Of course, in the ego driven audio world, they often do believe they have invented the next perpetual motion machine (many of which, btw, are also patented).

  Thank you for pointing this out to me. I can see how a preemptive strike is needed to prevent other companies from patenting what they copied from your own efforts. Still, I find it sad that a silly patent can exist at all. 

Subject: ...and measurement claims -- you're correct
…about the max power output for class A SE amps. This error I made myself in scope measurements on transients.  One-sided peaks can go much higher than peak-peak since the amp is heavily 2nd order distorted and when AC coupled the high peaks can shift up much higher than the opposite low end as the low end stays on for extended period of time - clipping into class C operation actually. So I can see where the 60W peak power measurement from a 2A3 might be mistaken. Integrated over the conduction period it can get pretty high, but over the full cycle with cutoff period included, no chance.
   In the world of tube amps, there is a definite lack of solid claims made. But it's so esoteric anyway that people into the high end of this probably should already realize it and find out how it operates for themselves.  If I knew the Atma-Spheres had an output impedance of 13 ohms I think I never would have bought their kit, but I think I'd have missed out on a great amp.
   And I agree about the patents in logical terms, but I'm no patent attorney. Some trademarks have been allowed that stunned me.  Like being able to trademark the 900 series of numbers for Porsche models, or a decimal point for a model
number in a case between Bose and Thiel, the 2.2 vs 2 2 or whatever?  Absurd to me.

Subject: Tube driver for electret headphones
   The November issue of the Tube Cad Journal discussed the building of a driver for electrostatic headphones. I have myself two relatively cheap electret-type electrostatic headphones from Stax. The quality of these transducers is relatively good, but the transformers which were supplied with them seem to be a limiting factor. Therefore I would like to build a transformer-less electret headphone driver. I suppose that the drivers in the November issue of your journal cannot be used with my electrets, is this correct? And if this is true, would you be willing to discuss electret driver topologies in a future issue of your webzine?

  The two types of headphones are functionally identical save for the need for a biasing voltage for electrostatic headphones. The electret-type come pre-biased.
  While the sound from electret-type headphones can be very good, the relative efficiency is usually less than that of the electrostatic headphones. Consequently, plan on needing more voltage swing for these type of headphones.

Subject: Class A patents
  I wanted to make one comment on patents.  I work in the electronics field in power, and as in audio amplifiers, the same ideas are patented over and over. One reason you may have overlooked is very important to the companies: they need to protect their own right to manufacture their product. When the next company comes along with a silly patent, they can hold theirs up, and claim that they invented it first. In many cases, there is no choice but to do this.

pg. 15


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