DAC/Amp Impedance Matching?

[solderdude]

so even if the output impedance of a DAC is nearly 0 ohm, there would be no difference to the same DAC design was with 500 ohms of output impedance

Yes, but DAC output resistances will not be near 0 ohm, only headphone out and speaker out will be.
To prevent issues with cables etc. the output R of a stand alone DAC (only) will usually be higher, in the order between 50 and 100 ohm or so..

In the thread the 'DAC mode' simply is volume at max. In principle it has nothing to do with output R of the device but everything with an 'assured' high load resistance.

 

[DeepSpace57]

Yes, but DAC output resistances will not be near 0 ohm, only headphone out and speaker out will be.
To prevent issues with cables etc. the output R of a stand alone DAC (only) will usually be higher, in the order between 50 and 100 ohm or so..

In the thread the 'DAC mode' simply is volume at max. In principle it has nothing to do with output R of the device but everything with an 'assured' high load resistance.

I think DAC mode changes the output impedance of 9038D (makes it around 300 OHM).

What I mean is he claims not to have the impact of bass (low ends) as the output of 9038D is pretty low like 0.3 OHM. There seems to be making some senses for me because DAC designer does not do any rally about how less output impedance of the line-outs is designed.

I also lost the bass impact of 9038s after using it as a standalone DAC.

 

[solderdude]

The load (amplifier input resistance) is resistive so bass cannot possibly change.
Even when the output resistance changes from 0 to 300 ohm and the load of an amp is 10k the input voltage would drop 0.2dB across all frequencies.

You could ask the designer @IVX (who is a member here) if the output resistance changes between modes and if so the reason for it.

 

[MusicNBeer]

Many amplifiers run a shunt cap in the 200-400pF range to reduce RFI. This makes the input impedance drop with higher frequency. So an abnormally high output impedance device, say a 50K pot on a passive volume control, will attenuate high frequencies a bit as well as reduce output. Ironically this frequency attenuation effect is slightly greater when the amplifier input resistance is higher.

 

[DeepSpace57]

Many amplifiers run a shunt cap in the 200-400pF range to reduce RFI. This makes the input impedance drop with higher frequency. So an abnormally high output impedance device, say a 50K pot on a passive volume control, will attenuate high frequencies a bit as well as reduce output. Ironically this frequency attenuation effect is slightly greater when the amplifier input resistance is higher.

So, if we use a DAC with extremely low output (feeding a regular external amp), do we have a `frequency attenuation effect` at the end?

what is the reason why DAC designers do often make up 300-around ohm as Line out? If lower is better, why not is it 1 ohm or less?

 

[MusicNBeer]

what is the reason why DAC designers do often make up 300-around ohm as Line out? If lower is better, why not is it 1 ohm or less?

This only happens in reality with REALLY high output impedances, like the 50K pot that has an output impedance of 12.5K at -6dB from full output. I have first hand experience buying a 50K pot then noticing highs rolled off at high volume.

Devices can't make output impedance too low or the output stage will blow out as soon as it's accidently shorted, say when plugging in RCA to amp with DAC output on.

 

[solderdude]

what is the reason why DAC designers do often make up 300-around ohm as Line out?

The reason is often the output current limit of the output driver (usually a low power opamp). When the designer adds a resistance then any load it sees will not be able to affect performance nor throw off the overall feedback loop. Such a resistor acts as an 'isolator' so unusually high capacitance interlinks and very high load impedances cannot cause any problems. Most opamps have no issues with loads > 600 ohm.

Low load resistances of amps connected to DAC outputs (and I mean 600ohm inputs or so) can possibly cause audible low roll-off when the DAC as an AC coupled output (capacitor in the output path).