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Negative Feedback - Call for Opinions

77.43.10.3
Posted on October 16, 2009 at 00:40:02
6AS7_6SN7
Audiophile

Posts: 98
Joined: September 10, 2009
 I have designed, built and tested several tube amplifiers (from 4W to 40W, OTL, PP, for hi-fi and guitar, all with global feedback applied over 2 or 3 stages).

In my experience I have always found that some global moderate feedback helps to get the best overall performance of a tube amplifier (I mean with the particular speakers that I use in my listening room) and to stabilize performance against components ageing.

However I see in the asylum that there are different opinions about the use of negative feedback.

Many inmates are quite strongly convinced that the quest for zero feedback is a must for every serious audiophile.

This is the reason why I propose this call for the survey of the opinions (and or the experimental findings) of all the interested inmates.

A speculative byproduct of this survey might also be the definition of some novel measurement technique able to better correlate laboratory measurements with the results of live listening sessions.




ecc230
NFB is needed for imperfect speakers., posted on November 18, 2009 at 10:57:08
kurt s
Audiophile

Posts: 68
Joined: October 12, 2009
 If the speaker load isn't a perfect flat 8 ohms, without resonances and especially has areas of capacitance, then the amp has to fix it up with a band-aid to cover the weakness of these speakers. That would be NFB.

A perfect speaker would also be linear and need 1 watt of power for maximum needed volume to keep an amp linear without NFB. Well the speakers are usually not that good, yet some very costly horn systems do approach this ideal.

So what do you want to compromise on? An amp that's compromised and fits poorly designed 2 ohm minimum impedance compromised speakers and buy both compromised components, or an amp that's almost ideal with speakers that are almost ideal and buy both. It takes years of experimenting and spending vast dollars to understand this concept, and then only to find nothing is really perfect as something is always flawed. :-)

-Kurt

RE: Negative Feedback - Call for Opinions, posted on November 15, 2009 at 10:20:36
shermanr@prw.net
Audiophile

Posts: 497
Location: Sunny San Juan, PR
Joined: June 8, 2004
Contributor
  Since: June 24, 2009
 I enjoy committing audio heresy myself and have done so by applying Feedback to my DIY 2A3 Single Ended stereo amplifier.

A little bit of global feedback on this amp was able to tighten up an otherwise bloated and pretty poor Bass performance.

Just like too much of anything is bad for you, a little feedback properly applied can improve the measured performance of an audio circuit.

Yet some critical ears seem to get annoyed by the use of Feedback if it is really not necessary.

Like a spice, feedback is only a part of a larger whole. The end results seem to indicate that it's not the villain some claim it to be.

RE: Negative Feedback - Call for Opinions, posted on October 16, 2009 at 07:43:59
shermanr@prw.net
Audiophile

Posts: 497
Location: Sunny San Juan, PR
Joined: June 8, 2004
Contributor
  Since: June 24, 2009
 You should do a search for this. As a topic, this one has been thoroughly discussed in the Asylum.

I got your message!, posted on October 21, 2009 at 00:43:48
6AS7_6SN7
Audiophile

Posts: 98
Joined: September 10, 2009
 After reading many of the past posts on the subject (most of them are more than 5 years old) I understand why no one will likely expose again himself by repeating his opinions on this matter.

Once you had get burned by hot water you fear cold water as well.

It clear to me now that the feedback/no-feedback clash will go on forever (unfortunately with no benefit to the open minded audiophile).

I have realized that the research for some better experimental technique for correlating the results of subjective listening to the quantity of feedback applied to a particular tube amplifier has been blocked by the vendors lobby who are not interested in the possible scientific results but rather to use the feedback argument as a sales tool only.

All audiophiles should oppose to this status of things and I will certainly do.

ecc230

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