Cookie Jar

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engineer

Specialize in designing sensors and data acquisition systems that work in severe environments with minimal power.


Cookie Jar

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  • 09.17.2012
  • Help an engineer with Heathkit repair
  • I first got into electronics via Heathkit in 1957 and built a myriad of of their kits including their PCs into the 80's. When Heathkit had their closing sale at their local outlet, the atmosphere was that of a funeral parlor, and nobody seemed in the mood to buy the bargains. I still mourn the loss of Heathkit. The piece of equipment I put the most hours on is my prized 1969 vintage Quad (Acoustical Corporation) stereo system, with electrostatic loudspeakers, Quad 33 pre-amp and 303 power amp. These Quad components have outlasted generations of tuners, tape recorders and even a handful of CD and DVD players. On the couple of occasions when I had noise problems, I traced them down to capacitors. With new parts on hand, I was surprised to observe that it was actually the solder joints at the capacitors that seemed to have crystallized. One was on a PC board the other on a power supply capacitor's terminal. Sucking off the old solder and doing a nice clean solder joint fixed the problem. A good rule of thumb is that in modern electronics 95% of your faults are due to bad connections. Always force yourself to start there when doing a repair.
  • 09.17.2012
  • Help an engineer with Heathkit repair
  • I first got into electronics via Heathkit in 1957 building their myriad kits right up to their PCs in the 80's. I don't know if it's just my luck, but they all still work well.
  • 09.17.2012
  • Help an engineer with Heathkit repair
  • I first got into electronics via Heathkit in 1957 building their myriad kits right up to their PCs in the 80's. I don't know if it's just my luck, but they all still work well.
  • 08.29.2012
  • Consumer audio: Is accurate sound overrated?
  • All the literature I've read recently about room acoustics simply ignores the overriding effect of the fundamental room dimensions: length, width and height. The usual thing that's mentioned about dimensions is that the longest dimension determines the lowest frequency that can be effectively reproduced. We know that each dimension will resonate frequencies and their multiples related to the half wavelength of that dimension. How can we make sure that the resonant frequencies of all three dimensions are evenly distributed up the octaves? The magic ratio is the cube root of two 1.25992! KISS In our house we built two rooms that follow the formula. One is our living room, full of the usual sound absorbing furniture, curtains etc. The other is a sun room with hard glass on three sides and a hardwood floor. Recordings I've made in both rooms sound great. In fact the live sun room with it's long reverb sounds fantastic - like some large concert hall. Some of the best sounding concert halls in the world are rectangular boxes with varying reverb times. I'm willing to bet that their fundamental dimensions follow the ratio of the cube root of two. In my opinion the main purpose of the complex and expensive sound absorbers and reflectors is to damp down resonances caused by off the cuff room dimensions. Remember KISS.
  • 08.29.2012
  • Consumer audio: Is accurate sound overrated?
  • There's a renascence in vinyl recordings these days because many people say they sound so much better than CDs. What is it that is better - more noise, clicks, rumble, more distortion and poorer frequency response from this technically decrepit mechanical system? Most studio recordings, because of their wild and piercing "equalization" settings have to tame things back down when cutting a disk so the stylus doesn't get launched out of the overlapping grooves. So yes, vinyl does sound more mellow, not because of the vinyl but because of the half deaf sound engineers "equalization". A good demonstration of how bad the studios are is the sound of a "boom car". It goes BOOM tch tch BOOM tch tch. The tch tch is the energy in the 2Kz to 6Khz to give the recording punch and presence. I find in my home system I often have to turn off my sub-woofer because I don't appreciate chest compressions when listening to some sound sources. So yes, the observant customer is always right even if she doesn't know the first thing about technology. It also goes to prove that most technologies can be turned into assault weapons.
  • 08.29.2012
  • Consumer audio: Is accurate sound overrated?
  • I once attended a course on studio recording at a well known recording studio. I was appalled as to what was taught about "equalizing" the sound. The teacher tweaked every knob on each parametric equalizer for each sound channel for maximum "punch" to what I would call piercing. Monitoring was done at deafening sound levels. We were informed that this was standard studio recording practice. This "equalizing" process was then repeated when it came time to make the master CD by another expert in this field. It would appear that to earn his keep, a recording engineer is expected to adjust every single knob on his mixing board. It's small wonder that so many recordings sound terrible when played on good audio equipment. How can one possibly judge the sound of an audio system when the the frequency and phase response of most sound sources has been so messed up?
  • 08.29.2012
  • Consumer audio: Is accurate sound overrated?
  • Speaker and especially headphone transducers deteriorate rapidly with age due to temperature and humidity effects as well as fatigue. This deterioration doesn't have a direct relationship to original specifications or cost. This is why a transducer that ages gracefully can sound much better to the ears than one that doesn't.
  • 08.29.2012
  • Consumer audio: Is accurate sound overrated?
  • Most published speaker measurements lie like a rug. A speaker enclosure has 3 fundamental dimensions which will result in resonances in multiples of the half wavelength and multiples right up the audio spectrum. The Q of these resonances will typically range from 10 to 20. If one dimension is the same or a multiple of the other, the resonances are boosted. To evenly spread the peaks up the audio spectrum the fundamental dimensions of the enclosure should relate as the cube root of two. To avoid revealing these nasty resonant peaks, speakers are typically tested with pink noise so the high Q resonances have no chance to build. Unfortunately music consists of frequencies held for significant time and the resonances will obviously color the music to the ear. Every manufacturer wants his specs to look good. Testing realistically would significantly worsen the numbers. So most speaker and amplifier specifications are meaningless to real world performance. So if ear tests don't correspond to instrument tests, you're not testing honestly.
  • 08.29.2012
  • Consumer audio: Is accurate sound overrated?
  • Being involved in instrumentation design, I was always a bit skeptical that a certain amplifier or speaker could sound better or worse than than measured results. One day on a whim, I hooked up my distortion meters to the actual speaker terminals of my living room stereo, and I was in for a rude awakening. The distortion readings were a couple of orders higher than for a pure resistor load! Not only that, but the frequency response drooped quite significantly above about 6Khz using lamp cord. When I tested various other power amplifiers, I found that their performance under a speaker load bore no resemblance to their performance under a resistor load. Performance also varied wildly with the particular speaker systems used. A full range electrostatic by Quad made many amplifiers go unstable and most perform very badly. Not surprisingly, the Quad amplifier seemed unaffected by actual speaker loads. Speaker cables did have a significant effect on frequency response and distortion. So if ear tests don't correspond with instrument tests, you're not testing properly.
  • 08.02.2007
  • Applying solenoids: Flying blind is not recommended
  • I have two suggestions for the article on applying solenoids. 1. Eliminate the high side MOSFET. I can't see the purpose it serves, except to add a symmetrical appearance to the to the schematic. By eliminating it you save its cost, its resistive and switching losses, and the need for a bootstrap driver. You'll need some more 0 ohm jumpers though. 2. Put your inductive kickback diode directly across the solenoid valve coil, preferably right at the solenoid. This would greatly reduce the current loop for the inductive kickback current. The design shown, with two diodes, allows the kickback currents to circulate in a lot of conductors and feed directly into your main battery power supply rail. I would expect noise problems worsening as the battery impedance rises with age. A straight diode may lengthen the solenoid's magnetic field collapse time. I would suggest selecting a TransZorb of suitable voltage to give a decay time independent of your power rail voltage and impedance.