Negative feedback, voltage and output impedance

All,

Thanks for the replies.

If I understand this correctly, if I want to buy a high power (voltage for ESLs) tube amp with low output impedance and low or no negative feedback, then I need to look at OTLs, correct?

Thanks.

Mike

The term "negative" is unfortunate. It really should be called "corrective" feedback. It corrects various forms of distortion and frequency response deficiencies, but if used to excess can introduce its own problems.

The amount of feedback is always user adjustable, if the user has a soldering iron. I went through a stage of feedback tweeking, but eventually decided that the designer always got it about right. Why would he do otherwise?

Among tubophiles there is a tendancy to conveniently forget the significant feedback provided by the ultralinear windings of the output transformer which are applied directly to output tube auxillary grids.

Hi Marakanetz,

Just FWIW, as a manufacturer I have to be careful what I say as this forum is moderated. At the same time what I am expressing is actually the way I see it and that has served me pretty good so far for the first 26 years or so anyway :)

I hope you don't consider it a sin that I try to walk what I talk. OTOH, our early amps for the early 80s did use feedback, so its not as if I've not given it a fair shake. Every now and then we re-try some of the stuff we abandoned, just to see if we are still on target. FWIW, amps without feedback are harder to set up as you have to be more careful about the speaker choice. This means our market is probably a bit more limited. As a result it doesn't take the ability to download and chew gum at the same time to figure out that I'm not in it for the money...

Another difference between us and Mac is that our warranty is transferable and we will reactive that warranty on any product that we have fully updated.

Negative feedback aka "error correction circuitry" is kind of like trying to bail water out of a boat that has a major leak. Plug the hole i.e. build a linear circuit first, then worry about corrective measures later ( if needed at all ). After all, you can't respond to an error until it's already happened, making error correction introduce it's own errors due to the lag time involved. As such, designing the circuit for maximum speed and linearity negates much of the need for such "band-aids" as feedback. This is because the circuit is both fast and stable enough to keep up with any of the demands placed upon it without introducing its' own non-linearities into the equation.

As a side note, high levels of negative feedback is what makes a large percentage of SS designs sound hard and sterile. Most of the SS amps that offer excellent high frequency "air" while retaining midrange "liquidity" are of a low or no feedback design.

For those of you that have never heard a low / no feedback SS design that is fast with wide bandwidth, i would suggest checking it out. For those that have never heard an Atmasphere OTL amp with suitable speakers, i also suggest checking that out. Both of these types of products are what "accurate musicality" sounds like. Sean
>

How can there be a ss amp without ANY feedback?? I.e., Isn't some local feedback necessary?
I'm not savvy on these subjects: which can explain my stupid question:)