Question about Feeback Loop

[Barcode80]

I have to say, in all my audio training and such, one question has always bugged me that I was too embarrassed to ask. But what the hell, we all have to learn.

WHAT ON EARTH IS A FEEDBACK LOOP?!?!?!

What is the difference between it and an effects send/return? Is this just terminology for something else I've already heard of?
I just hear/see the term all the time and could not for the life of me figure out what it was.

Okay, newb moment over.... 

[cloudscapes]

in a nutshell, a feedback loop is when part (or all) of the effect's output branches off and is sent right back into its input, all while the output can be heard. sonicaly, things can degenerate and explode pretty quickly. if you can vary the amount that loops with a pot, that makes it even more itneresting!

[Barcode80]

aHA. it all makes sense now. I don't think I have a practical use for that, but I get it now.

[petemoore]

  there's pos feedback
  which makes crazy sounds, is contingent on having just the right amount to not just self oscillate. Amplified signal is fed to an earlier portion of the circuit, where it turns into a 'loop' and is amplified and...feedback looped.
  Without some serious fine tune or other type of control? it gets out of hand real fast.
  Then there's neg feedback [*amps presence controls] which sends a tap from the amp output through a pot to the input, instead of re-inforcing and going crazy, the opposite polarity waveforms cancel each other, an *adjustable amount with pot, or fixed.
  I got a feedbacker circuit working, SD1 clone, with everything set perfect I got neato feedback tone, but getting it to consistantly do that, even set the controls [1meg, 100k too small] to do it once again was very tedious, and...feedback occured whether 1/2 controlling it with playing or not.
  It was hard to say if I hit that button I'd get 1/2 feedback or uncontrollable 110% feedback.
  Here's how I might do it, use a large pot for positive feedback, somewhere in the circuit it looks like you might have enough control on it [maybe like between 2 adjacent BMP stages?] then use a negative feedback control [from output to input] to try taming the + feedback...lol.

[MartyMart]

I've seen it used in a number of circuits, often ( for obvious reasons ) very limited in
frequency and volume.
I have a feedback control on my Matamp valve amp, labelled "attack" which offers some
great tonal/gain changes, fully dimed, the amp breaks up quicker, I guess it's at the preamp
rather than power amp stage, as main vol can still be backed off to same effect

MM.

[pyrop]

The Fuzz Face circuit, possibly the most famous use of a feedback loop in stompbox history.
The red section indicates the feedback loop where the signal is fed back from the emitter
of Q2 through a resistor to the base of Q1.

pyrop

[MartyMart]

The Fuzz Face circuit, possibly the most famous use of a feedback loop in stompbox history.
The red section indicates the feedback loop where the signal is fed back from the emitter
of Q2 through a resistor to the base of Q1.

pyrop

Of course DUH !!
Great example

MM

[Barcode80]

No no, i get how it could be used in circuits. I'm just don't think I would have a use for it externally, like in the feedback loop/A-B box i saw on here the other day. I personally for what I play don't see a use I would need it for as a switchable pedal.

[krachbox]

hi, well for a good example what a feedback does and ifits usefull look here:

http://www.killerrockandroll.com/deathbyaudio/totalsonicannihilation.html

which is of course ridiculously overpriced.

a feedback loop is good for instant and crazy noise and you can use all kinds of pedals (it takes a good deal of experimenting).
imho one of the best simple simple devices for some sonic mayhem.

Janis

[Mark Hammer]

The relationship between feedback and time lends itself to different terms being used for a control that essentially accomplishes the same thing: determining how much of a given ouput signal is "fed back" to some specific return point.

In a flanger or phaser, for instance, returning some portion of the output signal for reprocessing results in frequency emphasis, so the control is often labelled/named "resonance".  In short analog delay situations, the same control may be called "feedback", "echo", "decay", or some other term depicting what it does to the sound.  In longer delay situations, where the delay time is long enough for individual echo repeats to be heard, that same control will often be called "repeat/s".  It is pretty much the same sort of control and process in each case, but because of what happens between the return point and output, different effects are created, so different names are applied.