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In Reply to: Re: Berning ZH270 or Seigfried compared to Atma-sphere MA60 posted by allanbhaganinfo on June 14, 2005 at 20:11:05:
The tubes see the speaker characteristics and vise versa, no transformer made can allow that to happen if it's in the signal path!Unfortunately, perhaps, his patent application for this idea describes it as having as an essential component, a transformer smack dab in the middle of the signal path between the output stage and the load (e.g. speaker).
No, not at all, this is not a accurate statement!
Yes it is a reasonably accurate statement, because another essential component of his idea, as described in the same patent (#5,612,646) are groups of power mosfets (also in the signal path), which are known in switching power supply and Class D amplifier circles as comprising an 'H Bridge' configuration. These power mosfets are switched between 'saturation' mode and cutoff, also typical of their application in switching power supplies and Class D amplifiers.
Follow Ups:
H Bridge is a building block for power conversion technology, so a accurate statement would be such and nothing more than the ZOTL uses modern power conversion technology to achieve it's goal, but I can't see a accurate resemblance at all to a high efficiency digital pulse width modulation Class D amp, if so, then the ZOTL equally have some resemblance to all laptops, computers, some modern TV's most all avionics and so on and so on, it's just not accurate.Maybe I miss understood your first postings, you hinted it resembling a transformer coupled amp, then it was some resemblance to a Class D amp, which would suggest a hybrid, which made my answer just as confusing, I should have said no hybrid made can allow that to happen (referring to tube/speaker characteristics), not no transformer.
OTL means output transformer less, one would assume that it means audio output transformer less, what else could it mean, which is what the ZOTL is, the key is that the device is not in the audio frequencies, which is what I mean when I say not in the "signal path" I mean audio frequencies, what other signals is there, yes there is a RF matching device in the circuitry operating at 250Kh which is made up of several transformers and mosfets, the point is, it does not operate in the audio frequency.
The amp is output transformer less and match varying speaker impedances, with a capable frequency response of DC to 250Kh, show me another tube amp that can do that, clearing showing it's an advancement in design topology.As I posted elsewhere, read Charles Hansen report, he is a switching power supply engineer, where he clearly states that this amp does not operate like a Class D amp, here is the link again.
http://www.davidberning.com/hansen_on_zh270.htm
I don't mean to cast aspersions on David Berning's ingenious circuit or to deny his basic claims for its capabilities, which in my estimation, include removing the typical tube amplifier output transformer nonlinearities while adding the capability to respond down to DC and retaining the ability to transform the voltage/impedance between 'primary' and 'secondary'.It's just that the means by which this is accomplished will presumably add its own sonic characteristics, and that the tendency is, since it is encouraged to generically refer to it as an 'OTL', to casually assume that no transformer at all exists in the signal path between output stage and load. But you have made reference to this already.
Btw, I've designed a 'conventional' OTL that indeed does repond down to DC (as in amplifying a DC voltage presented at its input - I deliberately rolled it off to unity gain at DC to minimize voice coil mayhem, however) with output offset referenced to ground in the tens of millivolts or less without any solid state devices in the signal path whatsoever and without resorting to the use of a feedback servo, and with some tweaks to the input and driver stages, could also respond flat to 200khz (as is, my prototype measured 3db down somewhere past 100khz into 8 ohm).
"It's just that the means by which this is accomplished will presumably add its own sonic characteristics"I would love to hear what a "sonic" characteristic of something operating at a fixed frequency of 250Kh would be?
But for argument sake let's say Maybe, so a conventional OTL with a power supply of 60Hz (audio Frequency) would not have a sonic characteristic?
One would think moving everything out of the audio frequencies would have less of a sonic character than one in the audio frequency like a 60hz one, using your own logic or any!
If low impedance, varying speaker loads where not a problem then there would be no need for transformers, you need to have the same current transfer characteristics into 2 ohms as you do into 12ohms.
If you have a speaker with a 10R impedance characteristics as flat as a ruler from 20hz to 50Kh, conventional OTL's will be the only way to go but very few speakers do that if any, this design has opened the OTL's character to varying speaker owners not just OTL friendly ones.""I've designed a 'conventional' OTL "" etc etc!!
Yeah, that's not a problem but does it match varying speaker impedances, do that and have a DC to 250Kh response and you'll have our interest, that's for sure :)
Anyway, I've spent much too much time here trying to explain something that again is very complicated indeed and we've gone over an over it in the past, this amp DOES exactly what a OTL can and what a transformer coupled amp can and it's not a solid state hybrid, so what is it, it is what it is, nothing like it.
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