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I read most of your posts, and find you to be very knowledgeable ...

Posted by KIS (A) on January 24, 2007 at 18:39:51

In Reply to: IMHO posted by Russ57 on January 24, 2007 at 15:53:43:

G'day Russ

So I would like you to consider my point of view below and tell me if I am off course:

When the impedance of the OPT increases, the tube sees an easier load making tube amplification distortion lower. But this is in the expense of power, which may not be a big issue.

However, my concern is more with the OPT ability in performing at lower impedance. ie how the OPT will behave when a speaker impedance is 2 Ohms or worse 1 Ohms. Speakers such as Quad ELS57s.

My transformer expert tells me that when I specify a higher impedance OPT, it would mean that the performance of that OPT will not be as good with lower impedance speakers ie 4 Ohm tap is not going to be good. It has to do with the number of turns. The bigger the difference in impedance (6k step down to 4 Ohms compared to 3.5k down to 4 Ohms) between OPT impedance and output taps, the worst the performance of the OPT - especially in the high frequencies. Internal capacitance will always be higher if the same configuration is adopted (relatively speaking). So most high impedance OPT would need more feedback to get high frequency performance.

And I do not like GNF in SET or PP ( I have heard and tried many SET and PP, and I suspect some just listens for bandwidth and good bass, rather than the purity of tone and harmonics) despite what I have seen written here by some of the most respected posters.

So the question is whether we favour the tube by giving it easier load, or we favour the OPT?

I come to the conclusion that OPT needs to be given as much help as possible, as it is technically the most difficult component to get right. Also the extra power would be helpful in lowering distortion as well.

Is my thinking sound?

Cheers
Will

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