HD83, how to use low and high impedance cans?

[A Stuart]

You would lose the best part of 20 decibels of signal level with this resistor. Also the headhones would see a very high impedance source so volume might vary strongly according to the headphone impedance at different frequencies.

I was just trying to work out if you could use a switch. I can't see that you could arrange it without the signal passing through about 6 switch contacts per channel.

A compromise could be to hardwire the windings in series (ie leave them unchanged ) but either via a switch or a second socket, feed the low impedance phones from a single set of the windings.
Admittedly the headphone would see 4x the resistance in the windings but I think, correct me if I am wrong, it would not upset the impedance seen by the amplifier. I dont know about inter-winding capacitances etc etc, but on a basic level, magnetically, the primary does not know if the secondary is drawing eg 1mA x 100 turns in one wire or 4 x (0.25mA x 100 turns) in parallel. It would be just like a thicker-wired version of the same 100 turns.
I don't believe you should lose signal level other than that attributable to the resistance of the non-paralled winding.

Again correct me if I'm wrong but I can't imagine headhone currents overheating a transformer winding.

Alastair.

PS if you used a switch, take care to arrange it so as not to short out the other three windings!