1dB absolute "SPL" at DC and happen to have response to 3K or so.I have yet to compare it but we do have some capsules calibrated by B&K to some ridiculous level.
I make a hi-Q resonant chamber at 350Hz or so and can get up to 150dB SPL inside in an ear safe fashion. The transducer is flat out to 3500Hz or so so the error at 350Hz from DC is small.
The Q is air/speaker compliance and mass since the chamber is much smaller than a wavelength. The speaker actually hardly moves and since the resonance is not wavelength derived the harmonic rejection is good. I was amazed to see -60dB on a good 1/2" mic. at modest levels. The pressure transducer is from GE NovaSensor and is the same one Jim Williams used to make a barometer application. I simply use it to sample the internal pressure near the mic. Yes I'm sure there are details the need attending to at the 1dB level but it looks promising. It makes a pretty bad mic (about 15uV/PA) so I use one of our in-amps at high gain set by reading the value of the transducers internal laser trimmed gain resistor and selecting the right value. In this way I preserve the specified 1% (.1dB) specification.
The mics (omni only obviously) are inserted through a grommet lined hole, and the tube of the pressure guage next to it. It is very important not to let outside leakage contaminate the guage (reference) tube. There is no point finalizing the project until I compare it to a known reference. The mics that we used at SY's party measured exactly their specified 10mV/PA.
In any case it is useful for driving mics to clipping and observing any bad behavior comfortably at your bench. I used this for my article to make sure none of the circuits behaved miserably. Also relative matching of capsules should be easy.
I have seen the pressure guage for as little as $17 but I think it is well stocked at $35 in ones at several distributors. The AC performance is not specified I just found it empirically.
That's funny in a way, although also absurd and I suppose actionable. You probably should notify the seller and eBay and complain.
Do you remember when Nak licensed Nelson's Stasis patent for a power amplifier? That makes his connection a bit more plausible at least, but perhaps it is also a misattribution.
Oddly, a guy who worked for Niro Nakamichi displaced me a few years ago from assignments with a client I didn't much mind losing, as the company owner had an uncanny knack for betting on the wrong horse as it were, and as well the environment was rather a bad soap opera with intrigues, spoils, and stratagems. And the really irritating thing was, although they did pay me, with one exception anything I did for the company never got built. The one thing that did, a ten-pounds-in-the-proverbial five pound bag device, was fabricated with an abundance of errors in layout and at the last minute, with the layout guy expecting me to fix all of his mistakes (in mostly SMD parts) in order to prove that the circuit worked
. When I designed a handheld device for determining the thickness of possible body filler like Bondo over damaged ferromagnetic auto bodies, that got built and worked like a charm, but I was paid by the customer of the company.
Ebay is hardly without sin, but if it were their listing, they'd probably do something about it. They seem to actually be trying to keep the reigns on things, bless 'em.
Nakamichi of that era used an interesting power supply variant that deserves more popularity: they had supply decouplers with a simple pass (NPI) device whose base was connected to a Zener that then, instead of connection to signal ground, was connected to the source (or sometimes the emitter) of a follower whose drain (or collector) came from the opposite polarity supply, and whose gate (or base) connected to signal ground. Local signal ground stayed a little less contaminated by the machinations of the decouplers.
Thanks,
Chris
Nakamichi of that era used an interesting power supply variant that deserves more popularity: they had supply decouplers with a simple pass (NPI) device whose base was connected to a Zener that then, instead of connection to signal ground, was connected to the source (or sometimes the emitter) of a follower whose drain (or collector) came from the opposite polarity supply, and whose gate (or base) connected to signal ground. Local signal ground stayed a little less contaminated by the machinations of the decouplers.
Thanks,
Chris
Amusing story. I did not design their preamp stuff either, but I did license
an amplifier patent to them. Niro was still nominally in charge at that time
and I enjoyed meeting him.
There were some people there with egos as large as mine, and they sold
lots of product, but in the end it doesn't seem to have sustained itself.
However, they did put Toshiba Jfets in their phono stage...
an amplifier patent to them. Niro was still nominally in charge at that time
and I enjoyed meeting him.
There were some people there with egos as large as mine, and they sold
lots of product, but in the end it doesn't seem to have sustained itself.
However, they did put Toshiba Jfets in their phono stage...
Sorry just noticed that it was audiogon. My apologies to eBay (and Radio Shack).
Well you can't go too far wrong with thoseHowever, they did put Toshiba Jfets in their phono stage...
Nelson and I were mentioned, because we are both known to be 'world-class' audio designers. That means that at least some of our designs are noted as 'best of its kind' by 'third party' institutions.
This does not come from 'luck', it doesn't necessarily come from education, (although it helps) but, in my opinion: Intuition and Experience.
This is why new college graduates often fall flat when designing 'successful' audio electronics. The arrogance given to the new graduate from knowing a lot of extra math, perhaps more than 99.9% of the general population, and following the philosophy of the 'skeptics' of elegant audio design, may give the new engineers a design that measures well enough, BUT will probably never be really successful, especially over a long period of time.
Stick with servos and test equipment, guys! '-)
This does not come from 'luck', it doesn't necessarily come from education, (although it helps) but, in my opinion: Intuition and Experience.
This is why new college graduates often fall flat when designing 'successful' audio electronics. The arrogance given to the new graduate from knowing a lot of extra math, perhaps more than 99.9% of the general population, and following the philosophy of the 'skeptics' of elegant audio design, may give the new engineers a design that measures well enough, BUT will probably never be really successful, especially over a long period of time.
Stick with servos and test equipment, guys! '-)
Yes John - there are a lot of designs that maybe are technically "perfect" and done by the "book" that will never sound good
I don't know any new college graduates who can design their way out of a proverbial audio paper bag. If they are arrogant because of extra math they don't seem to display it (arrogance perhaps, but maths no). More likely they paste together app notes and "pray" a lot --- if, to begin with, they are hired and given that level of responsibility.
Yes intuition and experience are crucial in most electronics. What we used to have were people who started playing with electronics in their teens, and acquired some feeling for signals and systems, perhaps developing theories and rules-of-thumb that might be in error at some level, but at least were linked first-hand to experience. If they were interested enough to pursue science and engineering going forward, they had a leg up on the material and could see its utility. This pretty much ended in the late '60s from what I could see.
Another factor in the restriction of the breadth in skill sets and creativity was the big drum beaters for "digital" supposedly taking over everything. I had a respected transducer/speaker designer tell me that there was nothing left for me to do outside of digital --- this in 1997! I told him that every time I heard a statement like that, I knew I'd have work for the foreseeable future.
But there was, and perhaps continues to be, a rationale for BS degree folks to focus on digital, especially just programming, because it is so simple. There is a chance for you to get good-enough at it to get a job fresh out of school and actually contribute. Otherwise you will have to have had the background for years preceding your formal education, or be furiously bright and quick to absorb things, or have a series of especially outstanding teachers of analog electronics, to have a chance of being useful upon graduation.
A wonderfully bright and well-rounded applications guy who left us far too soon, Jim Williams, I believe had essentially no formal engineering education at all, but did fantastic work, and his departure has left a gaping hole at Linear Technology. I didn't know how serious this was until talking to someone recently, who said there seems to be no one there anymore to help him. I'm sure to some extent this is an exaggeration, but maybe not too much of one.
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