A Tribute to Bob Sickler
Although the Audionics CC-2 is named after Cliff Moulton (Audionics' chief engineer) and Charles Wood (Prez of Audionics), as usual in the business world, the principals in the company masked the identity of the real creator - Bob Sickler, whose name appears as "RLS" on the schematics.
Since Bob passed away several years ago in Portland, the least I can do is give him the recognition he did not get at the time he designed the amplifier. This is the product that kept Audionics afloat in the late Seventies, selling more than 2000 copies in the US and overseas. There are still lots of people using them today, and I still get the occasional inquiry about repairing one. Well folks, you are on your own, unless you find an engineer or technician sharp enough to replace the obsolete Motorola transistors with similar types and is smart enough to re-compensate the feedback loop for the faster transistors.
Back to the story of the CC-2. In the mid-Seventies, Audionics wasn't doing too well. The amplifier designed by Cliff Moulton was extremely unreliable, with a field failure exceeding 50%. Some days we got back more blown-up amplifiers than we shipped out new. As anyone who's worked in electronics repair knows, it takes a lot longer to fix something than build it in the first place - most of the cost of electronics is the labor to assemble it. So Cliff's amp - the PZ-3 - was costing us a lot of money, and threatening the continuation of our jobs.
After six months CM finally figured out his amplifier didn't have enough phase margin, and the driver transistors were underspecified for Safe Operating Area (SOA) current. So if the speaker load was just a little squirrelly (and lots of dealers used speaker-switchers then), the amp would enter brief modes of oscillation, which would then exceed the SOA of the driver transistors, and the next thing you know, BANG! with a little wisp of smoke from the circuit board. Usually all of the driver, protection, and output transistors would be gone by the time we got it back.
The somewhat kludgey fix was to parallel three driver transistors (taking care of the SOA problem) and slow down the amplifier just a bit more. The PZ-3 was a pretty typical amplifier for the early Seventies - very high feedback, like a giant op-amp, very low slew rate (TIM distortion was then unknown), and questionable stability under dynamic loads. But the bench-test distortion figures into an 8-ohm resistive load were very low - in fact, the amplifier was named after its test figures, which was less than 0.03% distortion. (PZ-3, get it? Well, maybe it's funny to an engineer.)
Needless to say, even though the problem was fixed, the initial impression in the market was kind of wary - also, in all honesty, it didn't really sound that good, even though the distortion figure was lower than most other amps on the market. This state of affairs caused dissension in the company - Cliff thought that Charley and I were imagining things, while we thought that the PZ-3 didn't really sound that good, being kind on the harsh and gritty side (although at this time we were all accustomed to first-generation transistor sound). So the usual subjective/objective wrangle that has plagued audio in the following decades was right there in little Audionics on Sandy Boulevard in Portland.
When Audionics moved out to Beaverton (a suburb on the West Side of Portland), Cliff and Charley hired a new technician, Bob Sickler. Bob was not of the all-amps-sound-the-same school - he was excited by the theories of Matti Otala, who was exploring an entirely new form of distortion, Transient Intermodulation Distortion (TIM).
Matti had started a culture war within the US audio-engineering community, and we saw it right inside Audionics. The old-school engineers rejected the importance of this weird new form of distortion, and especially resisted the implicit criticism of negative feedback that Matti's theories implied. By the light of the conventional wisdom of the day (and some engineers still believe this), you can't have too much feedback. The only limit is the Nyquist Stability Criterion, which can be narrowly or widely defined, depending on how unpredictable you think the load will be.
Bob figured the way to answer the argument was to simply build a low-TIM, high-slew-rate amplifier and compare it to the PZ-3. Well, Hell Hath No Fury like a Chief Engineer Scorned, so Bob had to keep his little project to himself, or at least out of sight of his engineering manager. An appealing circuit appeared in a Fairchild transistor application book, and Bob re-designed it for the set of Motorola transistors we were already using in the PZ-3.
Although I was the speaker designer - and knew little of amp design at the time - Bob taught me what he was doing as he went along. After all, we tech types were in the back of the plant, while the big shots sat behind their wood desks in the fancy front office, trading stories back and forth and trying unsuccessfully to impress the secretaries. At least they left us alone most of the time, a blessing in the engineering trade.
Bob went beyond the Matti Otala AES Journal articles and investigated the relationship between speaker loads, phase margin, and slew rate. As the speaker guy, I could build some really ugly speaker-simulators, which Bob used to test his prototype. I knew from experience that speakers were extremely poorly behaved loads, not only reactive over many different frequencies, but also possessing high-Q mechanical resonances, and grossly nonlinear at high levels. As far from a 8-ohm resistive test load as could be imagined. As a result of Bob's insights into feedback stability and amplifier sonics, I added a four-element RCRC network to the Audionics tweeter crossover, making the speaker resistive all the way out to 500kHz and beyond.
Bob discovered - and I haven't seen this anywhere in the AES literature - that reactive loads ate up phase margin, which then in turn degraded settling time and slew rate. Put another way, an increased phase margin allowed a wider variety of speakers to be driven while knowing that the amplifier was still operating inside the design envelope.
Even though the evolving prototype retained the full complementary-symmetry topology of the Fairchild app note (this was quite a new circuit at the time), Bob spent most of his time not trying to dream up new circuit wrinkles, but making sure the amplifier was truly unconditionally stable into any load, with any input signal, while retaining its high (70V/uSec) slew rate. For test purposes, he removed the usual 70kHz low-pass filter on the input, and blasted the amplifier with ultrahigh slew-rate square waves from a Tektronix generator, while the amp was driving a custom reactive load at full power. This was a test that would instantly destroy just about every transistor amp on the market, whether it was high or low slew rate.
Bob was able to achieve 60 degrees of phase margin with the input filter removed, while driving a reactive load, and keeping the design goal of 70V/uSec or higher. As far as I know, this was unprecedented for 1977-78, considering the slow transistors we had to work with. To this day, there are plenty of transistor amplifiers that have a fit with reactive loads - in fact, home theater receivers are so poorly designed that some can't even drive a simple 4-ohm load, never mind the criteria set by Mr. Sickler in 1977.
Did Cliff appreciate this? Don't be silly. Not-Invented-Here had as much power then as now. Although Cliff thought the new amp was based on faulty engineering principles and just plain wrongheaded, at least he didn't try to fire Bob (that would happen three years later). Unlike Cliff, Charley very much liked the sonics of the new one, so Audionics put the new amp in production, naming it Cliff and Charley's Second amplifier (thus CC-2).
Cliff's contribution, if it can be called that, was to replace the long-tail resistors on the emitters of the input diff-pair with a weird little Zener-diode regulator, and to believe the vendor of the electrolytic caps when the vendor claimed the caps could be run right at the rated voltage with no effect on reliability (I'm not making this up). It took a year or so to finally kick the happy-cap salesman out the door and get a more reliable, higher-rated power-supply cap. Even so, the CC-2 was one of the most reliable amps ever made - if you excluded a handful of PS cap failures, the warranty-return rate was less than one in two thousand. By comparison, the usual figure for most electronics is between two and five per cent.
As the first US-made high-speed, low-TIM amplifier, the CC-2 collected rave reviews, which grew the market even more, and got Audionics into more than a hundred dealerships - the most in the company's history. Bob was going to design a new super-amplifier based on the new power MOSFETs (this was a year before the first MOSFET amplifiers appeared on the US market) when the plans were derailed by Charley signing an agreement with David Berning to produce an extraordinarily complex digitally-biased high-power (100W per channel) vacuum-tube amp.
Instead of the new CC-3 and new Bob-designed preamp coming out in 1978-79, Mr. Sickler spent a year and half designing and re-designing an all-TTL-logic (no microprocessor) logic board for the Berning amplifier. Audionics had never designed or built a vacuum-tube product before, much less anything with TTL digital circuitry, and David Berning lived in Washington DC, making for a lot of conference calls - this was not only before microprocessors, it was before fax machines, so a lot of schematics crossed in the mails.
The new-generation MOSFET power amp and preamp were never designed, the digitally-biased tube amp was extremely expensive to build and quickly failed in the marketplace, and Bob Sickler was fired from Audionics in a special ceremony in front of the assembled staff. Thank you, Cliff and Charley, for showing me how the high-end audio business really works. I had left for Tektronix six months before, so C&C never had the pleasure of humiliating me the way they did to the designer of their most successful, popular, and best-known product.
It was this experience that made me leave the high-end audio business for ten years. Never again would I ever work for anyone in high-end audio - the only way I would ever return would be as my own boss. Bob Sickler never worked in the high-end audio business again, going to work for a succession of low-pressure jobs in the medical-instrument sector. To this day, most people don't know that Bob was the first American to design a low-TIM, high-slew-rate, high-stability transistor amplifier.
His wife contacted me in the late Nineties, and she told me Bob was dying of skin cancer. We got acquainted again, and I gave him weekly Reiki treatments for three months, tweaking the custom-designed crossover of his tri-amped TAD-horn stereo system, and playing his favorite piece, the original film soundtrack to the "Shadowlands" movie about the life of C.S. Lewis. (Angel Records CDQ 55093.) Time would pass, we'd listen to the profoundly moving music on Bob's big hifi, his cats would make mischief and clatter around the house, and we'd talk about religion, God, hifi and the crazy things we did twenty years ago.
One day, Bob's wife called, and told me that Bob was no longer with us. At the funeral, I stood up and told the congregation about the time Bob had played a little trick on ol' Cliff, putting a five-cent Chinese firecracker underneath a PZ-3 that Cliff was trying to figure out. Cliff poked around and twiddled knobs, measuring here and there, trying to figure out why his amp just didn't work right, when BAM!
Cliff jumped back six feet, but got suspicious when the scope display was still working and there were rather un-electronic looking little bits of red paper underneath the amplifier. Bob couldn't hold it in anymore, started laughing, and Cliff chased him around the factory.
This is my memory of Bob Sickler - his sense of humor, and his insight. Thank you, Bob. You were a good teacher.
Power Supply Schematic
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