I didn't find a defused picture of this device(apogee symphony i/o mkII).,So is there someone could say something about"constant current drive headphone AMP"?
They appear to be describing a transconductance amplifier. Voltage-to-current (high output impedance), rather than the usual voltage-to-voltage (low output impedance). AKA, current-drive, as well as by some other names. The output current is dynamically constant. Meaning, it changes with the input signal, but does not change with impedance variations in the load. Nothing new or innovative about these, so it's not readily apparent what is "unique" about Apogee's design, as they are stating.
There are current-drive amplifier project threads here on the diyAudio site. For example, Joe Rasmussen's simple to build chip-amp based current-drive amplifier thread.
There are current-drive amplifier project threads here on the diyAudio site. For example, Joe Rasmussen's simple to build chip-amp based current-drive amplifier thread.
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Thank you for the answer!
Especially you mentioned about a chip based solution. I used to considering"maybe it is just current drive", but I think it can not be built by purely chips and apogee are unlikely to use desecrate parts.
Especially you mentioned about a chip based solution. I used to considering"maybe it is just current drive", but I think it can not be built by purely chips and apogee are unlikely to use desecrate parts.
Take a look at the Joe Rasmussen thread I'd mentioned. It does require some passive components. The same passive components you would need for implementing an op-amp based circuit, which is what it essentially is. See link below.
https://www.diyaudio.com/community/...tt-transconductance-current-amplifier.239321/
Joe’s is a version of Duo’s variable transcondicutance amp. Uses a pot instead of an R in the feedback loop (as i understand it) to allow for changing the output impedance from near zero to near infinity. Very eyeopening and a VERY nice sounding amplifier. Used teh first generation diyAudio LM3875 gain-clone board.
Current amplification, and nea rcurrent amplification are really just startint to be explored (again) and some very intersting results are coming.
dave
Current amplification, and nea rcurrent amplification are really just startint to be explored (again) and some very intersting results are coming.
dave
This thread contained a lot of useful imformations of current drive HPAs.
https://www.diyaudio.com/community/...per-linear-transconductance-amplifier.328449/
https://www.diyaudio.com/community/...per-linear-transconductance-amplifier.328449/