Tube amplifiers: distortion & coloration or transparency & realism?

You are not considering variable feedback, I run my amp at zero feedback.

 

My amp designer friend says high impedance valve amps into passive crossovers can exacerbate opacity.

 

I consider Pass and others to be "commercially popular" - in terms of the audiophile market anyway. Is this a forum for mass market stuff? Not if it's concerned with the best sound quality.

 

What does that even mean, precisely?

 

I think that all Burt's saying, in response to what I was trying to say, and in response to what may be a common perception like this:

is that most amps you come across -- tube or solid state -- use global negative feedback: most solid state amps hifi and most hifi tube amps designed after the '30s.

No doubt in the contemporary audiophile world you can find all kind of designs available from builders, or as DIY and kit products, offering all sorts of different circuit topologies and people have myriad choices. But if there's a general impression that SS= global NFB and tube = no global NFB, that's not really so, and many of the sonically cherished tube designs of hifi's golden age used global NFB.

I know there's a lot of almost-religious conviction out in hifi land about the paths to audio truth -- it only comes through Class A design, or no-NFB design, or analog playback, or digital playback, or whatever. From my POV, everything in audio is a compromise, nothing's perfect -- not flea watt triode amps through high-efficiency horn-loaded speakers, not Class A or Class AB or Class D amplification, not dynamic loudspeakers, not dipoles -- everything has its strengths and weaknesses. We audiophiles as a group tend to get really reductive and absolute: "It's all about the NFB and zero is the only proper amount for good sound" or whatever. I'm not of the opinion that any one path, and certainly no one element in a circuit design or signal chain, is primarily the thing that inherently gets us closer to better sound.

 

Not at all. I was reading about negative feedback, and the article said it was developed because transistors were not linear and stable. Tube amps can use NF or not, depending. Mine does. I was not aware that any SS amps didn’t use it, but now a few have been mentioned. I suppose when a SS amp comes up with tube like distortion figurers that it is probably not using NF.

 

I actually think it was phone line engineers in the '20s who cooked up negative feedback to reduce distortion in amps.

 

Quite right.

 

Goes back almost to the dawn of electronic amplification itself.

 

Nelson Pass is a well received designer with decades of experience and he has published a huge number of tech articles and his commercial projects have been received well, but I think Threshold was the last thing he did with any appreciable build quantity. His current products are very esoteric and high dollar, I think volume is pretty low.

His tech articles are worth reading.

 

He's right, but you have to consider that the passive speaker crossover is by its nature the weak point of any playback chain. The problem is that the alternatives are unpalatable to the consumer playback domestic market-either a closed pre-engineered system or some real design work and testing applied to each install.

 

Closed pre engineered 8th order analogue cross over with active newer cleaner active drivers is their aim
Ive heard em
They are very good.

 

I run tubes all the way into Zu Def 4s. Basically full range drivers, first order crossover, simple resistor/capacitor to the tweeter with a built in active sub. Believe it or not had to fight brightness. Tweeked it out with tubes, 5751s in the Macintosh MC 60s and Aperex 6922s in the BAT Phono pre. Very sharp well defined and immediate. Got some Grover interconnects from the Phono Pre to the Line stage and I ask myself how could I want better? So it is all system dependent. Nothing slow about the tube stuff, at all. Not warm, not shrill. I'm very happy.
Getting back into it after 30 or so years I'm astounded at the SQ available today, for a price of course. But the MC 60s sound good.