From: ruffrecords@yahoo.com
Ian Iveson wrote:
>> So my question is, how does the inductance vary with (dc)
>> current. If it measures higher with lower dc current then
>> if I use a 10W instead of a 5W but with a lower dc
>> current, do I get even higher inductance because of the
>> lower current?
>
> This isn't a simple question, IIRC from longago posts. I
> venture the following expecting a tongue-lashing.
>
> The inductance varies with the slope of the BH curve. If you
> look at one common, DC depiction of that curve, it appears
> as a sigmoid, shallow at the zero crossing because the
> magnetic domains exhibit what you might call stiction,
> becoming steeper, and then shallow again as the majority of
> domains reach their elastic limit, and some reach the yield
> point.
>
> The yielding dissipates power, resulting in hysteresis.
> Consequently, for AC, the sigmoid becomes a loop, steepest
> at the zero crossing, and shallow at both extremes of its
> variation. What's more, any AC signal will generate a
> sigmoid, with the magnetic bias affecting how flat or steep
> the sigma-shaped loop is, according to where its centre is
> on to the DC BH curve.
>
> Break for ridicule.
>
> Now, it seems from the DC curve that inductance should be
> zero as B crosses the H axis. Much nonsense arises from this
> interpretation. In fact, for pure AC the curve is steepest
> there, both on the upward and downward journey.
>
> However the sigmoid is flattish for small AC signals, so the
> mean inductance is lowish. Then it gets steeper as the
> signal increases, so the mean inductance rises, and then
> begins to flatten out at its extremes and the inductance
> falls again, as the core saturation approaches.
>
> Still with me?
>
> Add DC and small signals see a higher inductance, but the
> average inductance for larger signals doesn't increase very
> much, especially if the signal results in the core getting
> to the sharper curve approaching saturation.
>
> I would have thought that the great benefit of using a
> transformer rated for high DC current, assuming the same
> rated inductance, would be that it gives you greater
> separation between roll-off and saturation. That means you
> can use more feedback to extend its bass range at a given
> max signal. Alternatively, some designs bias the SE
> transformer and deliberately oversize it, to avoid the bass
> disappearing at small signal levels. So they say, I think.
>
> So, the answer is: yes and no.
>
> Ian
>
>
> "Ian Bell" wrote in message
> news:i8b07r$3jd$1@localhost.localdomain...
>> Just wanted to add a related question. In looking up SE
>> transformers on the net many that quote inductance do so
>> at a specified dc current. So the difference between a 5W
>> and a 10W transformer might typically be the 5W has a 10H
>> primary inductance measure at a dc current of 48mA whereas
>> a 10W type would have an inductance of 15H at a dc current
>> of 64mA.
>>
>
>> Cheers
>>
>> Ian
>>
>
>
Thanks for that. Not sure I understood it all. Magnetic theory I have always
found difficult.
From what I have read recently in RDH4 is seems that the more primary Henries
you have the better bass extension you get which makes sense sine the reatance
is in parallel with the load. Also the number of Henries you get depends on the
signal level being lowest at low signal levels and RDH4 recommends quoted
primary Henries should be measured at low levels. I have seem SET transformer
specs give values for primary inductance but not one mentions the level it is
measured at. I doubt it is safe to assume they are all made at low levels.
Cheers
Ian
--- SoupGate-Win32 v1.05
* Origin: you cannot sedate... all the things you hate (1:229/2)
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