Bam!

[Doc B.]

This is a thread about the Quicksand, not the Quickie, so I'm little unsure of the question. No, the Quickie is not suitable for 40 ohm headphones, it's a preamp. Yes, the Quicksand would work quite well.

[m17xr2b]

Yes I meant the Quicksand. Now for the big questions, what is the output impedance of the headphone output? And if I would like to limit the power of the headphone jack so it will not be too loud using headphones with high sensitivity could this be done by changing the resistor on the headphone jack?

[Paul Birkeland]

Yes I meant the Quicksand. Now for the big questions, what is the output impedance of the headphone output?

There are two options while building presented in the manual, you'd want to use the high impedance resistors.

And if I would like to limit the power of the headphone jack so it will not be too loud using headphones with high sensitivity could this be done by changing the resistor on the headphone jack?

Yes, this can be done.  If you want to strongly limit the power, you may end up wanting a set of 4 resistors to both lower the output and keep the output impedance more reasonable.

[badman]

Since we're talking about resistors and phones- has anyone measured the frequency response with the output resistors in place (instead of the jumpers)?  Class D amps, like this one, have a 2nd order filter on the output and the transfer function depends upon the load impedance, so I'm wondering if resistive loading on the output might be a challenge in shifting the filter down into the audioband.

[Paul Birkeland]

Class D amps, like this one, have a 2nd order filter on the output and the transfer function depends upon the load impedance

Indeed it does.  If one wanted to use the Quicksand for headphone-use only, loading the output with an 8 Ohm L-pad loaded by an 8 Ohm resistor might make for an interesting modification.