Hello everyone !

Last update was about the single ended filters, which i thought we were done with but somehow something really important dawned on me, let me explain :

• Speakers impedances are usually standardized and really low, think 1, 2 ,4 , 8 Ohms. They can therefore be driven really hard (low impedance = high current). As such, they are always in BTL configuration.

• Headphones impedances are not really standardized and rather high (30 Ohm to 600 Ohm). They really don't need that much power to be driven though, usually in the tens of mW.

Here's the kicker, single ended outputs are usually reserved for signal transfer, not for for driving

• RCA for instance is meant to go between a DAC and an amplifier, not an amplifier and a speaker.
• 3.5mm / 6.25mm jacks don't carry the current needed to drive speakers, just the signal etc.

why not use an OpAmp ? an OPA1611 should deliver way enough power without coming close to bottlenecking on noise or THD...

Literally just placing it after the single ended filter should do the trick, no clue how that flew above my head but yeah.

A few design choices remain to be made : 

• should we use the volume control from one of the ICs, or with a variable gain at the OpAmp ?
• is the opamp really load independant for smaller loads ?

Futher testing is required !