One month later than I thought it would take, the TCJ Push-Pull Calculator is finally here. The delay was entirely my fault, as I could not stop fleshing out the program. Originally, I planned on having not the multi-tabbed program you see on the previous page, just a single layer of a user interface, like a financial calculator, with only OTL output stage topologies supported. Then I added a graph and then more graphs and then three transformer-coupled output stage topologies and then the ability to save to and read from files… Ultimately, the program evolved into the sort of tool I like to use: easy to use and quick to find the right path, for art and science of designing amplifier is more like hunting elusive prey than simply looking up a recipe in a cookbook. The program also satisfies my requirement that I would be happy to buy the program for twice as much, if it were offer by someone else. At $19 USD until 1/31 ($24 thereafter), this program is a good deal indeed.

      What follows is a showcase for TCJ Push-Pull Calculator and ends with details on how to purchase the program.

 

TCJ Push-Pull Calculator Topologies

      TCJ Push-Pull Calculator covers eight different push-pull output stage topologies:

 

      1) Cathode-Follower Totem Pole Amplifier

      2) Grounded-Cathode Totem Pole Amplifier

      3) Mid-Referenced Totem Pole Amplifier

      4) Circlotron Amplifier (simple)

      5) Right-Grounded Circlotron Amplifier

      6) Grounded-Cathode Transformer-Coupled (fixed bias) Amplifier

      7) Grounded-Cathode Transformer (cathode bias) Amplifier

      8) Cathode-Follower Transformer-Coupled

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This is the output stage used in many new OTL amplifiers. While it offers no gain, it does provide a low output impedance and low distortion figure, the result of operating both top and bottom tubes in a 100% degeneration mode (cathode follower mode). The missing gain will need to made up in the input and driver stages. But as this topology more readily works without the benefit of a global-negative-feedback loop, extra gain isn't required to power that loop.

This is the output stage used in all of Julius Futterman's amplifiers and many other OTL amplifiers. While it does offer gain (relatively speaking, no tube will give any positive gain working into an 8-ohm load), it is burdened with both a higher output impedance and distortion figure, the result of operating both top and bottom tubes as grounded-cathode amplifiers. (The top tube's signal reference is the output itself, not ground.) Unless a truly high load impedance is driven, this topology requires a global negative feedback loop to lower its output impedance and distortion. 

This is the output stage explicated in the article Cars, Planes, and Circlotron. In spite of looking strange, this topology is the functional and sonic equivalent of the simple circlotron circuit used in high-end OTL amplifiers. The power supply is not grounded, but left floating instead. Why bother making a confusing looking amplifier? This topology, like the circlotron, offers the advantage of not needing any signal level compensation for its top and bottom tubes; in other words, both top and bottom tubes are fed the same signal amplitude (but differing in phase, of course). Unlike the circlotron, this topology can use a single center-tapped power transformer, rather than two separate transformers. Its output impedance and distortion approaches the cathode follower totem pole.

This is topology is called "circlotron,"  as it is seen as being subtractively derivative of the old Wiggin's circlotron circuit. It forms the backbone of  several high-end OTL amplifiers. Two  power supplies are needed per channel. This topology, like the mid-referenced totem pole, offers the advantage of not needing any signal level compensation for its left and right tubes, as both left and right tubes are fed the signals of the same amplitude, but 180 out of phase with each other. Its output impedance and distortion falls between the cathode follower and grounded-cathode totem pole topologies.