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Re: Driving headphones at high peak levels

Bob, that's a very interesting and thorough analysis, but the weak point of the sound card you recommend seems to be the low-frequency response.

The 2 ohm output you refer to is labelled "line out" in your document, so doesn't that suggest that it's designed for driving high impedance loads? If so, there's probably a decoupling capacitor on the card's output, attenuating low frequencies, even when driving a normal (high) line impedance. This seems to be confirmed in your frequency response graphs.

Driving a lower load impedance (e.g. headphones) will decrease the time constant associated with the capacitor and make this defect extend to higher frequencies.

Or am I reading too much into the graphs?

Steve Beet

On Mon, 8 Dec 2014 08:58:13 -0500
Bob Masta <audio@xxxxxxxxxxx> wrote:

> > Choose a USB sound card with "better" specifications The
> > USB sound cards that I have seen have output impedances
> > of around 50 ohms or higher, making them unsuitable for
> > driving low impedance phones, so a low-output-impedance
> > USB sound card with decent maximum output would be one
> > solution 
> I have tested several USB sound cards.  The hands-down 
> winner for low output impedance (2 ohms) can deliver nearly 
> 1.5 Vrms into 100 ohms.  I especially like it because it 
> has no hardware controls on the unit that can get 
> accidentally changed in a lab setting.  It has pretty good 
> specs in most other respects as well.  See
> the Comparison Table under "Sound Card Perfomance Tests" at 
> <http://www.daqarta.com/dw_gguu.htm>