[Crazy*Carl]

I heard something that challenged my current knowledge on DAC's and I want to clear it up.

From what I read, there are some dedicated DACs (take for example the Heardroom micro DAC) in which if you plug a headphone directly into the line out, you get a extremely loud sound. I thought that a dedicated DAC (not a DAC/AMP combo) produced a high unamplified signal that would be very low on volume, hence the purpose of an amplifier. What am I understanding wrong? Thanks.

 

[Hybrys]

There are two things that DAC-only devices can output. TECHNICALLY, one has an amplification stage, but the amplification is set to 'line-level' (89 db? Don't quote me on that), and the other is more of a raw signal. The first one, raising the sound to line-level is a DAC with a pre-amp circuit. The other is the same thing, just without said pre-amp circuit.

As for the advantages of having a pre-amp vs a low level signal... Well, I dunno. This is part of the adventure I haven't really explored yet, and I wouldn't be surprised if everything I said is wrong. <_<

 

[Crazy*Carl]

Anyone else have an idea?

 

[joe_cool]

Most modern DACs use an output circuit which delivers about 2VRMS. This is the only way to get >100dB dynamic range since a 1K ohm resistor will generate about the same noise. That doesn't mean they will drive a headphone with any quality; the analog outputs are good for about 600-2000 ohm loads, not 32 ohms like most headphones.

 

[Crazy*Carl]

So with that it almost seems a headphone amp is a deamp.... this doesn't make very much sense.

 

[joe_cool]

The explanation is that most headphones will play very loudly with 1-2 volts input, but this will require about 50-100 ma of current which very few DACs will supply. E=IR

 

[Crazy*Carl]

Quote:

Originally Posted by joe_cool /img/forum/go_quote.gif The explanation is that most headphones will play very loudly with 1-2 volts input, but this will require about 50-100 ma of current which very few DACs will supply. E=IR

Ah, so your saying a DAC will give the amp lots of volume, but with low current and hence poor sound quality?

 

[joe_cool]

I think you don't understand the implications of Ohm's law (E=IR). This is a linear relationship with three variables. Loudness is proportional to power which is E-squared/Resistance or Current-squared*Resistance. Just because the DAC has the potential to deliver 1-2 volts doesn't mean it will when the impedance (resistance) is too low for the DAC's circuitry (the load requires too much current).

 

[ROBSCIX]

If the Dac has no dedicated amplifier output then you are just dealing with normal line level signals. Provided your headphones are not high impedance the line out would drive them. As to what quality though is the question. Many will suggest a can amplifier for any headphones and other suggest them for mainly high impedance cans.

 

[m1abrams]

Also if a DACs output is designed to expect a high impedance load its coupling caps will not be sufficient with low impedance load and will cause a significant loss in low freq. response.