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  Infinity Hybrid Class AThe idea of a hybridThe PS Audio HCA-2 was the first power amplifier of its kind, utilizing two distinct disciplines in design to achieve its performance goals. Following closely on the heels of the HCA-2 comes the new GCA series of power amplifiers, integrated amplifiers and multi-channel amplifier. Combining the best of two technologies into one design, for the purpose of creating a warm, robust and musical sounding power amplifier, the GCA and HCA build philosophy was inspired by an earlier product with similar aspirations: the Infinity Hybrid Class A power amplifier. In honor of Infinity's inspirational thinking process that led us on our journey to build the HCA-2 and then the GCA series, we thought it important to tell the story of this fabled amplifier and its relationship to PS Audio. The Holy Grail The Holy Grail in high-end power amplification has been to try and marry the best sonic qualtities of all amplifier technologies together - including tubes, solid state  electronics and digital power amplification, while eliminating their weaknesses.Tubes are generally thought to excel in midrange, soundstage and midbass, while rather weak in bass and rolled off in the treble. Solid state designs are typically strong in the bass, dynamics and overall power delivery, while weak in the areas where tubes excel. Digital has long been thought to be sterile, bright and hard but amazing in its linearity, punch and slam. The used marketplace for power amplifiers is littered with past attempts at creating the best of both worlds encompassed in one design. Our lofty goal When we set out to design the new GCA series of power amplifiers, we wanted to make a statement and realize a lifelong goal of designing and building a revolutionary new product that literally swept all the attempts of the past under the carpet (including our own) and set the standards for pre and power amplification up to a new level. Raise the bar, so to speak. In order to reach our goal in the form of a power amplifier, it was obvious that we needed to get “outside of the box” with respect to our thinking processes. This could be no ordinary redesign, no polishing of existing technologies and topologies because almost every perturbation of what’s been done before has been tried in one form or another. This was a complex and challenging task, one that required us to separate the design into two distinct topologies: the input stage and the output stage. Clearly, these two entities of the design would have to be absolutely different from each other allowing us to take advantage of the “best of both worlds”. The PS Audio Hybrid Class A would be the first power amplifier product from PS that would  utilize this new thinking process: splitting the amplifier into two separate entities, each using a completely different topology for their particular task.The new GCA series would be the logical followup to the HCA-2 but would use the same notion: an independent analog input stage coupled with a revolutionary new SDAT™ output stage for the last half. In the GCA series, the analog input stage is also a revolution: it is called the Gain Cell™. It turns out this is not a new thought process It has been suggested that most new ideas are simply updated visions of what’s been done before. We as designers stand in the shadow of the great designers of the past. When audio designers in the early 1970’s began to realize that transistors were not the “be all, to end all” and that tubes had many sonic advantages to their presentation of music, the scramble was on to overcome these deficiencies and produce a solid state amplifier that would beat the tube. After all, tubes are hopelessly flawed as amplification devices: they are microphonic, fragile, have a limited lifetime and are (now) hard to get. Unfortunately, beating the tube sonically would prove to be a daunting task at best, one that has continued to elude designers for over 30 years. The first viable design One glorious attempt, which probably came as close as anyone had at the time, used a brute force approach. It was a hybrid. Instead of trying to replace the tubes entirely, it used them where they made the most sense, and got rid of them where they made the least sense. The brainchild of Arnie Nudell (a lifelong tube fanatic), then President of Infinity Systems , this rather brilliant plan would use the tubes for the input stage and solid state transistors for the output stage. Each section optimized for its particular job.  In 1978, Infinity Systems assigned audio designer, engineer and Audiophile Bascom H. King to design what would become the Infinity Hybrid Class A power amplifier. The Hybrid Class A amplifier was built using both technologies: tubes for the front end voltage amplifier, and transistors for the output current amplifier stage. After a year of work, that included help from engineer Bob Day who designed the physical package and the front panel interface, the amplifier was ready for production and, at the time, garnered rave reviews from J. Gordon Holt and others. Unfortunately, the amp was a bit ahead of its time, problematic, relatively expensive (back then, anyway), and after just a year of production was dropped from the Infinity line of products after selling only 100 pieces. Today, this rare breed of amplifier is coveted by its few remaining owners and fetches a healthy price tag on Ebay or Audiogon and other used equipment sites. In fact, this amplifier still sells for around half of its original retail price of $4,000. Not bad for a 25 year old design. PS Audio was lucky enough to purchase a pristine copy of the Infinity Hybrid Class A amplifier from the designer himself, Bascom King. The Hybrid Class A is a testament to the never ending quest for musical purity. If you are ever lucky enough to audition one of these gems, take it. They are a wonderfully musical piece of amplification magic and sound good even as compared to today’s modern amplifier efforts.  In honor of the Infinity Hybrid Class A So enamored were we of the brilliance of this “out of the box” thinking that when we completed the design of the first PS Audio hybrid amplifier, the HCA-2, we decided to use the same name as Infinity chose because the design thinking is nearly identical and, in fact, inspired by this early effort. Now, with the introduction of the Gain Cell, PS has again crossed the threshold of revolution. The Gain Cell is, in fact, the Holy Grail of amplification. Combined with the SDAT output stage, the Gain Cell and its output stage form the most advanced and unique hybrid power amplifier ever devised. The new line will be called the GCA series or Gain Cell Amplifier. Progress marches on, but it's important that we keep in mind the efforts of those great designers before us. For without their efforts, today's designers would have nothing to build their work on. It is with humble admiration we thank every designer that has come before us. |
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