Berning ZH-270 Replacement

Chris74, I humbly suggest that you have no idea what you are talking about. The output transformer in the Berning is clearly visible in the patent schematic! -even if you take the tack that an air core transformer is not in fact a transformer (which of course it is), ignoring the role that the semiconductors play in the output section still puts it outside the category defined by the acronym 'OTL'.

It is true that in the early 70s and late 60s, Allied Radio Shack referred to some of their amps as 'OTL', but generally the term refers to a tube amplifier, not semiconductor, and also not an amplifier that uses both a transformer and semiconductors for impedance transformation in its output section.

Of course, cats are distantly related to dogs, so I guess all dogs are really cats, right :)

BTW, the Atma-Sphere approach to OTLs was patented in 1986, and is not a Futterman circuit or a derivative thereof. Contrary to your assertion, it is *unconditionally* stable, as the amp cannot be made to oscillate under any load condition, regardless of input signal condition. It was the development of a fully symmetrical circuit that is inherently low in distortion that allows for this, so feedback (a destabilizing feature in any amplifier design) was no longer required, unlike the prior art.

Bpinder, just a FWIW, This topic comes up again and again, and every time I wind up with a bunch of messages about the thread in my email box. I try not to respond unless there is just plain and simply misleading or outright false 'information'. That will cause a response, simply to set things straight.

In this case, my company was mentioned specifically in conjunction with false statements about our products.

Hi Chris, if it were as simple as that!

The Futterman is a 'totem-pole' circuit and is asymmetrical. Our amps use a modified Circlotron which is half the output impedance and *is* symmetrical. Futterman amplifiers usually have output coupling caps and large amounts of feedback, our amps employ neither. Pretty big differences- they amount to reliability and performance, part of why I've been able to be at this for over 31 years, longer than Futterman at this point.

You can look all this stuff up on the web; mistaking our amps for Futtermans has been one of our biggest marketing problems. This is what I meant when I commented that you did not know what you were talking about- it was not meant in a mean way, just simply that that it is the case.

We have a direct-coupled output and so does the Berning, but the Berning uses a DC to DC converter *and* an air-core output transformer for the power tube(s). Neither the latter nor former will be found in an OTL, in which impedance conversion is done by the tubes and the tubes alone.

I have been very careful to underline my admiration of the ingenuity of Berning's concept in the past and that has not changed. I think its brilliant! -but an OTL it simply is not.