Trying to understand the “Global feedback in amp design “ I came across this.
I am now even more mystified.
Is there a layman’s version to explain this?
Objectivity vs Subjectivity
- Thread starter Passive_audio_enthusiast
- Start date
I am now even more mystified.
Is there a layman’s version to explain this?
Seems to be the same as negative feedback
I think @IndianEars ears had posted not too long ago on how Negative feedback can be used to reduce distortions and are also (mis)used to show very low distortions in specs but at the expense of sound when you hear it.
In simple terms, a part of the output of an electronic circuit is fed back to the input to change the characteristics of the output, mainly to reduce the gain of the circuit and to linearize the response.
Yes. I meant global negative feedback. High anoints of that make the spec sheet look good and also increase the damping factor - but - IMO - suck the life out of the music.
I wonder if it is second order harmonics that actually provide timbral cues. Single ended tube amps have a lot of this and do much better here - push pull tube amps with negative feedback measure well but also lack that magic. So it isn’t tubes per se.
It would be interesting to make a zero feeeback solid state amp and see how that sounds.
I wonder if it is second order harmonics that actually provide timbral cues. Single ended tube amps have a lot of this and do much better here - push pull tube amps with negative feedback measure well but also lack that magic. So it isn’t tubes per se.
It would be interesting to make a zero feeeback solid state amp and see how that sounds.
A post by Nelson Pass gives some idea.
Since this actually reduces distortion I presume the gain of the amplifier will need to be reduced quite a bit and that impacts the drivability of the speaker most of the First watt amps vary between 11-20 dB and claim to be zero feedback .
Even for my relatively sensitive Tannoys I need at least 32-35 db of gain across pre/power to drive them. Even a 26 db amp was having a problem until I put in an active preamp.
keith_correa
Well-Known Member
I quote from Bruno Putzeys:
"Nobody with a solid working knowledge of feedback theory chooses to avoid it. “I choose to avoid feedback” is an all too transparent code for “I’ve yet to figure it out”. Perhaps the biggest myth surrounding feedback is that it is a quick and easy fix. It isn’t. Feedback is a fascinating and complex topic that lies at the core of successful design."
"Nobody with a solid working knowledge of feedback theory chooses to avoid it. “I choose to avoid feedback” is an all too transparent code for “I’ve yet to figure it out”. Perhaps the biggest myth surrounding feedback is that it is a quick and easy fix. It isn’t. Feedback is a fascinating and complex topic that lies at the core of successful design."
IndianEars
Well-Known Member
My post on Amplifier Feedback & feedforward is here:
Amplifiers: What causes deterioration in stereo imaging, tonal balance and dynamics
I doubt it, arj. All tubes operate at High Voltage & Low current, while 4 & 8 ohm speakers need Low Voltage & High Current (since their impedance is is low... just 4 or 8 ohms) The Output transformer converts the High Voltage & Low Current from the Tube To What the speaker requires.... a loose...
www.hifivision.com
Meh. That quote by itself adds nothing new to the topic. Yes, we know feedback is popular - that is how most people make ”well-engineered” amps: you know, the ones with great measurements and vanishing low distortion.
The above concept is precisely what I am pushing back against -and not just me. There is a reason so many people find flea-powered SETs with zero feedback amazingly musical.
Being a sound engineer or even an amp designer does not give someone a monopoly on deciding what sounds better. It merely means that they have one particular method to achieve their chosen design or recording goals. The goals themselves vary from person to person.
So in short, quoting some guy isnt any kind of definitive rebuttal.
Same here. 3WPC, i have never turned the volume beyond 9-10 and it is the only system with which i have received complaints from neighbors.
square_wave
Well-Known Member
In my amp I can adjust negative feedback gain, I like the sound better when it is kept quite low.
keith_correa
Well-Known Member
Some guy!!!
And it wasn't meant to be a rebuttal, definite or not. A bit touchy aren't we?
Yes. Some GuySome guy!!!
Bruno Putzeys, Co-Founder
Inventor of UcD (Philips), probably still the most widely used class-D amplifier for upmarket audio products. Inventor of Ncore (Hypex), which is generally considered the first class-D amplifier to successfully compete with class-A on audio performance. Developed high performance A/D and D/A converter designs for Grimm and Mola-Mola. Co-founder for Kii Audio. Holds 9 patents and multiple patent disclosures
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