jandidden

Responses from jandidden

Tube Amp for Martin Logan Speakers
So, to recap, what did we learn:- output impedance of a 'box' is *defined* as the change in output voltage divided by the current change that caused the voltage variation; - nfb makes the output voltage change smaller for the same current change, ... 
Tube Amp for Martin Logan Speakers
My 2nd post above, where I say: 'The Iload is therefore 0.5 amps' should be of course 1 amp (from 8 V across 8 ohms). Duhhh. :-) 
Tube Amp for Martin Logan Speakers
Atmasphere, I read your last post again - are you trying to say that even when nfb decreases the voltage drop due to increased current output (the Zout), that doesn't mean that the amp can all of a sudden deliver more power? If so, I fully agree. ... 
Tube Amp for Martin Logan Speakers
Atmasphere, your conclusion that someone (certainly not me!) would think if you lower the Zout to zero in a preamp, it can effortlessly drive 4 ohms, is rather far-fetched. As I'm sure you know, Zout has NOTHING to do with what you can or cannot d... 
Tube Amp for Martin Logan Speakers
George don't make me blush :-).Anyway. Atmaspere's statement that the INTERNAL Zout doesn't change has another side to it. It suggests that you can open up an amp and point to a component and say see, there's the output impedance. This is not the ... 
Tube Amp for Martin Logan Speakers
Bifwynne, if I may, not trying to split any hairs, but the term SOA has a very specific meaning for ss devices. The Safe Operating Area defines the combinations of current and voltage across the device, that it can withstand for a certain time bef... 
Tube Amp for Martin Logan Speakers
Byfwinne, yes I agree. The internal amp Zout is not changed of course.Re: increased 3rd with nfb: that has been laid to rest many years ago. Most people know the (in)famous Baxandall graph showing increased harmonics (even harmonics that were not ... 
Tube Amp for Martin Logan Speakers
Output impedance does go down with nfb - that's a basic tenet. Easy to check: take a non-nfb amp and change the load dfrom 8 to 4 ohms. You will see that the output voltage drops a bit. Now apply nfb, do the same thing and you will see that the dr...