[Ian Bell[_2_]]

flipper wrote:
On Sat, 02 Oct 2010 11:03:10 +0100, Ian
wrote:

Ian Iveson wrote:
One thing I was wondering was if I use a transformer
with
a nominal 16 ohm secondary but use it with 32 ohm
headphones for example, then ra reflected into the
secondary would be so low relative to the load that the
output could be considered essentially a voltage source.
Equally the load reflected to the plate would be four
times higher so distortion would be lower?


Language. Lower load = higher resistance.

If you follow my logic, my point is clear. The load
presented by the primary of a transformer comprises:

1. Primary winding resistance
2. Leakage inductance in series with 1
3. Reflected secondary winding resistance in series with 1
and 2
4. Reflected secondary load in series with 1, 2 and 3
5. Primary inductance in shunt with 3 and 4

Think.


Nope, maybe I am just thick. You said "10H is in shunt with load. Lower load makes shunt more
significant."

Now you are saying "Language. Lower load = higher resistance."

Which means "Higher resistance makes shunt more significant"

That means to drive a higher resistance load I need MORE inductance in the primary.

Does not make sense to me.

It's because the inductance is in parallel with the load impedance.

With a 5k (or any other value) OPT you'd like it to be that same
impedance at all frequencies but it won't because the inductance
impedance, which is in parallel with the load impedance, falls in
value as the frequency decreases, so the parallel value also falls.

Let's pick a convenient reference point: effective impedance half of
nominal. That's going to occur at a frequency where the 10 Henry
impedance equals the OPT nominal impedance, I.E. 5k. If the nominal
OPT impedance is 10k then that (parallel impedance half of nominal) is
going to happen at a higher frequency.

Now, that was presuming the EL84 in pentode mode where the tube's
anode impedance is high and, so, not much of a factor. See Patrick's
post for triode mode.


Yes, you are of course right. I have a stinking headache today and I just cannot think straight.
Bigger L means higher Zl or lower load - duh??

Cheers

ian

Cheers

Ian

Ian