The best phono stage out there?

Hi Ecka, active phono EQ works inside a feedback network in the phono stage (the feedback takes a bit of the output signal and feeds it back to the input). Because the signal propagates through the phono section at a very finite speed, the feedback is always running a little behind the actual signal itself- in effect it never arrives back at the input in time. This problem is not so bad in the bass region, but in the highs it contributes to ringing in the phono stage. Pops and ticks are the sort of thing that will thus become more noticeable if your phono section employs loop negative feedback.

Loop feedback is known to reduce distortion overall, but at a price- at actually enhances (although in trace amounts) certain odd-ordered harmonics. The trouble is that our ears use these harmonics as loudness cues, so quite often loop feedback contributes to brightness or hardness in the phono section, while on paper the specs appear to be quite good.

Balanced differential operation offers several advantages- of course the cartridge itself is balanced, so you can accept the signal in the balanced domain and get less noise and artifact from the interconnect. But balanced differential operation is also lower distortion because distortion is canceled at every stage throughout the preamp. It also can be lower noise. I like to use tubes as well since tubes can operate without loop feedback, and what I found is that if you really want tubes to be quiet, balanced differential is an excellent way to go.

Of course I use our preamps (either MP-1 MkIII or MP-3) in my system- I use both the ZYX Universe and the Transfiguration Orpheus, both exceptional low output cartridges.

The Best Phono Stage Out There?

Is the one that has you listening to the neglected and almost forgotten Lps in your collection and everything in between.

Ralph's assertions are not entirely correct. While there may be a propagation delay associated with feedback, if the designer knows what he is doing, global feedback can remain useful in circuits that operate in the hundreds of MHz, which is far, far, far higher than anything we can hear.

It is also true that global feedback can enhance certain harmonics, but it should also be pointed out that this is related to the amount of feedback applied. Ergo, altering the amount of feedback will in many cases solve the problem, and that may sometimes entail less feedback, sometimes more.

I have designed multiple phono stages, some with feedback, some without. My experience has been that different circuits benefit from different amounts of global feedback, and that the designer should use his ears as well as as measuring tools to determine the correct amount of feedback. Sometimes the proper amount is 0dB, and sometimes the proper amount may be 60dB. It depends on the circuit topology and how it is built (and in some cases what the operating environment is like).

For the non-engineer audiophile, I would recommend forgetting the preconceptions and using your ears to decide whether a given phono stage is a good one or not.

I would say that the technical capabilities and aesthetic sensibilities (including hearing abilities) of the designer play a much bigger role in successful phono stage design than what kinds of technology that it uses.

hth, jonathan carr

Jcarr, while I agree with most of what you have said, and I also feel that its a bad idea to make generalizations, especially in **this** sport, I can safely say that I have yet to see a decent circuit where feedback was also a good idea. Certainly I have seen and worked on many circuits that I consider less than ideal; many of them would not work at all without feedback. Nor would they sound right.

My comments are really aimed at the state of the art, which IMO is going to have to do when we talk about the 'best' :) In that context we may have a difference of opinion, but I'm stick'n to my story: feedback violates the most important rule of human hearing, our perception of loudness. Thus a designer uses it at his/her own peril, as it will be an influence that steers the electronics away from sounding real, and towards sounding like a hifi.

Ralph, of course I was including state-of-the-art, award-winning designs. Of course.

I invariably dial in the amount of feedback that I use by ear as well as meter, and sometimes the result is more GNFB, sometimes less (or zero).

FWIW, when a circuit sounds like it has too much GNFB, to my ears the sonic problems tend to manifest themselves as dynamic compression and timbral shifts in a decidedly unnatural direction, as well as spatial flattening.

My general experience has been that using GNFB to try to turn a poor-sounding circuit into something decent rarely gives acceptable results. A design that sounds good with lots of GNFB (global feedback) tends to sound pretty good without it, too.

So while I think there are similar aspects to our respective standpoints, Ralph, we'll just have to agree to disagree as to the usefulness of GNFB for SOTA audio.

As an aside, I've auditioned some highly-regarded commercial zero NFB designs that I liked and admired a lot (yours among them), while others (some also highly regarded) have left a different impression.

For example, perhaps two months ago, I had a chance to listen at length to a high-feedback preamp design of mine from the late 1990's, Charles Hansen's zero NFB KX-R preamp, and a contemporary highly-regarded European-made zero NFB preamp. It was my opinion as well as others who heard these same pieces that Charles' zero-NFB KX-R and my high-GNFB design sounded a lot closer to each other than either did to the European-made zero-NFB preamp (which FWIW sounded much more "contrived").

I stand by my opinion that the individual designing the product has a far greater effect on the sound than whatever technology that he happens to choose.

best, jonathan carr