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? 

[Paul Verticchio]

To me, a bridge rectifier is solid state device consisting of a quartet of diodes connected in series and is used to convert A/C to D/C.

 

If your definition is different, please clarify.

You may also want to look at the schematics of guitars that uses this type of arrangement (like the Fishman Power Bridge or the Graphtech Ghost System). I'm pretty sure that the specific piezo bridge systems are active and have their own "blender" function.

These (piezo + blended magnetic) are pretty standard devices now days so I don't think you have to reinvent the wheel.

 

Best of luck (:

 

[Dave Yelverton]

Would this be of any help?

http://www.fishman.com/files/tune_o_matic_powerbridge_installation_...

[Doug T]

Nope, that's my definition.  If I understand the reason behind powering a blended mag/piezo is that a mag is DC and a mag is AC and by powering it you smoothe the amps and bring impedence down to a level that won't load the mag.  If one were to convert the AC signal of the piezo prior to blend it could be managed entirely passively.  I'll give the powerbridge a closer look, the schematic is interesting.  I have thought of just the blend pot, but I've heard that it tends to be uneven.  Thanks all

[Doug T]

Oops, that's a mag is DC and piezo AC and has very high impedence, which can cause issues.

[Pierre-Antoine Roiron]

Both produce a AC signal (remember they are sound transducers, and sound is alternating pressure level, so is the electric signal representing it ; we're not speaking of electret transducers which are still AC, but DC shifted because they need to be polarized). The only problem is the impedance mismatching that leads to pickups bleeding each through the other, and level mismatching that make passive blending not always efficient. If you want to make a good guitar, use an active blending device. All piezzo makers (almost) offer them, and you can even use a John East device.

[Doug T]

Pierre, thanks for that.  I'm just starting down the path of electronics and the few things about mags I found on the web were describing them as DC.  Maybe I'll just look down the road of active.  I was holding out that there may be a passive method.  I personally like the tone of passive mags, especially hums. 

[Pierre-Antoine Roiron]

You can do it passive, but it's not as good as doing it active. Besides this, pickups will remain passive with a passive tone, as long as you put a passive volume control before the input of the mixing device.

[Paul Verticchio]

If you definition matches mine then "no" that device will appear nowhere in the circuit. It's simply not used in guitar circuitry. It's used in power supply applications (think amps and other A/C to D/C current conversion applications).

 

Good luck with your electronics education & best of luck with your project (:

 

[Donald A. Fortune]

Hi doug- I did a guitar in the configeration that you want to do and I used a rotery blend switch to go from one pickup to the other and it worked out ok.. wire it up on the bench without installing it on the guitar and give it a tap test to se if it works for you before installing it on the guitar.. hope you understand what I am trying to explain to you...Peace, Donald

[Len Biglin]

Doug , I think you are confusing terms here, pickups dont produce DC, batteries do, a pickup puts out ac which corresponds to vibration ( think of a speaker moving back and forth). What you might need is a buffer to reduce the impedence of the piezo signal ( piezo pickups dont sound great unless buffered thru a preamp or into a special acoustic amp), then blend with the bucker.Len

[Russell Vance]

I have used Graphtech Ghost systems and highly recommend them - they have outstanding switching, blend and buffer capabilities through hybrid plug-in switching and combine piezo and passives very well.  They are compact and reliable - I like this setup for its flexibility and it works without any dickin' around trying to match components, pots and pickups etc.

I have attached a photo of just how much you can do with a Ghost system: Tele cavity - three passive pickups and an embedded Ghost pizeo set of saddles - note the blend pot and the "quick" switch (all passive/only active) and the 5 way Schaller selector for standard passives.  Also note the 'plug-in' wiring at the end of the preamp board.   Fitting the battery into this was done during the guitar build (its under the top off to the side of the cavity.  The preamp is also MIDI capable with a piggyback circuit board (not here tho) that provides discrete string to string signals to fire effects and Syth etc. This is not a brag gig, it is what is out there for high level fits on top level instruments and works straight out of the box. The output also automatically switched from full blend mono to individual stereo depending which cable is plugged in.   Nice stuff. Rusty.

[Pierre-Antoine Roiron]

Nice job! It's hard to fit all this mess in a tele pocket, and you've done it well!