Most transparent power amp

Kosst, not to belabor a minor point, but a "passive" electronic device would usually be considered to be one having no "active" components (e.g., transistors or tubes), at least in its signal path. A device which provides zero voltage gain but amplifies current and power is not a passive amplifier, in the sense that George was using the term and per what seems to be generally accepted terminology.

Regards,
-- Al
   

@almarg 
In a strict sense, yes, but passive preamps utilize active components to buffer the input, volume, or both, so that the variation in impedance by the volume control doesn't reshape the response. Generally, so long as the circuit's goal is impedance conversion, it's called passive because it's doing the job of a passive component, namely a transformer. 

kosst

Al's right, the F7 is far from being passive "no active components that the signal passes through"

Cheers George 

Not talking about the F7. 

Sorry I meant F4, the signal still still passes through active IRFP240-9240 Mosfets, so it's not passive, even if it has no gain, it's still active

Cheers George