Quote:
Originally Posted by jslevin  I don't know how that can be the case. The monitor and headphone outputs always share the same signal, because there's only one DAC pair, yet they can be running at different levels. How is that possible, unless both stereo attenuators are post-DAC, which would make them analog controls?
I believe the Duet provides essentially an analog attenuator for monitor control.
JSL |
The two outputs can't be run at different levels. Lots of people have been moaning about just this issue. Sure the absolute levels are different, but the difference is fixed, simply due to the different gain of the output driver and headphone driver amps.
To quote from the Apogee Duet FAQ:
Apogee Electronics: Products: Duet Quote:
Q: Can I set the headphone and line outputs to different levels?
A: The headphone and line outputs are always controlled simultaneously. To set the balance between headphones and speakers connected to the line outputs, set the speaker’s amplifier accordingly. It is possible to mute the headphones and line outputs independently.
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There is nothing between the DAC and the output. It goes CS 4272 (DAC), LM833 (I/V converter) LM833 (output op-amp) . Both outputs add a few of bipolar transistors on the end of the op-amps to give them additional drive, and a mute, but that is it. The CS 4272 internally provides a digital domain 20 bit attenuator before the DAC for output volume control. That is all there is.
Input level control is done inside the PGA2500 mic amp chips, and occurs before the ADC. (In addition there are 10dB relay switched pads that extends the input gain range.)