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Most exotic 3.5kOhms Output Transformers
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Old 1st December 2012, 04:04 PM   #31
dave slagle is offline dave slagle  United States
diyAudio Member
Join Date: Mar 2003
Location: NYC
Originally Posted by petavgeris View Post
I have a graph somewhere.
With a gap and DC bias there is an initial substantial increase in mu, then mu is almost dead flat and then it starts to go down due to saturation.
I would like to see that graph.

That's one of the main virtues of SET amps. Push Pull gives terrible sound compared to Single Ended because there is no DC bias and initial effective permeability of iron is quite low, so low level detail gets lost.
or it could just be the airgap required for DC linearizes the inductance.

It is this low level detail where magic of music lies! This has nothing to do with the amplitude of the signal, it is purely a function of DC bias. Gap and DC is all the magic of SET amps!
I agree with the concept that music lies in the low level details but have yet to witness DC current increase the perm. As an experiment I measured a choke I had on hand. 49% nickel core with 0 DC current I measured 144hy's with a 0.5V 50hz signal applied. (this represents an AC flux of 3.5 gauss) Applying 1ma of DC current (Bdc of 236 gauss) did not alter the inductance at all. Granted this device had a substantial airgap which could hide a slight change of perm so I placed a minimal gap (0.0005") and remeasured.

This time I measured 810hy's and interestingly enough 1ma of DC did bump the inductance a bit. This was simply the DC current pulling the core together which has the effect of shrinking the gap. A few large clamps secured everything in place and the inductance now measured 950hy's. I then applied DC in .1ma increments and it wans't until 1.8ma that a change was noticed and that was the slight reduction of Q that predicts the onset of saturation. 2.5ma of current dropped the inductance to 890hy.

Finally I changed the excitation frequency to 120hz to reduce the net flux to 1.4 gauss and the inductance dropped to 900hy but I was unable to get an increase in inductance by applying DC. To close up this experiment I did the calculations based on the selected airgap and a 25% increase in perm translates to a 1.5% increase in inductance which should be observable if it existed.

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Old 12th February 2016, 10:45 AM   #32
jbercovici is offline jbercovici  France
diyAudio Member
Join Date: May 2009
this is a long time after...
What was the winding technique meaning how many P and S layers ? What was the insulation material between P and S layers ?
Did you experiment Finemet Nanocrystal cores ?

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