Author Topic: "The Sound of Feedback"  (Read 4992 times)

Gen. Dreedle

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"The Sound of Feedback"
« on: October 12, 2010, 08:45:02 AM »
Not to be confused with the sound of silence.

Anyway................

Over at The Pub, we have a real rip-snorter going. One of our buddies, said the following:

Quote
If you like the sound of more feedback, then I guess so.

(He may not like us referring to him as "one of our buddies". Could harm his business. Not our intention.)

To which, some Pommie bastard (ok, he may not be a bastard.............I have no idea. Just little use for Pommies, who think they know electronics. Those people seem to have not made much progress since the Steam Age.)

Quote
Only according to you does feedback have a sound.

(OK, the part about them being stuck in the Steam Age is really the opinion of a former boss, of Hun descent. I just thought adding it in would unnecessarily inflame some folks, so I do my best to live down to their expectations. Back to the story..............)

Anyway, the sound of feedback.

Back in the 90s, when I owned and ran a very obscure audio company, we built amps that had no overall feedback, but used an output stage that had its own little feedback loop. It was the stage that Pass and Rowland were also using, at that time. Yep, a complimentary feedback pair. Worked ok. Slight tendency to oscillate, at 2-5 MHz. But, other than that, it seemed to work ok.

It just needed a stinking bias spreader. And I got sick of bias spreaders.

So, one day....................

I took the exact same parts, had to add a few (Like some LEDs, to make a reference for a current source. Yes, could have done it without those. But, just pretend it used the exact same identical parts.), to get it to operate in the manner we deemed correct, i.e., no bias spreader.

Yeah, made a diamond follower. Same transistors, just rearranged from CFP to diamond buffer.

Hooked it up, without measuring first.

"What the hell did you do? Everything sounds more natural now."

I think we may have measured it, at one time. Not sure though. Not sure what it would have told us, if we did. Anyway, we got hold of as many amp owners as we could, and talked them into "upgrading" their existing POC (that we made), for a "mo' bettah" sounding POC.

No one ever asked to have their POC reverted to its original state.

From that, we concluded that feedback does have a sound.

I guess you could say it is like jitter:

"I don't know what it sounds like, but I know when I don't hear it."

There is your answer. Go ahead, tell me I am wrong. I really don't care.

Because I hate you guys. I hate you guys, so very, very much.

Yours,
Gen. Cartman Lee.

(Yes, I know my signature makes that redundant. But it is because I really do hate you guys.)

And I notice that someone broke the New Year's Resolution. Nice to know we are all human.
"Major Danby, sir."
"Danby. D-A-N-B-Y."
"Take him out and shoot him."
"Sir?"
"I said take him out and shoot him. Can't you hear?"

MystereoN

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Re: "The Sound of Feedback"
« Reply #1 on: October 12, 2010, 11:32:07 AM »
agree with that buddy. The sound of feedback....more like lack of relaxed sound  ;D

I'm just imaging human body instead of electronic circuit .....then feeding output back to input...

Sound of feedback = taste of feedback?  :-[
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seagreen

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Re: "The Sound of Feedback"
« Reply #2 on: October 12, 2010, 11:50:05 AM »
I was weak.  Very weak.

And as it turns out, stupid.  Very stupid.

Why even try to inject some thoughts into a subject when everybody's mind is made up?  Nobody even attempts to consider what you've presented, whether they agree or violently disagree.  Even if you cite that holy grail of information: Papers from professional journals that are refereed prior to publication.

I am *sooo* ashamed...
No double blind testing was used in the making of this post.

Gen. Dreedle

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Re: "The Sound of Feedback"
« Reply #3 on: October 13, 2010, 08:31:35 AM »
The only people who should be ashamed are the naysayers, who think that if it measures good that it has to sound good. And are not willing to accept any alternative.

Many years ago, I had dinner with some economist, named Bill Conrad. Some may have heard of some company called Conrad-Johnson.

Bill is a smart guy, but has no formal education in electronics. Which, one could conclude, he was never indoctrinated in the way things work. Not knowing any better, he is free to try things that fly in the face on conventional wisdom.

One thing he found was that for each product they built, there was a certain point at which just the right amount of OLG was were the (pre-)amp sounded right. Too much, or too little, it didn't sound good. They had to listen to each and every design, for that point where everything seemed to just fall into place. Which also means that he was tweaking the amount of global feedback.

Of course, this is just anecdotal experience, based on their personal preferences.

Wish my anecdotal experiences and personal preferences sold that much gear, and made me tons of money.

One could argue that their designs, especially amps, needed some feedback to control output z and distortion. Something SS weenies, like "our buddy", mentioned in the first post, are able to accomplish, without global feedback.

I still hate those guys, but perhaps even more, today.
"Major Danby, sir."
"Danby. D-A-N-B-Y."
"Take him out and shoot him."
"Sir?"
"I said take him out and shoot him. Can't you hear?"

seagreen

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Re: "The Sound of Feedback"
« Reply #4 on: October 13, 2010, 11:06:51 AM »
My attitude now is that I just don't care what they think.  The only time they bother me is when I let them.

I suspect I have more fun with the hobby than they do (it is a hobby whether you are a hobbyist or selling to hobbyists).  But perhaps not.

'N I don't care.
I just don't care.

One of the things I've found in Cordell's book is that the no negative feedback amplifiers he describes are pretty much similar in performance to the ones that use feedback, at least by the measurements.  With loop feedback you can be more sloppy about the power supplies, since the feedback takes care of power supply detritus, so it says.  But there's also a lot of other criteria that you have to adhere closely to make amplifiers with lots of feedback work.  So, to me anyway, it's a tradeoff at least as far as measured results go.  The big emphasis in the end seems to be almost entirely economic.  High feedback amplifiers are supposed to be more forgiving and therefore less expensive to manufacture.  Hmmm...

One OT note: A section that sprung out at me was about common mode distortion and how feedback doesn't have any effect on it.  Isn't that a problem?  Aren't most power amplifiers with lots of feedback based around the balanced bridge concept of using perfectly matched terminations at the two nominal amplifier inputs to cancel common mode effects?  How do you control that with different source impedances?  Or even the capacitance of the interconnect cable if the preamp doesn't have present uber-low output impedance?  Or how about the volume control in a preamp at the non-inverting input?  Huh?  Huh?  Anybody?  Bueller?  That doesn't even have anything to do with AM-PM conversion, differential inputs acting as phase detectors, or any of that designated voodoo.

No double blind testing was used in the making of this post.

Gen. Dreedle

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Re: "The Sound of Feedback"
« Reply #5 on: October 13, 2010, 12:29:33 PM »
Oh, they have fun. If by fun, you mean looking down their noses at us.

As for real fun, I don't think they ever have any. Spending $600 on some rotted grape juice is not my idea of fun.

A $2 bottle of cheap rotted grape juice..................now I can see where some might have fun with that. (Well, discounting how one feels the next morning.) A lot of us "got lucky", with that $2 bottle, and some hippie chick.

Speaking of hippie chicks..................

Where is Bob Crum when you really need him?

Oh, well, the inevitable gets us all. Eventually.

The only thing I noticed about Bob's no-feedback ideas is that they borrow heavily from high-bandwidth input amps, for 'scopes. Somehow, I don't think "our buddy" (mentioned above) has anything that elaborate.

His credo must be "Well, if it doesn't have feedback, it damn well better have complexity! Otherwise, it can't work.'
"Major Danby, sir."
"Danby. D-A-N-B-Y."
"Take him out and shoot him."
"Sir?"
"I said take him out and shoot him. Can't you hear?"

seagreen

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Re: "The Sound of Feedback"
« Reply #6 on: October 13, 2010, 12:55:30 PM »
Complexity is its own reward.

On the loop feedback free amplifier at the top of this thread, I've just yesterday read that there has been no adequate double blind testing ever accepted that shows any advantage at all to going without feedback.  Of course, even if you accept that as The Absolute, ahh, Truth, the flip side is that there has been no accepted testing that has shown a disadvantage, either.  So, where's the problem?
No double blind testing was used in the making of this post.

seagreen

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Re: "The Sound of Feedback"
« Reply #7 on: October 14, 2010, 07:16:54 AM »
So, since defined simulations and blind testing are what really drives (some) people, we need to get back on the DBT of jelly filled donuts. 

We ruled out the guinea pig from the cannon testing, and it's a good thing we did.  It seems someone has done a detailed simulation of something very similar already!

http://www.wired.com/wiredscience/2010/10/physics-of-angry-birds/
No double blind testing was used in the making of this post.

MystereoN

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Re: "The Sound of Feedback"
« Reply #8 on: October 15, 2010, 01:37:05 AM »
we should spare guinea pigs and test cannon with canadian barking dog, who is barking up the wrong tree. That WUSSY with wife's words in signature should be shoot to the Mars where he could claim his posts in the name of Mars.
Never argue with a fool,
they will drag you down to their level,
then beat you with their experience!!!

zinsula

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Re: "The Sound of Feedback"
« Reply #9 on: October 15, 2010, 12:31:07 PM »
And that "wussy" is even a mod there.

Is there a DBT for choosing mods? Does that relate to the ballistic trajectory? And how do the donuts have any effect?

I'm confused.
Please continue with the sound of feedback. So I can contribute.
http://www.youtube.com/watch?v=ojyA0I6EnBw&feature=related

Before the general asks -- no, I'm NOT from sweden!

Gen. Dreedle

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Re: "The Sound of Feedback"
« Reply #10 on: October 16, 2010, 12:23:31 PM »
There must be something in the water, up there in Canada. I like the idea of launching the barking dog, but it may not fit, into the cannon. Think it best we stick to launching guinea pigs.

Maybe we need to investigate a DIY rocket, capable of sending the barking dog, and several of its companions, to Mars. They can claim it as a DBT Planet.
"Major Danby, sir."
"Danby. D-A-N-B-Y."
"Take him out and shoot him."
"Sir?"
"I said take him out and shoot him. Can't you hear?"

Gen. Dreedle

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Re: "The Sound of Feedback"
« Reply #11 on: October 16, 2010, 12:42:53 PM »
This is a bit o/t, but it shows we are not alone, in our fight against close-minded know-it-alls.

Over here, we have our biennial food-fight, aka the "midterm elections" about to happen. Each side is doing its best, to whip up their supporters, to vote out the other guy. One side only has to point to what the other guys are doing, and most folks are about ready to grab their guns.

The other side..............

They have to resort to specious remarks, like the other side has powerful business allies, who are using foreign money, to help drive the commies out of office. Without proof they are using foreign money.

Normally, the lapdog lamestream media, would join in, and gang up on the evil capitalists. But, the media, sensing their buddies are going to lose (and lose badly), are trying to play both sides of the fence. Of course, no one believes their sincerity, but it damn sure makes for good political theater. And, that is pretty much what the feedback debate is.

IOW, right up our alley! In terms of entertainment potential.

So, some propagandist gets on the idiot box, and tries to sell this idea of foreign money, to a normally sympathetic dupe. But, he ain't buyin' it!

"Do you have any proof? What little they may be, seems to be 'peanuts'."

To which, he replies....................thinking he has him on the run.................

"Well, do you have any proof that is only peanuts?"

So, to summarize: you first make a false claim. When asked if you have proof, you reply that you don't have proof that it is a false claim.

"Why didn't you just say it is like that old 'when did you stop beating your wife' story?"

Because, this way, it is funnier. And wastes more BW.
"Major Danby, sir."
"Danby. D-A-N-B-Y."
"Take him out and shoot him."
"Sir?"
"I said take him out and shoot him. Can't you hear?"

MystereoN

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Re: "The Sound of Feedback"
« Reply #12 on: October 18, 2010, 09:47:01 AM »
Trade secret, how to "improve virtually every known performance characteristic of audio power amplifier".....except sound  ;)
Never argue with a fool,
they will drag you down to their level,
then beat you with their experience!!!

Gen. Dreedle

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Re: "The Sound of Feedback"
« Reply #13 on: October 18, 2010, 12:03:56 PM »
"Unwarranted complexity".

Maybe if you use some of the ideas, in Bob Cordell's book.

Hmm, taking the same ol', same ol' amp, and adding a resistor, to each stage, to utilize local feedback is "unwarranted complexity"? Give me a break.

"What...............arm, leg, or neck?"

None of those, actually.
"Major Danby, sir."
"Danby. D-A-N-B-Y."
"Take him out and shoot him."
"Sir?"
"I said take him out and shoot him. Can't you hear?"

MystereoN

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Re: "The Sound of Feedback"
« Reply #14 on: October 18, 2010, 04:40:31 PM »
"Unwarranted complexity" originated from HERE  ;D

Much better cookbooks can be found there. THIS for example  8)

Some links will work and the others won't.
Never argue with a fool,
they will drag you down to their level,
then beat you with their experience!!!