Steve Ohr is continually amazed by the diversity of the feedback he gets from his personal blogs and columns — as well as those of other Planet Analog contributors. In one case, Ohr angered audio component vendors who felt he was being unfairly negative toward Class D amplifiers. In another editorial, this one about the acceptable responses to terrorism, Ohr triggered a lengthy "means-vs.-ends" discussion — as well as number of personal recollections from readers. Here is a little sa
Remember how we promoted Bill Klein's column on "Thermal Gradients"?
"Op amp circuit troubleshooter Bill Klein was asked to solve an oscillation problem. He instinctively wondered about power supply coupling, until his caller said the blip was 2 seconds on, 2 seconds off, and he could smell something burning. Read about "A Call I took Last Week
Norman Dancer, a Bay Area engineer (Member of the Technical Staff) shared this recollection with us:
"Now I can't vouch for this story because I never took one apart, but I was told, early in my career, that the venerable LM309K 5 volt regulator (a Bob Widlar circuit if memory serves) was used to replace relays in those yellow flashers you see at road construction sites. The circuit was simple - a 12 volt battery, a five volt bulb, and a 309 without a heat sink. That little doodadie would turn on, heat up to thermal limit, then shut down, thereby initiating and maintaining flashing. At the time I was told, 'Yes, it exceeds the recommended operating temperature of the device, but the reliability is about five times that of the relay.'
"As I said, this was a long time ago - in the sixties, no less, but...
"As an aside, whenever a circuit that should have a quiescent point of, say, three volts, and it's always away from there, putting your finger next to it can sometimes change the voltage even though you don't touch it! The effect is that the device is oscillating with stray capacitance as part of the feedback, and your finger changes the capacitance and hence, the resonant point.
"By the way, even though I do do thermal analysis, there's what's known in the industry as 'Norm's rule of thumb!' If I can keep my thumb on it, it doesn't need a heat sink!"
The truth about Class D amplifiers: a manufacturer protests
Kevin Belnap took exception to Steve Ohr’s May 9th column
in EE Times, and Planet Analog invited his response. Ohr is exaggerating Class D’s distortion characteristics, Belnap says
. Class D can appeal to audiophiles and listening demonstrations at CES have proven that.
Kevin's article (and Ohr's footnote to that) generated responses from audio equipment and components suppliers who felt he was being unnecessarily harsh, and from those who understood his remarks not as a blanket condemnation but as a cautionary reference.
Marcel Croese of Creato Audio in Utrecht, Netherlands writes:
"I also was slightly upset by Steve Ohr's 'truth' about Class D amplifiers. As an engineer specialized in implementing several of Philips's UCD class-D solutions into true audiophile's environments (audiophile in the sense of 'equipment fit for customers that have very high demands of quality sound reproduction') I have hard data on our solutions that prove that distortion figures of well-implemented class-D technologies can remain below 0.005% THD at any frequency within two octaves beyond the audio band (either way) at either power output until full rated power.
"I would strongly urge the respected Mr. Steve Ohr to differentiate very meticulously between SOUND IMPLEMENTATIONS of well-designed class-D modules on one side and RANDOM (data sheet based) implementations that are destined for flat-panel TV and/or el-cheapo surround amplifiers/receivers on the other. The latter explicitly NOT representing ANY inherent quality of class-D save for power efficiency and decreased space occupation compared to good old class AB.
"But well-implemented class-D will blow your socks off in any contest between old and new (class-D vs. class AB) and truly show why it is rapidly becoming the audiophile reality that it deserves to be."
Gordon Jacobs in Oakland, California writes:
"Kevin Belnap's response in the July 21 issue to an earlier article critical of Class-D amplifier specs itself makes a unrealistic representation, by stating that his T.I. parts are 'targeted to DVD receivers that are typically rated at 10 percent THD+N'. The T.I. parts may indeed target Receivers that rate their power at the 10% distortion mark, but a simple survey of most common A/V Receivers on the market shows that they typically quote rated power at THD+N figures of less than 0.1%. He then goes on to discuss clipping as a source of distortion, but it is not clear what the distortion mechanism is in the response curves presented. The measured curves show distortion rising dramatically well before the rated power. As such, a user of the parts would be likely to rate their product below the T.I. rated power or suffer in the marketplace with highly inferior distortion specifications. Class D amplifiers have improved greatly and they are suitable for many applications. But the response from T.I. looks more like an effort to adjust the specifications to match the technology (backwards) than designing technology to match required specifications. Perhaps Kevin should try another approach and compare Class D specs with those of vacuum tube amplifiers, which are known to possess higher distortion but have a wonderfully 'warm' audio sound!"
And Tranh Nguyen, Chairman and CTO of NPhysics, Inc. writes
"Dear Mr. Ohr, I missed your latest article on class-D amplifiers but just read Kevin Belnap’s guest commentary in the July 18, 2005 issue of Planet Analog. Your footnote comment still voices the doubt about current class-D implementation’s audiophile quality.
"Please doubt no more, Mr. Ohr. You can first go to our web site www.nuforce.com and read about our class-D amplifier technology, and many links to reviews by a couple of audiophile magazines and by many end users. Five more international reviews are also coming out any time soon. Then you can go to www.Audiocircle.com and the likes, and search for postings on our NuForce Reference 8 amplifier. The NuForce threads happen to be the most viewed on Audiocircle.com.
"Then for your ultimate opinion, we invite you to audition an audiophile system powered by our NuForce Reference 8 amplifiers for what many consider as the ultimate audio experience in their own audiophile system. We currently have dealers and distributorships in some 20 countries in the world.
"You need to be informed of the tremendous progress we have been making in class-D, with a series of patents and pending patents."
The only sane response to terror is simply to carry on
After the terror attacks of 9/11, New York City's Mayor Rudolph Giuliani's was saying things like: "Go shopping! Take in a show!" Following the London subway bombings, the British were saying "just get on with it." Steve Ohr wondered aloud whether there wasn't something familiar
in this. He provoked these responses:
David Wald writes:
"Your 'life must go on' approach to terrorism does nothing to solve the problem. Just defying the terrorists results in a continuation of terrorism.
"Both engineers and doctors have a different approach. They seek to find the causes of the problem in order to find a remedy.
"The causes are no great mystery. The most infamous of the terrorists,
Osama bin Laden, has stated on numerous occasions, that terrorism is their response to certain policies and practices of the West, namely the occupation of Iraq, the US/European military bases in Asia, the corruption of Arab tyrannies (Saudi Arabia, etc.) and the support for Israel against the Palestinians. Nobody here wants to listen and insists, instead, on assigning the motive to 'hatred for our democracy and prosperity.'
"Well, if you won't listen to the horse's mouth you'll never find the answers. Even if some of what they say is BS. We need to listen a little and think about it. Ignoring it means repeating the same failed experiment."
And Jim Ford says
"Stephan: I enjoyed your recent editorial 'The only sane response to terror is to simply carry on" in the July 18, 2005 issue of EETimes.' I agree with you. We must take some precautions of course, but we do have to get on with our lives. Otherwise the terrorists have won.
"I also have seen the movie Brazil, although I don't have a clue why it was titled so. And I don't remember the scene you described, but there were a few other funny scenes that I do remember. In one, the Central Services workers come to the apartment of the girl, which is directly above the apartment of the poor guy who was suspected (wrongly) to be an anti-state dissident. That guy had been taken prisoner by the secret police when they drilled a hole in her floor (his ceiling) and slid down a pole into his apartment (that was pretty funny, and creepy, too). So the Central Services guys unwrap the paper off this big plug to plug the hole, but it's too small and falls through! Then one CS guy says, 'Damn, they switched to metric without telling us!'
"At another point in the movie, the protagonist (can't remember his name after 20 years) has the Central Services guys at his apartment fixing his climate control which has gone ape and turned his apartment into an arctic zone. The guys are in the space suits in the apartment working when Tuttle, I think his name was, the real dissident, also an HVAC engineer, arrives and swaps the CS guys' air lines with the sewer lines! Tuttle and the protagonist watch as the suits fill up with brown liquid and then explode!
"Well, I gotta go now. Brazil was brilliant, and I'm going to have to rent it again after all this time. Thanks for triggering the memories."
Those who remember Brazil recall that the "Tuttle" character was a walk-on by Robert Deniro...
Though we may not have an outlet for them, your recollections, comments, criticisms and other responses to anything you see here are always welcome. Use the "Feedback" path on the Planet Analog home page, or send your words directly to firstname.lastname@example.org. We look forward to hearing from you.