Effect of high output impedance from source?

[Sentral Dogma]

What is the effect, sonically, of the output impedance of a DAC/source? I get the impression that it effects bass or something? Similarly, what does a low output impedance do?

Thanks

 

[JaZZ]

A high output impedance, let's say 1 or even 2 kOhm, normally doesn't affect sound quality -- in view of the input impedances of pre-amps and headphone amps, which are located in the 25-60 kOhm range.

 

[Carbonman]

Quote:

Originally posted by JaZZ A high output impedance, let's say 1 or even 2 kOhm, normally doesn't affect sound quality -- in view of the input impedances of pre-amps and headphone amps, which are located in the 25-60 kOhm range.

your response doesn't deal with the question of the relationship of high output impedance at the amp to headphone impedance. I'm wondering if the frequency response of a headphone will change as the amp output impedance approaches the input impedance of the headphone. This sort of change in frequency response occurs with loudspeaker; shouldn't it also have an impact on the headphone listening experience?
BTW, can anyone tell me who makes head amps designed to drive high impedance headphones?
Cheers,

Graham

 

[Wodgy]

For preamps, a moderately high output impedance shouldn't make a big difference. If the output impedance is too high (above 10k), however, your system will be much more susceptible to picking up RF/EM interference, and you'll need to be careful to use well-shielded cables. Also, with such devices, it's wise to make the interconnects as short as possible, because you risk having high frequency rolloff from the capacitance of the interconnects.

With headphone amps, you want an output impedance less than the headphone's impedance. The damping factor of an amplifier is given by headphone impedance / amplifier output impedance. Generally larger damping factors give better control over the bass. The output impedance of an amplifier may also affect the frequency response of the headphones. For more info on that, see the article on the Meier Audio website.

 

[JaZZ]

Quote:

Originally posted by Carbonman I'm wondering if the frequency response of a headphone will change as the amp output impedance approaches the input impedance of the headphone.

If a headphone has a linear impedance response, a high serial resistance (output impedance) doesn't affect its frequency response. Grados have an astonishingly flat impedance curve, so they aren't too sensitive to high output impedances despite their low 32 ohms. Anyway, a serial resistance of 32 ohm will slightly pronounce the bass resonance (which is combined with an impedance hump) around 100 Hz. Other headphones have less linear impedance responses and logically are more susceptible to frequency-response degradations due to serial resistances. In all cases the rule-of-thumb applies: the higher the impedance within a driver's impedance curve, the lower the attenuation caused by a serial resistance.

 

[Budgie]

The higher the output impedance of the source, the more likely you are too have problems from cable capacitence. It usually shows up as loss of treble definition.