Balanced Speaker Outs for SII

[Paul Birkeland]

Perhaps you should try a pair of 1K resistors and see what happens.

[Deke609]

I was afraid you might say that 

[Tom-s]

And? How did this experiment turn out?

[Deke609]

To my surprise, I noticed no difference between 80 Ohm and 1K Ohm resistors. I was expecting a big jump in volume. I didn't measure voltage at the speaker taps -- just used my ears.

I'm clearly not understanding something basic here.

[Paul Birkeland]

I was expecting a big jump in volume.

When you have a reasonably low output impedance, the level will not change much provided the loading impedance is much greater than the output impedance.  If you want to do this experiment and hear a dramatic difference, try 80 ohm resistors and then 1 ohm resistors.  (I don't recommend leaving the 1 ohm resistors though!)

[Deke609]

When you have a reasonably low output impedance, the level will not change much provided the loading impedance is much greater than the output impedance.

This is what confuses me. With the 80 Ohm resistors, the output impedance of my headphones (200 Ohms) was slightly greater than the load impedance (160 Ohms). So when I switched to 1K Ohm resistors (I think they are actually 1.2K), I figured I'd get a big jump in volume b/c now the load is more than 5X the output impedance.  I assume there was in fact an increase in volume ( I was lazy and didn't do a A/B comparison) but it wasn't nearly as big as I thought it would be. I don't know whether the fact that I tend to listen pretty loud affects things.  I was expecting a jump in the order of a full click on the coarse attenuator or more.

[Deke609]

Maybe I should try 2K Ohm resistors?

[Paul Birkeland]

This is what confuses me. With the 80 Ohm resistors, the output impedance of my headphones (200 Ohms)

Headphones are the load impedance.  Output impedance is a characteristic of an amplifier.  The output impedance of the Stereomour on the 8 ohm tap is going to be around 2-3 ohms.

-PB

[Deke609]

Aha! Right!  Still don't understand why this is, but now I have a direction for reading up. Many thanks PB.