Originally Posted by germanium
The second sentance is completely false when dealing with tubes. Why? Tubes are high impedance devices in general. There are very few tubes that can drive spealers directly & then only if run in paralell.
Feedback improves measured performance not nessessarily audio performance. You will get the best performance with most tube amps if the output impedance without feedback matches the load impedance. This is true whether you add feedback or not. You will get better measured performance with feedback if you match the impedances before adding feedback. Feedback lowers output impedance as the speaker sees it but the tubes still need the matching impedance before adding feedback to perform best as they see the load.
You have mis-read my second sentence.
Removing feedback does not remove the transformer.
I was not talking about removing the output transformer.
I agree, tubes work best when driving a high load impedance because they have a high output impedance, can output a lot of voltage but cannot output a lot of current.
I agree that in a vacuum tube power amp the output tubes normally drive the primary side of the output transformer which presents a high impedance load to the output tubes.
Feedback improves bandwidth (therefore reduces phase shift across the audio bandwidth), decreases distortion, and decreases output impedance (therefore increases damping factor). It can also improve transient response. Doesn't that improve audio performance?
But the secondary side of the transformer (the output of the transformer) almost always has a much lower output imedance than the speaker impedance.
This is to increase electrical efficiency of the amp, among other things. Transformers are only efficient when secondary impedance is much lower than load impedance.
You will normally get better measured performance too, i.e. higher damping factor.
There are a few SET amps and guitar amps out there where the output impedance is almost as high as the speaker impedance, but those are exceptions.
To say that an amp sounds better without feedback is a very subjective statement.
I think you must have a preference for very coloured tube power amps. Which is fine, I enjoy the sound of a good tube amp as much as I enjoy the sound of a good solid state amp.