Ergh, a few things...

I don't know why the java page has both load impedance and output impedance.

"amplifier load impedance" should be "effective speaker load"

"headphone input impedance" should be "effective headphone output impedance"

"amplifier attenuation" would make more sense inverted and expressed as a fraction (at least to me it does)

it would also be nice to express it as a change in dB (equation is 20logA where A is the voltage divider ratio)

I haven't chequed the actual calculations/equations yet. There seem to be a lot of nested logic statements in there though... but if the equations are set up correctly, you should be able to input values of zero and get valid answers

Scenario 0: no resistors at all

- if you don't have a problem with noise and you have enough useful range on the volume pot, then don't mess with a good thing

Scenario 1: load resistor

- a safety precaution for transformer coupled tube amps

- also may be used for amps that are designed for specific stable speaker loads

- does not affect output to the headphones at all (in theory) when used by itself

- use this scenario if you already have good control of the pot with no noise, but you're paranoid about damaging your amp because you don't know what kind of load it needs, if any

Scenario 1.2: you should add another scenario here which is only a series resistor

- this is a voltage divider with the ratio formed by R2 and the headphone, which means dynamic headphones with changing impedance curves will experience changes to frequency response

- use this scenario if you need more range on the pot and/or want to reduce noise, and you have a planar magnetic headphone

- may also be used with a dynamic headphone, but frequency response may not be accurate (some may prefer this in fact)

scenario 2: dual resistor A

- basic voltage divider configuration; ratio controlled primarily by the resistors (and affected only slightly by the headphone)

- use this scenario if you need more range on the pot and/or want to reduce noise, and you have a dynamic headphone and what more accurate response

scenario 3: dual resistor B

- the configuration used by the Hifiman adapter box

- essentially scenario 1 and 1.2 together, so a voltage divider plus load resistor for stability

- use this scenario because you like your women like you like your coffee... covered in bees

scenario 4: three resistor network

- basically scenario 2 plus scenario 1 to give the amp a more stable load if you're using a dynamic headphone with large impedance curves

- only use this scenario if you need to reduce noise and gain, AND you have a headphone with wild impedance curves, AND you're paranoid about your amp's loading requirements

Edited by Armaegis - 12/2/13 at 11:58pm