Negative Feedback a deal killer?

Hello Athmaspere,

I have received reply from John Ulrick of Spectron - their chief designer. I sent him your first post as well:
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"The above comments are only relative to analog circuits. It’s true that negative feedback in slow circuits with a –Z term in their transfer function have inherent ringing and do not enjoy the benefits of negative feedback. Spectron’s forward loop does not have any analog circuits, it’s digital with a propagation delay of .2uS. Engineering requires quantitative analysis. The first order look reveals some insight. Applying super-position theorem: The period of a 20KHz sine wave is 50uS. The ratio of the wave period to the forward loop propagation delays is 50uS/.2uS = 500 In simple terms, this means that the control loop can imitate 500 control vectors at shortest wave period of the input function."
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Now, if you look midrange then the ratio would be about 5000:1 and for the bass 50000:1. So, while you are correct (in your 2nd post) that fast feedback is still not in real time - I would submit to you that in practical terms you can call it "nearly real time speed" it so fast!. While John mentioned here that the control loops used in Spectron are not analog but DIGITAL - you can read it in much greater details on Spectron web site.

I will not work as a mailman here anymore - if you want to discuss NF with John or Simon - take it to them, directly.

Cheers,

"50us/0.2us = 500" ?

Dob, have you ever heard or checked out the H2O Audio gear? His amplifiers are not slap-an-ICE-module-in-a-box affairs. They have very stiff linear power supplies and they sound different from other ICE module amps. His preamplifier has, as far as I know, a very unique design resulting in extremely high quality sound. While subjectively one can like or dislike his products, objectively, he is a skilled and knowledgeable designer.

Regarding negative feedback, I agree with most other end-users who have posted in this thread. In my experience, some amps that advertise no negative feedback sound very good when driving speakers that offer a benign load, but tend to sound soft and rolled off when driving more difficult speakers. While having auditioned and owned gear from a number of good designers, I've had better results with electronics that have some amount of feedback when driving my particular speakers (Avalon Opus).

By the way, I've heard the Spectron amps as well and I thought they sounded good in the two systems I heard them in.

Alan

Aljordan,

In my post I expressed NO JUDGMENT of the sound of H2O and other amplifiers which use B&O ICE Module whatsoever. I knew in moment I will do it people like you will attack me and I like to be attacked exactly the same as next guy. If you still feel offended then my sincere apologies - we really talked about differences in designs and their effect on even/odd order of ditortions as well as capability to drive difficult loads.

"...they sound different from other ICE module amps"

Here, I must take issue this this statement. Firstly, if linear power supplies used are BEEFY then most certianly this amplifier will have better dynamic range then all others based on tiny switching power supplies (again - huge exception is Jeff Rowland). So here I agree with you but in regard of the dynamic range only.

Secondly, if your amplifier is reasonably neutral and B&O modules certainly are then any change (say in PS wire or input capacitor) will produce somewhat different texture, so obviosuly each of them will sound slightly different but their main sonic signature is determined by their input/output stage...which are identical or nearly indentical (with some mods) in all of them.

Cheers

"better dynamic range then all others based on tiny switching power supplies (again - huge exception is Jeff Rowland)"

Not only that most (if not all) of Rowland Icepower amps use SMPS supplies but he uses them as well in Capri preamp and new generation of class AB amps. Rowland amps like 102, 201, 501 use standard B&O modules with built in SMPS.