High-End Tube preamp with ECC88

[Shoog]

Originally Posted by SY

I suppose this is easier than providing actual, you know, data.

Maybe you and DF96 would furnish us with a detailed analysis of why the F5 and nelson Passes other top end offerings are not as good as your high feedback designs.

I have personally compared a RLD to a F5 and there was no contest, the F5 is fantastic, the RLD sounds like a generic feedback amp. Of course thats just my personal experience. However my friends RLD went into storage and the F5 is his standard amp after that. The builder never scrimps on parts choice in whatever he builds, so I am certain the RLD was giving of its best.
After this experience I started treating your opinion with a large pinch of salt.

Shoog

[DF96]

You, like everyone else, may safely ignore my opinions if you don't like them. You ignore truth at your own cost. I don't trust my own ears, so I certainly don't trust yours.

[SY]

Indeed, not everyone wants an amp that's neutral.

[popilin]

Originally Posted by Shoog

I have not really considered the underlying reasons for why more gNFB sounds worse, I am simply reporting my personal experience.

One of the oft quoted reasons is that as low order harmonics go down, high order harmonics go up, and gNFB causes this. The human ear is exquisitely fine tuned to these high order harmonics. Phase shift issues seem to play a large part also.
Fundamentally though it is important to remember that THD measures are fairly inadequate at characterizing what is really going on in any given amp as there are multiple other influences on the sound.

This is an interesting article which expresses what seem like reasonable opinions. It highlights the advent of the Williamson design as the cause of the popularity of gNFB which absolutely needed copious gNFB to work;

The Numbers Game

Shoog

Looks like I got a little late.

BTW. The higher the harmonics, the lower times involved, so NFB is less effective on higher order harmonics because of the impossibility of the travel to the past.

NFB Math don't include relativistic corrections.

Not to mention that conductors aren't perfect, and we work with valves, capacitors...

I escape to NFB like the plague.

[Shoog]

Originally Posted by DF96

You, like everyone else, may safely ignore my opinions if you don't like them. You ignore truth at your own cost. I don't trust my own ears, so I certainly don't trust yours.

Its a dangerous place to be when you are prepared to stand against everyone in expressing a theoretical position over their personal experience. No one here is advocating shoddy high distortion designs and they go to great lengths to achieve this without resorting to gNFB.

I personally use input transformers, DC coupling, Low Mu triode, balanced designs operating in pure class A with plate to grid feedback. That's a lot of careful design decisions which have gone into my position. Have you built such an amp to compare to one of yours ? Do you have enough experience to make an informed comment on what can be achieved in zero global feedback designs ?

I suspect you are a well trained engineer who "knows what works", allow me to differ with that position.

Shoog

[Wavebourn]

Originally Posted by SY

We're talking about preamps here. Overload in power amps driven to clipping is a different story, thus the rather elaborate measures I used in my power amp to minimize recovery time, or your soft clipping circuits.

Williamson was just an example. I don't hesitate to squeeze the maximum from 2-stage designs when I permit myself to. But with 3-stage design (if I decide that it is needed) it is very interesting game to fond the optimum. Sometimes it takes an year before I give up.
But I always tend to use nested feedbacks with more than 2 stages. Nested feedback is more than a sum of feedbacks. It is like a duck's triangle migrating, compared to a single duck. And please don't tell me the theory that synapses in duck's heads in triangles are wired all together!

Precisely. As with any other aspect of circuit design, if you don't understand it, you're likely to get a bad result. Some attribute it to the design element rather than their own inability to understand and use the tool properly.

It depends, "properly". Properly for the end result you wish, or properly for the accepted standards of measurements?

[DF96]

I am not standing against "everyone", just those who claim that gNFB is a bad thing. As Wavebourn says, the real issue is understanding what it can do and how to use it properly.

Most music is, and almost always has, been recorded using systems which use huge amounts of feedback around op-amps. Fortunately, most of this kit was designed by people who knew what they were doing. Note that any feedback around an op-amp is global, not local, because the op-amp has several stages. If this adds something nasty to the sound then nothing you can do at home will remove it. Therefore it is likely that it does not add nasties.

[Wavebourn]

Originally Posted by SY

Indeed, not everyone wants an amp that's neutral.

I feed the people on the last BAF by a neutral PA. It seems to me they liked it. I mean, they liked that they heard people well, instead of hearing the PA.
Let's try the next year to make more neutral PA and see what people say.

[SY]

Originally Posted by Wavebourn

Properly for the end result you wish, or properly for the accepted standards of measurements?

These are not mutually exclusive unless you have an unusually crabbed definition of "accepted standards of measurements."

[Wavebourn]

Originally Posted by SY

These are not mutually exclusive unless you have an unusually crabbed definition of "accepted standards of measurements."

No, my personal tastes are far from them.