An onboard buffer for guitars

[R.G.]

Horses for courses.

You can put in a modest amount of gain by inserting some resistors in the complementary feedback pair. However this begins to dilute some of the advantages of the CFP. You can correct for that, probably eating some more battery in the process. And you're still stuck with the voltage ceiling of 6V. You could add a third - or fourth! - coin cell for more volts.

At some point the tinkering gets complex enough to make an opamp a more palatable solution. There are opamps that would do something useful with gain at about 175-200uA per stage, and give you a lot of gain.

However, unless you really need switchable boost inside the guitar, you can put as much gain outside the guitar as you can stand. The buffer has eliminated the problems of control and cable loading, so whether the gain stage is inside the guitar or not depends on other issues, like whether you can stand to have the gain external to the guitar, or must have it coming out of the raw guitar.

A lot of design work comes down to objectives. Change an objective or feature and that ripples back into the design as changes. Some changes, not even huge ones, can ripple all the way back to the start of the design.

[Ben N]

Two more (possibly obvious) questions:
In terms of how to incorporate this buffer, I'm guessing that standard tone controls could be part of one's magic loading, with additional R+C in parallel to taste, to duplicate the loading of the volume pot and cable; then a single volume control, such as on a Tele or Strat would go post-buffer. In that case, should the volume pot should be reduced in value to 25k-100k?
And, in an LP style guitar, do you need to have two buffers?

[Gus]

R.G. why did you use "magic loading" 

There is no magic loading there is the interaction of the guitar/bass R, L and Cs with the cable and the input of the amp or effect after the guitar.   

There is science to the resulting EQ and with software like LT spice etc one can model what they want to happen.

Did you use "magic loading" to start another internet term that will be repeated again and again.

[B Tremblay]

Did you use "magic loading" to start another internet term that will be repeated again and again.

I hope so! Then I can tell my grandchildren that I was there when Sorceror Keen conjured the magic loading! 

Seriously though, maybe RG is paraphrasing Clarke ("any sufficiently advanced technology is indistinguishable from magic") and sparing the less scientific readers from the intricacies of of pickup behavior.

[brett]

Hi
I'd hope that people listen to both Gus AND Brian. Do we need to subscribe to EITHER science OR magic?
I love science, but I also love simplicity and myths.
Magic load? Cool name, I like it personally, but it's smoke and mirrors for sure!
cheers

[gritz]

Magic is just science that's too darn difficult to figue out yet. Or something. 

[R.G.]

In terms of how to incorporate this buffer, I'm guessing that standard tone controls could be part of one's magic loading, with additional R+C in parallel to taste, to duplicate the loading of the volume pot and cable;

All this started with a  complaint/question from a guitar owner that the tone from his guitar suffered with changes from the volume control, and was worst at middle volume control settings. A little thought said that the pickups were loaded most in this position by the volume/tone controls themselves. I opined that a buffer ought to eliminate this, and designed a buffer to meet this need. I believe this would work.

The term "magic loading" cam about when I realized that the loading of the volume and tone control at certain positions was part of the tone the player wanted to preserve, and that it was possible that each player might want a different setting to get just the tone they wanted to preserve. Hence, there was a magic setting that pleased their ears. Magic is real - but it only exists inside the human mind! 

then a single volume control, such as on a Tele or Strat would go post-buffer.

That's one solution.

In that case, should the volume pot should be reduced in value to 25k-100k?

Depends on the pesky humans. Guitar players have this predilection for demanding that their guitars should be defaultable back to the basic magnetic pickup with no electronics. Valid or not, they do. So the right setup for cleanly driving a cable to the amp is a lower volume control. 25K would be good. But then the guitar isn't easily convertable back by flipping a switch.

And, in an LP style guitar, do you need to have two buffers?

R.G. why did you use "magic loading" 
There is no magic loading there is the interaction of the guitar/bass R, L and Cs with the cable and the input of the amp or effect after the guitar.   
There is science to the resulting EQ and with software like LT spice etc one can model what they want to happen.
Did you use "magic loading" to start another internet term that will be repeated again and again.

See above. It was a semi-satirical reference to each guitar player thinking that THEIR pet setting is the magic one.

I hope so! Then I can tell my grandchildren that I was there when Sorceror Keen conjured the magic loading! 

Seriously though, maybe RG is paraphrasing Clarke ("any sufficiently advanced technology is indistinguishable from magic") and sparing the less scientific readers from the intricacies of of pickup behavior.

OK, maybe some of that too. 

I'd hope that people listen to both Gus AND Brian. Do we need to subscribe to EITHER science OR magic?
I love science, but I also love simplicity and myths.
Magic load? Cool name, I like it personally, but it's smoke and mirrors for sure!

Has anyone else been struck by the acronym for smoke and mirrors being S&M?

[JohnBlakeArnold]

Clarification Question:
Are the un-labled pads for a second pick up and do I have them labeled correctly in the graphic?   This is going in a 3 year-old 99$ Dean Evo to drive a 50ft cord with the original cheapo factory pick-ups.  I was also wondering if I could use the stereo jack trick to turn off the battery by unplugging when not in use. Thanks.
 

[PRR]

> un-labled pads for a second pick up

Power Input.

(Hint: those pads go right to a big capacitor. 1uFd will short-out ALL pickup signal.)

[JohnBlakeArnold]

Hi not at my computer right now. I take everything you say as gospel PRR, but is this a jest? A pickup has intermittent signal so could be considered a capacitor functionally.  I may have to instead go with orman's booster cable.  A disappointment because I have parts, but it is big. I saw no capacitor listed.. any help appreciated.

[PRR]

> A pickup has intermittent signal so could be considered a capacitor functionally.

I don't understand that trail of thought.

[Jdansti]

Re stereo jack, connect the board's ground to the ring to use the jack as a switch.

I'll let PRR handle the mystery connections.

[JohnBlakeArnold]

My mistake, I shouldn't have posted. I'll go back to silently lurking and learning. I will use the ghost powered booster cord from Orman.  





I will remove the images after 24 hours. If there was a decent upload process for posting images here rather than using a second URL, I would not have posted the URL in my blog, which no one reads because there is nothing there.  

Actually this schematic is from J. Donald Tillman not Orman, sorry.

[R.G.]

My mistake, I shouldn't have posted. I'll go back to silently lurking and learning.

Don't go getting all passive-aggressive "I'll just sit here and freeze in the dark." on us. 

What Paul was gently trying to tell you is that what you said about "A pickup has intermittent signal so could be considered a capacitor functionally." doesn't make sense electronically, and that there's a gap or mistaken impression in your knowledge that you can get filled in.

A pickup having an intermittent signal does not qualify it for consideration as a capacitor. Capacitors aren't the only things that have intermittent signals. And worse yet, pickups are heavily, heavily inductive; so considering them capacitive leads you way off into the weeds when you start designing around them.

Going back to your original question,

Are the un-labled pads for a second pick up and do I have them labeled correctly in the graphic?

No, those are where the power is provided for the circuits to operate.

This is going in a 3 year-old 99$ Dean Evo to drive a 50ft cord with the original cheapo factory pick-ups.

In that case, put this buffer circuit after everything in the guitar, but before you connect to the input jack itself. It will make a good cable driver.

I was also wondering if I could use the stereo jack trick to turn off the battery by unplugging when not in use.

Yes.

You're doing fine - ask your questions, and appreciate being told the straight stuff in return.

[PRR]

I *agree* that the un-labeled pads may confuse some builders.

Problem is: experienced plumbers kinda "know" what pipes to expect. Here's where water comes into the house, there is where water (and yuk) runs out to sewer, and this third pipe may be gas to heat the water?

So they (we!) over-look labeling ALL the connections.... done it myself too often.

So as a journeyman you want to learn what the master sees. A simple buffer usually needs input, output, and power. You don't have to look for the water-meter to find the input, R.G. did note "from pickup". And the output is over there. But what's this other connection...?

There's a "drawing problem". We have an input and an output, and a power connection that often connects to *many* things between input and output. We may put the input and output left and right. But then the power circuit tends to be in-the-way in the middle. It gets tangled-up. We often try to abstract it into a corner, by using "+6V" arrows here-to-there. That's often confusing also, and I dread those drafting-program schematics which encourage young designers to splatter arrows over all pages of a 6-page schematic (often with mystery designations like "G43").


The Tillman is excellent although in this context the power scheme is broken-up over two units, not like most toyboxes which have it all in one unit. It's not perfectly clean and its uncleanness can be musically useful. It is moderately sensitive to FET selection. The Phantom power option does put the battery over-there where space weight and accessability are no-problem.

The R.G. plan linked here is compact battery and dead-clean. It is not at all parts sensitive (nearly any post-1975 transistors will work).

If you need multiple pickups, the traditional way is a Pickup Switch before the buffer. You could go for a no-knob mixer, or something more elaborate.