Buffer Types

[upspoon12]

Hey guys,


Im starting to build some custom looper pedals, and the question of buffers comes up frequently. What are the charactoristics of a jfet buffer vs an ic buffer and how does placement and the front or back or both of the looper matter? i know at the front it helps to drive the signal and prevent loss. The name of my game is preserving as much of the natural sound of the guitar as possible. I intend to make the buffer(s) switchable (using a toggle ) incase one were to put a buffered pedal in front of the looper (which will be 5 channels)
also - could it be beneficial to have one at the front and back of the looper line?

Will welcome all thoughts/suggestions etc!

Thanks guys!

[Mark Hammer]

Buffers at the front and back of loopers would serve different sorts of functions, and those functions would also depend on the circumstance the player is in.

As Pete Cornish has noted, the frequent use of "true bypass" pedals has increased the likelihood that a guitar signal can end up travelling through a rather lengthy sequence of short and long patch cables without any buffering along the way to combat what the cable does.  So, a buffer at the input of a multi-station looper means you can pretty much stick whatever you want after it and the signal will always be a good impedance match to the input of the first thing it encounters, and successfully reach that pedal, intact.

Although the vast majority of pedals will have an output impedance low enough to suit what comes after them, in some instances there also needs to be higher current drive.  In those instances, a performer is not dealing with a 20ft cable to their amp, but something on the order of 150ft or more, perhaps to a board at the mixer desk out in the festival audience.  Yes, the last pedal has a low output impedance, but the output simply does not have enough "oomph" to survive that distance.

Something like the AMZ Super Buffer ( http://www.muzique.com/lab/superbuff.htm ) is intended to address that sort of situation, by paralleling multiple op-amps to deliver an output with more current drive.  Will all loop-selectors need this?  Nah.  I would imagine for the vast majority of players, simply having an always-on buffer so one can use whatever number of TB pedals you want, is going to be enough. 

[upspoon12]

This is good information, the long cable runs i know definitely require one, and using many pedals which may not have buffers will require one.

My next question would then be, if you have many buffers together will this degrade the sound? will they impede each other etc?
I would like to put one at the front of the looper and back of the looper (both toggle-able) to include any situation the player may encounter.
so if said player had both those on, and maybe other buffered pedals as well, would it be adversely effecting the tone? (obvoously less is more take s a roll )


I did infact check outthe amz buffers. I use a couple of amz boost pedals on my board as well i love those things. I wonder if a fet buffer is better at front end or back or both as opposed to an op amp circuit?

[tca]

...by paralleling multiple op-amps to deliver an output with more current drive. 

Only one  mosfet working in common drain will drive anything, no need for *multiple op-amps*.

[amptramp]

A single JFET in a Tillman amp gives you some gain and an output impedance equal to the drain resistor, usually 6.8K.

If you want a really low output impedance and can use dual supplies, this has always been a nice buffer that would need no coupling capacitors, so it is flat down to DC.  The frequency response begins to roll off in the MHz, so it is good for audio and has a 400 K input impedance:

http://phonoclone.com/pdf/lh0002.pdf

[Mark Hammer]

...by paralleling multiple op-amps to deliver an output with more current drive. 

Only one  mosfet working in common drain will drive anything, no need for *multiple op-amps*.

Good point.  Many ways to achieve the same objective.

My next question would then be, if you have many buffers together will this degrade the sound? will they impede each other etc?

They shouldn't.  Since they are unity gain, it's also not like they will contribute any noise.  But I can't see needing more than one on the input and one on the output...UNLESS, for instance, a customer runs a 25ft-er from guitar to the pedalboard, a pair of 25footers from pedalboard to the amp's effect loop, and another 25 footer back to the amp's input jack.  Even there, one would think the amp anticipates cable runs to/from outboard effects patched into the loop.

[Gus]

Your building custom looper petals and you want free advise for the buffer to use?
A google etc search or look up textbook circuit and read about why you pick one or another
Did you do a search for "buffer" here lots of posts.

Often it is about what you will be connected to and the interaction with the guitar or bass or...