Who, How, When do you use your buffers (or not)????

[petemoore]

   I used the Schematic from GGG, a Jfet buffer.
  I didn't 'skip' any perfholes, the whole thing is on a stamp sized perf. The board build itself took about 20 minutes...I managed even to 'not' wire wires that go through access holes until they were fed through them.
  I didn't even pre-test other than to confirm connections...fired right up for the first time in the guitar. I did socket the transistor just because...heat...and it's easy.
  I used a .1uf output cap, 2m2 divider resistors.
  Brightened things right up very nicely  .
  I believe maybe the guitar cable from GC, a 10' cable, loses some high end...

[vanhansen]

I hadn't tried the JFET buffer but I'm sure it's very similar to the op-amp version.  I don't know why I hadn't used one before.

[markr04]

I'm in the midst of another project involving EMGs (wiring the "split-coil" 89, another story), and ran across this. EMG's FAQ says:
Unlike a traditional passive volume/tone system, the low-impedance EMG system lets you turn down the volume with very little effect on the tone, so you won't sound muffled when you back off the volume knob.

So would a low-impedance pickup benefit from a buffer, or does this mean it's not really needed? Although RG's bit explained a lot to me for the first time (nice explanation, RG), I'm just barely above clueless.

[vanhansen]

Good info, Mark.  And you corrected my statement.  I had said they were high impedance.  Oops.

In my experience with active pickups, mostly EMG's, they appeared to have more presence and clarity with long cable runs over traditional passive pickups so I don't think an external buffer would do too much.  I wouldn't think it would hurt any though.

[R.G.]

So would a low-impedance pickup benefit from a buffer, or does this mean it's not really needed?

It all depends on the details. How are you going to get that low-impedance pickup (in a technical sense, not "Well, I'll just go buy it...")?

Impedances in audio obey the rule of ten times: the input impedance being driven should be at least ten times the output impedance driving it.

If you obey that, it pretty much guarantees that you won't have loading and tone loss problems.

Normal guitar pickup impedances vary a lot, because the pickup is inductive. At low frequencies, it's bounded by the DC resistance of the pickup, which is usually in the 5K to 18K range. At high frequencies, it's determined by the frequency and the inductance of the pickup, which may be much larger. This is one reason that we hear a tone loss; it's the treble frequencies where the pickups' impedances are highest, and so that's where loading hits hardest.

So does a low impedance pickup need a buffer? If it's low enough, no. The problem is defining "enough" and then dealing with the side effects of getting to enough.

A pickup with a tenth of the impedance of a normal one would drive ten times as much capacitance as a normal one, or it would drive the same cable with 20db less loss at a given high frequency. However, to get to there with normal technology, you'd have to do one of two things, either wind for 1/10 the pickup inductance or use ten times the magnet strength. Neodymium aside, the practical thing would probably be to wind for 1/10 the inductance. Since inductance varies with the square of the number of turns, the pickup would be the square root of ten times less turns, about  1/3 the windings. That also cuts your signal voltage by 3:1, so you now have a lower impedance signal but with 1/3 the signal level. You'd probably want a booster to get your signal level back. Might as well use a buffer.

If the pickup isn't a factor of five to ten times lower impedance, you haven't gained much in driving the loads.

Details, details, details...

[R.G.]

... but in answering about impedances, I shot right past the comment on EMGs. Active pickups almost certainly already have internal buffers, so no, active pickups should not need buffers. My blater was about low impedance passive ones.

[vanhansen]

Looks like R.G. is getting the "Hammer Syndrome" - that is replying with lots of useful information, definitely worthy of keeping for reference, but not totally answering the question at hand until posting again. 

[R.G.]

... and did I ever tell you about how to make synthetic limestone with portland cement and peatmoss?

[amz-fx]

... and did I ever tell you about how to make synthetic limestone with portland cement and peatmoss???

Isn't that how they built the pyramids?   

-Jack

[R.G.]

Isn't that how they built the pyramids?

Nope. That was caustic soda siloxo-alumina geopolymers (search on "geopolymer" and "Davidovits" to bring it up). 

Geopolymers are an interesting competing technology, by the way, if you haven't read about them. I'm reverse engineering the patents in my spare time to come up with a home-made geopolymer. I -- think-- that household lye, fly ash (check your local readymix plant) and meta-kaolinite (pottery supply) produces a simple one. But I haven't had time to try one out. I have a couple of prepub papers from the conventions of the technical ceramics societies that indicate that the proportions are not as finicky as the patent applications suggest.

And I don't trust a beginner not to eat all the skin off his hands messing about with caustic lye... 

[petemoore]

  "What is that stuff, don't we need gloves?"
  It slowly eats through your hands pants and most anything organic, then you read the label ..."Lye" is listed as active ingredient...then we got *mift [to say the least] at the idiot 'professional painter' who set us up using that stuff to wash a buildings blocks before painting them...my fault...I soon dubbed myself 'safety officer' and it took alot [preferably all day] of idle time [while idiot was away] considering the many issues we had...we lasted only a couple more days after that...lol  because actual work progress had slowed to near halt status...