Use of rectifiers

[Doug T]

I have recently been considering a build with a hum neck and piezo bridge.  My concern is that the piezo will overdrive the hum and essentially make for a hell of a time blending the signals passively.  Could one use a bridge rectifier between the piezo and blend to smooth the signal and make the signals compatible? 

[Doug T]

Russell, that does look great.  I'm going to do a acoustic/electric slimbody with traditional bridge, so I'll need something more along the fishman direction.  Thanks again for the info, I'm still waiting for the books to come in on Interlibrary Loan, but these brief explanations are much clearer than the longwinded stuff I was finding. 

[Rob Mercure]

Doug,

 

Others have done such a good job of providing assistance I've hesititated to chirp in - but on considerations perhaps a few tidbits I could provide might help. You're probably aware that the way we hear - "anything," music, noise, politicians - is by sound waves impacting on the ear drum that are first compressed and then rarefied thus creating a difference - this is the equivalent of alternating current (AC) as it swings from a zero point in one direction (positive by convention), returns to 0, and the swings negative.  Direct current is quivalent to the static air pressure - it's 14 psi (SAE sea level) or here at 2,600' about 12.3psi but my ears can only hear the variation - not the static pressure.

 

Someone has already noted that all pickups produce AC and to elaborate, all musical instruments produce an alternating air pulse which when applied to a microphone is AC.  But many sounds aren't of a high enough varying air pressure so they need to be amplified and, for all the purposes that you'll ever probably encounter, all amplifiers use DC as a power source - whether they be called amplifier, preamplifier, buffer, equalizer, etc., they're all amplifiers and most included in an instrument use solid state devices of some sorts (transistors, FETS, ICs MOSFETs, etc.,) so the DC voltages involved aren't high and usually multiples of 1.5 VDC or 9 VDC for obvious reason (yeah, there was a period of low voltage tubes before silicon dominance but if you encounter one in a guitar some eccentric crank like me built it in - not factory work).

 

Lastly, as long as P/Us were electromagnetic and produced a signal by vibrating a bit of ferrous metal in a magnetic field the signal strength had enough current to make P/U swapping/mixing fairly simple.  As a working analog you can compare voltage and current to water pressure and water - related items but not the same.  Piezos can be thought of as having really high pressure but no water associated (very high impedance) so when you hook them across a magnetic pickup all the pressure just dissipates away.  So to bring down the "pressure" and up the "water" (voltage/current) a small amplifier called a "buffer"  - usually with a power gain of 1 or less (doesn't "amplify" as much as simply "match") - is used and now you can blend the piezo and emP/U signals together.

 

Hopefully this will provide some framework for whatever materials you're acquiring.  There used to be lots of good info at Steve Ahola's "Blue Guitar" site on this as well as links to other sites.  Perhaps someone here could provide a good "modern" reference text as most of the ones I'm aware of were written in the 1980-90s and contain lots and lots of incorrect information about electronics - Kevin O'Conner with his London Power line is generally good on amps but still draws an occasional strange assumption, has a "very Canadian" <grin> defensiveness, but mostly are just expensive especially if guitar internals are your primary interest.

 

Rob

[Doug T]

Rob,

That explanation of sound as AC is great and now is obvious to me, and the analogy to water really brings it together.  I'm really an acoustic builder but have been told by all the serious players around my neck of the woods that acoustics "Just ain't used" and you need to have at least a slim acoustic with at least one humbucker.  Glad it's humbuckers because I prefer their tone to single coils.  And besides, you can tap them and the player can have a single coil if they want.

again, thanks all

Doug