Buffered vs. unbuffered pedal input

[Jule553648]

What are advantages of using buffered inputs on a pedal (like on Tonepad digital reverb).

What is the difference comparing buffered input and unbuffered?

Because on spinsemi site (of the FV-1 chip) it is an application of the chip as guitar amplifier implementation and there is no buffer.

[Derringer]

according to the datasheet for that chip
http://www.spinsemi.com/Products/datasheets/spn1001/FV-1.pdf

the input impedance is between 80K and 120K, which is kind of low

a buffered input remedies that problem. The input impedance of the buffer is high, so it won't load down the incoming signal, no high-end loss, etc. and the output impedance is so low that it will be able to properly drive the low input impedance of the FV-1 chip.

there's more good info on impedance here
http://www.muzique.com/lab/imp.htm

[Hides-His-Eyes]

Does anybody have a block diagram of how a buffered pedal actually works? I've never had it explained to me; I only know the consequences and not the implementation.

[Derringer]

when you say "a buffered pedal" I'm assuming that you mean it has a buffered input and a buffered output?

if that's the case then the diagram would look like this:

signal in ->buffer ->effect ->buffer -> signal out


both buffers would have a high input impedance and a low output impedance.

Check out this article called "The Technology of the Tubescreamer"
http://www.geofex.com/Article_Folders/TStech/tsxtech.htm
Reading about the input and output  buffers should help you a bit.

also, read this one about pedal impedance:
http://www.muzique.com/lab/imp.htm


and this one is good too about buffer design in general:
http://www.muzique.com/lab/buffers.htm

[Hides-His-Eyes]

Where does the switch fit in though?

[Jule553648]

But would it really be an audible difference on 20 watt amp?

What about a bigger amp? How big would be the difference?

Because I am making board on this scheme:

http://www.spinsemi.com/guitar_amp_application.html

[oliphaunt]

Where does the switch fit in though?

In the case you are talking about the buffer is basically a part of the effect circuit and not necessarily on all the time like it is in a Tube Screamer.  

          l_       true bypass      _l
switch l                                    l  output
          l _ buffer-effect-buffer_l

It is up to you whether you need a buffer always on in your system, or just need it to make the chip work in this effect.

I use one buffer at the beginning of my signal chain to compensate for high end loss as the signal travels through 30 feet of cable and 14 pedals, and use truebypass pedals whenever possible can after that.

I just got a Valvulator tube buffer, and I have to say I like it a lot, probably better than any solid state design I have tried.