标签: organ

It was an early autumn afternoon when I first saw her. It was my third year of engineering school, and what looked like the final year of her hell. She was propped up against some discarded trash, carelessly left in a mangled heap. Her innards were strewn about, hanging out a nasty opening in her back. I remember being dumbfounded that she was there at all... surely, someone would have noticed, called in about the mess. It seemed sick for someone to care so little about her... worse yet, I was practically salivating at this point... I had always wanted to play God. That night I gathered a trustworthy crew and an old Chevy, and we abducted her remains in the early hours of the morning. My crew helped me lug her carcass into the basement and promptly left me to my work. I grabbed my tools and carefully analysed her state of despair—tracing back her innards, determining if anything was missing. At one point in time, she was definitely a beautiful organ—a Hammond organ, or so the labels read. Now she was a hideous wreck, nothing but a scar on the face of our throwaway society. Some unskilled fool had clearly tried to service her back into health... her wires were everywhere (except where they should be, of course). Her cabinet speakers were dangling from their connecting wires. Sickening madness. Her 120V service cord had seen better days, her wiring mostly disconnected and hanging limp in her body cavity. I started my work by giving her a new power cord—ripping a replacement from a dead microwave. My beauty-to-be would be part organ and part microwave; this had me captivated. I carefully reconnected the entire wiring harness, remounted her speakers, double checked the connections, and as my heart pounded, I threw the switch. The lights came on. The hum of an open-input amplifier kicked in, gaining volume as the tubes warmed. My heart was racing as I reached down and touched middle-C, but not even a whisper. I meticulously fiddled with the tone controls, the volume pedal, anything I could to get a rise out of my monster. And yet, nothing. An empty shell of her former self. I switched her off, and returned to examining her carcass. Doubt started to set in. I checked the power connections for every sub-system: the power amplifier, the pre-amplifier, the DC power supply itself... nothing. They all seemed to work, throwing off heat and a warm orange glow from their dusty vacuum tubes. She was missing a voice—she just sat there, screaming nothing at the top of her lungs. Tracing the wires told me that the signals themselves came from a large nondescript metal box, the inside of which was absolutely packed with gears, actuators, and other mechanical-looking things. It was every bit as complex as the innards of an animal. All of this intricate metal—the bulk of my lady's weight—was ripe with grease and mechanical wear. She had certainly seen her share of players. I had her plugged in as I carefully looked over her corpse, and that's when I noticed that my girl was trying to speak to me... through all of her wreckage and despair, she had a little motor that was vibrating and throwing off heat, as it tried to start her mechanical being. To think that her little motorized heart had seized—the odds of me finding a compatible motor for my darling were slim to none. Doubt crept closer yet. While hopelessly trying to give the motor a manual start, a large metal can tucked in behind it caught my eye—could that be it? Her plagued little heart was an old AC motor, and all her suffering was at the hands of a dried-out start capacitor? I hurriedly tore a high-voltage capacitor out of that junked microwave, and crammed it in place of the old capacitor. I didn't even take the time to check values at this point—I quickly wired her up. I flicked the switch. The lights came on... my eyes widened. The hum of the amplifier began to rise over the sound of my own pounding heart. And the moment of truth I pushed my palm into her keys and out of her aching body roared the clamorous, atonal wreck of a mashed keyboard—I had done it! I had bent nature to my bidding, I had resurrected the dead... I don't know that I'd ever felt more accomplished. I excitedly poured over my new love, and we made haunting music well into the early hours of the morning. My townhouse neighbour would file many complaints. The lady and I would never care. Months had passed, perhaps a year, and my beloved and I had gotten well acquainted. We made music together in the darkness of my basement lair; I even dressed her up in modifications to hook into some guitar pedals. But, my precious was living on leased time. In fact, the lease to my building was coming to an end, and nobody in their right mind would help move my 300-pound lady up four flights of stairs to the new flat, myself included. She wasn't quite aware of it yet, but our parting was in the works. I put ads out to send her to a loving home, but nobody dared pull my beauty out of the basement I had her holed up in. The solution was clear in my mind. She had always been an entertainer—a final performance seemed appropriate. I sat and played her off into death, while friends and acquaintances destroyed her beautiful body with power tools and large, blunt objects... admittedly a savage death. We crushed my beloved into a heap of rubble, and I piled it into her dumpster grave that morning. Goodbye, my dear. You made for one hell of a party. Troy Denton is a computer engineering graduate from the University of Manitoba. When he's not working or sleeping, he's tinkering with embedded systems (and throwing the occasional workshop). He submitted this article as part of Frankenstein's Fix, a design contest hosted by EE Times (US).  

You may already know the Hammond B-3 organ—it was a fixture in rock bands in the 1960s and 1970s. You may not be as familiar with the Hammond A-100 , which is a console version of this classic organ . My mom has an early 1960s manufactured Hammond A-100 that was not working. She moved into a smaller house with no room for this spinet style organ, so we loaded it into the back of a truck (it's heavy!) and took it to our house. It sat untouched for almost three years, until I had a large chunk of time to take a look inside and diagnose the problem. This chunk of time came along in summer of 2004—the organ was about 40 years old at the time. We also had an old Wurlitzer organ I had repaired previously, and it was full of vacuum tubes, maybe 35 or 40, many for oscillators. When I opened the Hammond I was surprised to find only about a dozen tubes in an internal power amp and a big, long, heavy box suspended inside the organ enclosure. Simply as a matter of principle, I first replaced all the tubes in the amplifier and in the preamp of the built-in mechanical reverb. Afterward, the organ did in fact make tones, only not when the vibrato function was enabled. Before we get too deep into this story, some background on the Hammond "tone wheel" organs is needed. I've seen these organs described as "over-engineered," but my own description is "masterpiece." This machine is one of the most amazing electromechanical consumer products I've ever seen. The basic tones are generated by what's known as a tonewheel that starts with a synchronous electric motor whose rotational speed is set by the frequency of its AC power source, in this case, 60Hz. A shaft extends from the motor on one side, all the way across the width of the organ's internal cavity. A set of tone wheels are mounted on this shaft, which are not fully round, but instead, toothed wheels. As the shaft rotates, the teeth extend to almost touch a magnetic bar placed at the edge of the wheel. This whole motor and shaft assembly is mounted in that big, long, heavy, spring suspension shock isolated metal box. The magnets have a coil around their ends, and as a wheel's teeth pass by a magnet, they modulate the magnetic field, which in turn generates a current in the coil. The frequency of the AC current is set by the rotational speed of the wheel and the number of teeth on it. As an analogy, consider it as a guitar pickup that, instead of a vibrating steel string nearby, you have a rotating toothed wheel. The AC current of one or more of the 48 tone wheels is summed into an amplifier to make the organ sound, depending on which keys are pressed. Each key has a fundamental and eight harmonics. The standard signal path was working, it was the vibrato that was broken. I bought a copy of the service manual from Manual Manor and studied the schematic. There is also a service manual web page that discusses the operation of the vibrato. It describes a series of delays, via a cascade of low pass filters, that feeds into a rotating capacitive pickup. There is a cylindrical chamber driven from the same synchronous motor that drives the tone wheels, only on the other side of the shaft coupler. It connects taps from the delay line, in forward and reverse, to the amplifier's summing point by coupling them through a commutator inside the chamber via rotating air gap capacitors created by meshing parallel plates on a rotor with fixed plates in the chamber. After locating the signal path in and out of the assembly, an oscilloscope showed the signal out was shunted to ground when the vibrato was engaged. In other words, there are a set of static parallel plates through which a set of moving plates pass. The phase delayed signals are coupled into one of several sets of plates that create capacitors. The phase delayed signals are summed back into the primary tone to create a true frequency modulated vibrato (vs. tremolo which is amplitude modulation).   The chamber (upper left), the parallel plates, (lower left except two commutator plates centre right) and the phase delayed signal connectors (lower right). Also you can see the synchronous motor at centre left, which incidentally has a separate starter motor because the synchronous motor doesn't have enough torque to self-start. After a thorough examination of the disassembled contraption and more measurements, I figured out that 40 years of wicked (both wik-ed and wikd) oil had crystallized into a low impedance carbon coating inside the rotation chamber. Out it the garage, a long session with a spray can of Gumout and some rags eliminated the short circuit. Another four or five hours of careful reassembly, including re-stringing cotton thread through some tiny crevices, and IT'S ALIIIIIVVVVVE!! Brian Lowe submitted this article as part of Frankenstein's Fix, a design contest hosted by EE Times (US).  

Among young partiers in the 1970s, colour organs were a popular means of bringining psychedelic light shows (and possibly other psychedelic substances) into home rumpus rooms. These were generally made up of four strings of miniature Christmas lights, each string the same colour (red, green, blue, yellow) arranged in a pattern behind a screen and housed in a thin, square box. Four audio bandpass filters (bass, lower mid range, upper mid-range, and treble) controlled SCRs, which caused each light string to pulse to the amplitude and frequency rhythms of music from a stereo system. A typical colour organ can be seen here . The Heath company made a colour organ in the form of a build-it-yourself kit. One day a young guy came into the Heath retail store where I worked complaining that his colour organ was unstable. He said that he had to keep re-adjusting the sensitivity threshold of the light strings every time he moved the unit between his home and a friend's home. This guy, apparently, liked to party. Try as I might I could not reproduce the problem at my bench, once the trimpots were set so the lights just turned off with no input signal the settings stayed put. No intermittent parts or solder joints were causing the problem. I had to tell him that it looked like no fault with the unit and that it might be due to changes in the AC line voltage at the different locations, and that he would have to manually adjust the trimpots each time. At the time I had no means of varying the AC line voltage to test my theory. About six months later, Heath released a new isolated variac AC power supply product, and I acquired one for my bench. About this time, the same young man called up and said we really needed to figure out his problem—each time he had to pull the rear cover off the unit to mess with the trimpots and he was getting tired of it. (I suspected he was more likely having visual problems and was finding it difficult to get the screwdriver into the trimpot slots while seeing double.) But I told him to bring it in again, and since I now had the variac to test my varying line voltage hypothesis I was willing to give it another shot. Another nice effect of the variac was the isolation from the AC powerline that allowed me to connect scope probe grounds to the hot parts of the circuit. When I got the unit onto the bench I saw that my hypothesis about sensitivity to variations in AC powerline was indeed correct. When aligned at 110 VAC the light strings turned on when the voltage was increased to 120 VAC. When re-aligned at 120 VAC the lights turned on at 110 VAC. The exact details are a bit hazy in my mind; this was a few decades ago and a few of my own parties in between. But I recall that it had something to do with a charged filter capacitor at the output of the fullwave bridge rectifier, and that when the light strings were set to not turn on with no input signal, a residual charge remained that changed the SCR gate thresholds. When the line voltage changed, this charge caused the SCRs to trigger on every 2nd AC half cycle and light when they were not supposed to. The fix was simple—install a 10 watt resistor of a few kilohms across the bridge rectifier output to ensure the capacitor fully discharged each half cycle. Removing or reducing the capacitor caused another problem, but I can't recall what it was. Heath engineering approved the change and published it as a modification to be done when a customer complained about this specific problem. Glen Chenier, engineer, submitted this article as part of Frankenstein's Fix, a design contest hosted by EE Times (US).

It was in 1970 when I was 15 years old. I decided that I wanted a job working on electronics. I visited TV shops and such, and no one would hire me. My last stop was at Hoot Gibson's music store, where the owner (Hoot himself) made an interesting proposition: If I could fix a broken organ he had in his shop, he'd give me a job. The organ was acquired as a tradein, sight unseen. When Hoot picked it up, he realised that the owner must have attempted to fix the pedal section and left it disassembled and with all of the wires cut. The organ was a vacuum-tube Thomas, which was not a brand that Hoot carried. When I first saw the shape it was in, the likelihood that I could fix it didn't look good. But I really wanted the job, and it looked like a challenge, so I took him up on his proposition and began working on it. Besides, no one else had offered me the chance to do anything else. First off, I called Thomas and ordered replacement actuators for the pedals, because they seemed to have been the real problem. When the actuators came, they actually didn't fit. It appeared that along the way Thomas had changed the design. The new actuators were much better, so after drilling new holes in the pedals, I was able to mechanically reassemble the pedals, and it looked good. Next I had to reconnect all those cut wires. It didn't take too long to figure out how they likely were meant to be connected, so I hooked them up. I still didn't have a schematic, but I turned the organ on, and the pedals were working. That was the good news. The bad news was the organ had all kinds of other problems. By then I had spent a couple of Saturdays working on the organ and had made good progress. That was enough for Hoot, so he took me. Since the Thomas was going to be a long-term project, he assigned me some other units to work on. He also had enough confidence in me to pay for a schematic and a special contact cleaner that Thomas offered for $50. That cleaner was like brown goo, which seemed pretty strange, but it worked on the contacts. One of the problems I encountered on the Thomas was that its vibrato oscillator wasn't oscillating. I even replaced the tube, and it didn't help. Looking at the schematic, I noticed that the oscillator had no cathode resistor bypass capacitor, so I added one. That did the trick. Tuning the Thomas was painful. There was an oscillator per key—no top octave generators in those days and no dividers in this design. There was just an analogue oscillator per key and an inductor shared by three adjacent oscillators. These inductors could be adjusted as kind of a gross adjustment for the three oscillators. Then each oscillator could be adjusted separately. The thing is that adjusting one oscillator also affected the other two. Eventually, they would converge on a good tuning, but it took many iterations to tune every group of three oscillators. Note to self at the time: Don't forget to let the organ get to a stable operating temperature before tuning it. Hoot normally paid $7.00 for each organ repaired, regardless of the time spent. To my knowledge, he only ever paid more for this Thomas. He gave me $50 with the understanding that, after he sold that organ, I would make a house call if the new owner ever had a problem. I did get to make that house call, but only to clean contacts. I still had the magic cleaning goo, of course, so that was easy. Hoot, being the consummate salesman that he was, soon got the owner to upgrade to something better, and the Thomas was never heard from again. By the time I was 17, Hoot trusted me with the store's van, so I could make house calls. When there was a factory-mandated service update, the use of the van allowed me to do many of those updates. The factory paid me more for installing those simple updates than Hoot paid me for repairs, so I really liked that work. By taking the gamble that I could fix that hopeless organ, I got a job and a lot of experience. Hoot had nothing to lose, while I had everything to gain. I may not have been paid much, but I learned quite a lot. Shhh. Don't tell anyone, because it was probably against Illinois law for anyone under 18 to be doing that kind of work at the time. So maybe Hoot did have something to lose, but I didn't tell him. This article was submitted by Mark Rustad, Networking Division, Intel Corporation, as part of Frankenstein's Fix, a design contest hosted by EE Times (US).  

In 1970, when I was 15 years old, I decided that I wanted a job working on electronics. I visited TV shops and such, and no one would hire me. My last stop was at Hoot Gibson's music store, where the owner (Hoot himself) made an interesting proposition: If I could fix a broken organ he had in his shop, he'd give me a job. The organ was acquired as a tradein, sight unseen. When Hoot picked it up, he realised that the owner must have attempted to fix the pedal section and left it disassembled and with all of the wires cut. The organ was a vacuum-tube Thomas, which was not a brand that Hoot carried. When I first saw the shape it was in, the likelihood that I could fix it didn't look good. But I really wanted the job, and it looked like a challenge, so I took him up on his proposition and began working on it. Besides, no one else had offered me the chance to do anything else. First off, I called Thomas and ordered replacement actuators for the pedals, because they seemed to have been the real problem. When the actuators came, they actually didn't fit. It appeared that along the way Thomas had changed the design. The new actuators were much better, so after drilling new holes in the pedals, I was able to mechanically reassemble the pedals, and it looked good. Next I had to reconnect all those cut wires. It didn't take too long to figure out how they likely were meant to be connected, so I hooked them up. I still didn't have a schematic, but I turned the organ on, and the pedals were working. That was the good news. The bad news was the organ had all kinds of other problems. By then I had spent a couple of Saturdays working on the organ and had made good progress. That was enough for Hoot, so he took me. Since the Thomas was going to be a long-term project, he assigned me some other units to work on. He also had enough confidence in me to pay for a schematic and a special contact cleaner that Thomas offered for $50. That cleaner was like brown goo, which seemed pretty strange, but it worked on the contacts. One of the problems I encountered on the Thomas was that its vibrato oscillator wasn't oscillating. I even replaced the tube, and it didn't help. Looking at the schematic, I noticed that the oscillator had no cathode resistor bypass capacitor, so I added one. That did the trick. Tuning the Thomas was painful. There was an oscillator per key—no top octave generators in those days and no dividers in this design. There was just an analogue oscillator per key and an inductor shared by three adjacent oscillators. These inductors could be adjusted as kind of a gross adjustment for the three oscillators. Then each oscillator could be adjusted separately. The thing is that adjusting one oscillator also affected the other two. Eventually, they would converge on a good tuning, but it took many iterations to tune every group of three oscillators. Note to self at the time: Don't forget to let the organ get to a stable operating temperature before tuning it. Hoot normally paid $7.00 for each organ repaired, regardless of the time spent. To my knowledge, he only ever paid more for this Thomas. He gave me $50 with the understanding that, after he sold that organ, I would make a house call if the new owner ever had a problem. I did get to make that house call, but only to clean contacts. I still had the magic cleaning goo, of course, so that was easy. Hoot, being the consummate salesman that he was, soon got the owner to upgrade to something better, and the Thomas was never heard from again. By the time I was 17, Hoot trusted me with the store's van, so I could make house calls. When there was a factory-mandated service update, the use of the van allowed me to do many of those updates. The factory paid me more for installing those simple updates than Hoot paid me for repairs, so I really liked that work. By taking the gamble that I could fix that hopeless organ, I got a job and a lot of experience. Hoot had nothing to lose, while I had everything to gain. I may not have been paid much, but I learned quite a lot. Shhh. Don't tell anyone, because it was probably against Illinois law for anyone under 18 to be doing that kind of work at the time. So maybe Hoot did have something to lose, but I didn't tell him. This article was submitted by Mark Rustad, Networking Division, Intel Corporation, as part of Frankenstein's Fix, a design contest hosted by EE Times (US).