Exploring High impedance to Low impedance Buffer's

Bob Lawrence · From: Beaver Bank, Nova Scotia, Canada

In my post Wanted - A Broken Li'L Izzy: http://bb.steelguitarforum.com/viewtopic.php?t=303320

Craig Baker challenged me to get some books and learn some theory. So here we go Smile

There are a few buffers available (i.e MatchBox , Li'L Izzy, etc. but After reading a few current posts and plenty of older posts I was left with more questions than answers on why we should use a buffer, what kinda of electronic circuit are they, Are they transistor based or op amp based, how to use the buffer , how many buffers are required, how to build a buffer, how to test a buffer, where to get buffer parts, how to repair a buffer etc... I hope to explore as many topics as I can as a learning exercise.

Lets start with :
https://www.arrl.org/shop/ARRL-Handbook-2016-Hardcover-Edition/

and

The Art of Electronics Hardcover â€“ Apr 9 2015
https://www.amazon.ca/Art-Electronics-Paul-Horowitz/dp/0521809266/ref=sr_1_1?ie=UTF8&qid=1467930190&sr=8-1&keywords=the+art+of+electronics

I got this one a few months ago Smile

_________________
Franklin D10, Telonics (E9)True Tone(C6) pickups, Fender Steel King , Evans (FET 500LV), Nashville 400, Quilter MicroBlock 45 amp's, Telonics FP100 volume pedal, PodXT(effects only), Boss RV3(delay & reverb),Steel Guitar Black Box,Bill Lawrence cables, Walker Seat,Peterson Flip Tuner, IVL Steel Rider, IK Multimedia IRig Pro DUO for recording.

John Gould · From: Houston, TX Now in Cleveland TX

There are several threads on Buffers here in the Electronics section of the forum . Should answer several of your questions
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Fender GTX 100 Fender Mustang III Fender Blues Jr. Boss Katana MKII 50
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Brian Evans · From: Nova Scotia, Canada

This is as good a description of how/what/why buffer as I have found. http://www.analogman.com/buffer.htm

They can be any decent quality amplifier with a unity gain (gain of one, basically, what comes in is the same signal level as what goes out) that has a nice high input impedance and a nice low output impedance. Op amp, transistors, etc. The thing with a buffer is you have to design the circuit so that its frequency response is right when it's plugged into a bunch of random stuff like other active pedals, long cheap cords, and so on.

I use a digital reverb pedal. If it's on, it acts as a buffer anyway so I don't need a standalone buffer. Many pedals have a buffer function, but many do not.

John Gould · From: Houston, TX Now in Cleveland TX

http://bb.steelguitarforum.com/viewtopic.php?t=301269
Here's a link to a entire thread about DIY buffers
_________________
A couple of guitars
Fender GTX 100 Fender Mustang III Fender Blues Jr. Boss Katana MKII 50
Justice Pro Lite and Sho Bud Pro II

Jack Stoner · From: Kansas City, MO

MOTU has a small impedance converter. I saw one for about $35. It is passive, not active like the Lil Izzy. It has two outputs, Hi-Z and Lo-Z

http://motu.com/products/guitar/zbox/summary.html

I have no idea how or if this works. I have some MOTU recording gear and saw it on their web site.

Bob Lawrence · From: Beaver Bank, Nova Scotia, Canada

@ John Gould
Re: thread about DIY buffers

Yes thanks. I participated in that one somewhere before

Most threads that I've read deal with preamps and not buffers. While a preamp can have a buffer it wasn't the main goal from what I read.

@ Jack Stoner

re:MOTU has a small impedance converter. I saw one for about $35. It is passive, not active like the Lil Izzy. It has two outputs, Hi-Z and Lo-Z

Thanks, I'll check it out but I would think that with a passive device there would be too much signal loss for such a low level output from the pickup.
_________________
Franklin D10, Telonics (E9)True Tone(C6) pickups, Fender Steel King , Evans (FET 500LV), Nashville 400, Quilter MicroBlock 45 amp's, Telonics FP100 volume pedal, PodXT(effects only), Boss RV3(delay & reverb),Steel Guitar Black Box,Bill Lawrence cables, Walker Seat,Peterson Flip Tuner, IVL Steel Rider, IK Multimedia IRig Pro DUO for recording.

Craig Baker · From: Eatonton, Georgia, USA - R.I.P.

Bob,
I didn't see anyone mention this, but buffer circuits have been around for a long time. It's easy to use a vacuum tube for a buffer.

To do this, you simply take the output of the tube from the cathode, instead of the plate. There are three things to consider in doing this. You sacrifice any gain and may have a very slight loss depending on the design. Next, the output impedance from the cathode is very low while the plate presents a very high output impedance. The other thing that take place is a phase reversal.

In the early days of television, RCA cameras used this to created the special effect of making the picture look like a negative. During the negative scene, you were seeing the video from the phase inverter buffer. It's amazing what can be accomplished by moving electrons around.

Best regards,
Craig Baker

cmbakerelectronics@gmail.com

C.M. Baker Electronics
P.O. Box 3965
Eatonton, GA 31024
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Bob Lawrence · From: Beaver Bank, Nova Scotia, Canada

I guess the theory is that when we pick a string we get the fundamental note and the overtones.(bell like tones)

So just what are overtones (electronically) anyway?

I'll start here
https://en.wikipedia.org/wiki/Overtone

When we use long cables the capacitance in the cable can rob us of some of those overtones:

Next I'll use this link to answer a few basic questions about Capaticance.
https://en.wikipedia.org/wiki/Capacitance

1. So what is capacitance anyway?

Capacitance is the ability of a body to store an electrical charge. A material with a large capacitance holds more electric charge at a given voltage, than one with low capacitance. Any object that can be electrically charged exhibits capacitance, however the concept is particularly important for understanding the operations of the capacitor, one of the three fundamental electronic components (along with resistors and inductors).

2. What is the measurement of Capacitance?

The capacitance of the majority of capacitors used in electronic circuits is generally several orders of magnitude smaller than the farad. The most common subunits of capacitance in use today are the microfarad (ÂµF), nanofarad (nF), picofarad (pF), and, in microcircuits, femtofarad (fF). However, specially made supercapacitors can be much larger (as much as hundreds of farads), and parasitic capacitive elements can be less than a femtofarad.

3. How do we get capacitance from a guitar cable?

In electrical circuits, the term capacitance is usually a shorthand for the mutual capacitance between two adjacent conductors, such as the two plates of a capacitor. However, for an isolated conductor there also exists a property called self-capacitance.

4. How can I measure capacitance ?

I have an older Atlas LCR - Passive Component Analyser
and can measure capacitance by the foot in a guitar cable then add the number of feet to get the total capacitance.

5. HOw can I tell if the overtones are getting through the cable or if they are being robbed by the capacitance of the cable ?

I guess your ear's(assuming your hearing is normal) are the best source . If you can't hear the difference one way or the other it may not matter LOL

However I will try to use a Signal generator and recorded wave files with an Oscilloscope and use the Fourier transform (FFT) function the can show Harmonics in a signal. Hopefully I can observe the input of the cable and the output to compare the differences.

Fourier transform
https://en.wikipedia.org/wiki/Fourier_transform

The Fourier transform decomposes a function of time (a signal) into the frequencies that make it up, in a way similar to how a musical chord can be expressed as the amplitude (or loudness) of its constituent notes. The Fourier transform of a function of time itself is a complex-valued function of frequency, whose absolute value represents the amount of that frequency present in the original function, and whose complex argument is the phase offset of the basic sinusoid in that frequency. The Fourier transform is called the frequency domain representation of the original signal. The term Fourier transform refers to both the frequency domain representation and the mathematical operation that associates the frequency domain representation to a function of time. The Fourier transform is not limited to functions of time, but in order to have a unified language, the domain of the original function is commonly referred to as the time domain. For many functions of practical interest one can define an operation that reverses this: the inverse Fourier transformation, also called Fourier synthesis, of a frequency domain representation combines the contributions of all the different frequencies to recover the original function of time.

What to build? LOL

Lets start with a transistor circuit and try an Op-amp circuit later.

A study of transistor circuits shows that transistors can
be biased 3 different ways. Common Emitter , Common Base and Common Collector. The only one that shows High input impedance and low output is the common collector circuit. It is also known as a buffer or emitter follower

https://en.wikipedia.org/wiki/Common_collector

A few things copied and pasted from the Wiki:

** A small voltage change on the input terminal will be replicated at the output (depending slightly on the transistor's gain and the value of the load resistance; see gain formula below). This circuit is useful because it has a large input impedance, so it will not load down the previous circuit:

** and a small output impedance, so it can drive low-resistance loads:

As you can see it has high input impedance and low output impedance

Now back to the books Smile

_________________
Franklin D10, Telonics (E9)True Tone(C6) pickups, Fender Steel King , Evans (FET 500LV), Nashville 400, Quilter MicroBlock 45 amp's, Telonics FP100 volume pedal, PodXT(effects only), Boss RV3(delay & reverb),Steel Guitar Black Box,Bill Lawrence cables, Walker Seat,Peterson Flip Tuner, IVL Steel Rider, IK Multimedia IRig Pro DUO for recording.

Bob Lawrence · From: Beaver Bank, Nova Scotia, Canada

@ Craig baker

Re: Tube buffer

Yes, thanks! . Allot of us actually use one already. It's called the Steel Guitar Black Box Smile

Tubes all the way.
_________________
Franklin D10, Telonics (E9)True Tone(C6) pickups, Fender Steel King , Evans (FET 500LV), Nashville 400, Quilter MicroBlock 45 amp's, Telonics FP100 volume pedal, PodXT(effects only), Boss RV3(delay & reverb),Steel Guitar Black Box,Bill Lawrence cables, Walker Seat,Peterson Flip Tuner, IVL Steel Rider, IK Multimedia IRig Pro DUO for recording.

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