Buffering Buffoon

[zpyder]

Sometimes for an object or an idea there's a term that is simultaneously informative and elusive.  They can sometimes lead to very silly questions, like:

What is the purpose of a buffer?  I've seen that boosters (simple amps) can be used as buffers... but, why?  What for?  What do you get from a "buffer" and how is it different from a simple amp?


thanks
zpyder

[Pushtone]

Check out the short bit of text "What do buffers do" at the bottom of this page
http://www.generalguitargadgets.com/index.php?option=content&task=view&id=69&Itemid=100
This sums up why I needed a buffer in my signal chain.

Then there this one...
http://www.petecornish.co.uk/case_against_true_bypass.html

And this one... FAQ #3 about half way down page
http://www.customaudioelectronics.com/frequently_asked_questions.htm

Like all things in life, you need to find a balance between buffered and true bypass.

[Pushtone]

Another name for a buffer:

Unity Gain Pre-amp

[phaeton]

The buffering part is understandable, but why don't they make "true bypass" Bayer?

[Thomas P.]

in most cases (maybe all) they're use to match certain impedances and they are no different from a simple amp if you mean basic (non-)inv amplifier as they all alter the output impedance in respect to the input. sometimes we don't want any gain added so we use a unity gain amplifier aka buffer (as one of the fellow answerers already said).the need is simple: low ohmic source but the need of a long shielded cable, etc.

[amz-fx]

Then there this one...
http://www.petecornish.co.uk/case_against_true_bypass.html

I did actual testing on true bypass and posted my results here:   http://www.muzique.com/lab/truebypass.htm

Basic buffers:  http://www.muzique.com/lab/buffers.htm

AMZ Super Buffer:  http://www.muzique.com/lab/superbuff.htm

regards, Jack

[zpyder]

thanks!!


zpyder

[Satch12879]

Buffers do NOT match impedances; they bridge impedances.  If you were to match the input impedance of one device to the output of the other - meaning making input equal output - you'd get a 50% reduction in level due to voltage divider action.

At their most basic, a buffer presents a sufficiently high impedance load to whatever source you choose to drive it with.  The rule of thumb is that "high" is approximately 10x larger and that is the minimum.  And it's done to minimize or eliminate these kind of loading effects.

While simple buffers do also offer low(er) output impedances, it does NOT mean they have the capability to drive every load, or the ability to deliver the appropriate current that the load requires.  Single transistor buffers are a prime example.

Repeat: low output impedance does NOT mean high drive capability.

Further, "unity gain" is a squirrely concept, depending on whether you are talking balanced or unbalanced lines.

Please see these two Rane Application Notes, possibly the two MOST informative technical documents on audio electronics design I've come across:

Unity Gain and Impedance Matching: Strange Bedfellows

Practical Line Driving Current Requirements

[R.G.]

The purpose of a buffer is to make impedance differences NOT matter.

[bluesdevil]

The purpose of a buffer is to make impedance differences NOT matter.

Thank you!!