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3-Way Switch for Magnetic and Piezo
Old 1 week ago
  #1
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3-Way Switch for Magnetic and Piezo

Hi everyone.
I made a guitar out from a little old gasoline tank (sooo sweet) and I put on it a magnetic (Ibanez passive humbucker) and a piezo (disk) pickups. Nothing so fancy...

For the piezo, I built a preamp following this scheme:

https://www.instructables.com/id/Gui...ophone-Preamp/

I've just added an input trim pot to ensure that the hot signal of the piezo doesn't overload the circuit.

I put two volume pots (one for the mag, and one wired at the piezo preamp's output); both go to a 3-way switch (Les Paul style). The out wire of the selector, goes to a tone pot and to the out jack.

Each pickup works really well on its own, but the problem is in the middle position of the switch. In short, in that position, with both volume pots all the way on, I can only listen the piezo... If I gradually turn down the piezo's volume, then the mag appears until I can find a blend. But, again, if I turn the piezo up, it's like it "eats" the humbucker signal and I can't have a good mix of both pickups.

Doing some research, I find out that is normal and I have to do something else than simply put a switch to make the blend mag/piezo working.

Someone can explain me how to do? I wish use the 3-way with my pickups without problems.

Buffer? Diode?

Help me, please.
Old 1 week ago
  #2
I use dual preamps with an active blend/pan circuit. You cannot mix piezo and magnetics together.
Old 1 week ago
  #3
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Quote:
Originally Posted by Jim Williams View Post
I use dual preamps with an active blend/pan circuit. You cannot mix piezo and magnetics together.
Ok, as I was expecting. Can you tell me some model to buy or DIY guide to make one of this dual preamps? I can search obviously, but I was asking if you have your favourite one.
Old 1 week ago
  #4
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Mikhael's Avatar
 

Well I use a 3-way on-off-on switch to ground the output i don't want. The big difference is that I run the piezo output to a full-range amp (PA), while the mag output goes to a guitar amp. This allows me to EQ and effect the piezo output to make it much closer to an actual acoustic sound, since that's what I'm after. You might be after something different, thus this won't work for you.
Old 1 week ago
  #5

The output buffer of the piezo pickup is loading the magnetic pickup. A series 10-20k resistor may help.




-tINY

Old 1 week ago
  #6
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Quote:
Originally Posted by Mikhael View Post
Well I use a 3-way on-off-on switch to ground the output i don't want. The big difference is that I run the piezo output to a full-range amp (PA), while the mag output goes to a guitar amp. This allows me to EQ and effect the piezo output to make it much closer to an actual acoustic sound, since that's what I'm after. You might be after something different, thus this won't work for you.
This make sense, but (maybe I forgot to tell) my piezo preamp is built in the guitar, and my intention is to have one single mono output where I can mix pickups directly from the guitar.


Quote:
Originally Posted by tINY View Post

The output buffer of the piezo pickup is loading the magnetic pickup. A series 10-20k resistor may help.
In series with the magnetic, I suppose. I can try this before rebuild a new preamp with a built in blend.

Do you think that a diode can do the same work? Or is the current coming out from the humbucker too low to open it?
Old 1 week ago
  #7
Quote:
Originally Posted by MatteoCT View Post
Ok, as I was expecting. Can you tell me some model to buy or DIY guide to make one of this dual preamps? I can search obviously, but I was asking if you have your favourite one.
I've built my own since 1972. Each has a gain trimpot to equalize the levels. Input impedance is 5 meg ohms. One version is a 3 band fixed EQ, the other is a two band sweep EQ. Send me an email for more info.
Old 1 week ago
  #8
Gear Guru
 
Brent Hahn's Avatar
 

For something similar with an acoustic guitar, would it be possible to wire a magnetic and a piezo to the tip and ring of a TRS jack mounted in the guitar (as opposed to the usual TS) and split them at the other end of the cable? There would probably be a bit of crosstalk, but so what.
Old 1 week ago
  #9
Quote:
Originally Posted by MatteoCT View Post
In series with the magnetic, I suppose. I can try this before rebuild a new preamp with a built in blend.

Do you think that a diode can do the same work? Or is the current coming out from the humbucker too low to open it?

No. Between the output of the pre-amp and the 3-way switch. It's the same concept as a "passive mixer" circuit.

Diodes are bad for AC signals unless you're making a dirt box.



-tINY

Old 1 week ago
  #10
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Mikhael's Avatar
 

Quote:
Originally Posted by MatteoCT View Post
This make sense, but (maybe I forgot to tell) my piezo preamp is built in the guitar, and my intention is to have one single mono output where I can mix pickups directly from the guitar.
I kind of assumed that. All mine have preamps in the guitar, but I have a Fishman Aura pedal I use to add "wood" to the sound.

I don't think the diode would work; wouldn't that clip the sound when it fell below the threshold?

I think the resistor is to try and isolate the preamp output from the pickup coil. I'd put it on the preamp output. Honestly, I'd guess that a preamp that takes both the piezo and the mag would be best, as it would electronically isolate both. I know the Graphtech Ghost preamp has that capability. Personally, I didn't use that method because I wanted the mags to go out without any modifications at all.
Old 1 week ago
  #11
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Quote:
Originally Posted by Brent Hahn View Post
For something similar with an acoustic guitar, would it be possible to wire a magnetic and a piezo to the tip and ring of a TRS jack mounted in the guitar (as opposed to the usual TS) and split them at the other end of the cable? There would probably be a bit of crosstalk, but so what.
As I said, I need to route both pickups to the out jack, because I want a mix of them "on the go" from the single mono out of the guitar. Using a TRS is simpler of course, but isn't what I'm trying to achieve.


Quote:
Originally Posted by tINY View Post

No. Between the output of the pre-amp and the 3-way switch. It's the same concept as a "passive mixer" circuit.

Diodes are bad for AC signals unless you're making a dirt box.
Oh, ok. Thanks a lot, I will try as soon as I can.


Quote:
Originally Posted by Mikhael View Post
I kind of assumed that. All mine have preamps in the guitar, but I have a Fishman Aura pedal I use to add "wood" to the sound.

I don't think the diode would work; wouldn't that clip the sound when it fell below the threshold?

I think the resistor is to try and isolate the preamp output from the pickup coil. I'd put it on the preamp output. Honestly, I'd guess that a preamp that takes both the piezo and the mag would be best, as it would electronically isolate both. I know the Graphtech Ghost preamp has that capability. Personally, I didn't use that method because I wanted the mags to go out without any modifications at all.
Ok so the diode is definitively out from the possible solutions, as tINY also said.

I will try to put this resistor on the preamp out and listen what happen. In the meantime, I will look for some double preamp circuit.

I don't really care if the mag goes into a pre, because this tank-made guitar doesn't need to be this... refined and perfect. All the theories about "sound purity" fell down...


Quote:
Originally Posted by Jim Williams View Post
I've built my own since 1972. Each has a gain trimpot to equalize the levels. Input impedance is 5 meg ohms. One version is a 3 band fixed EQ, the other is a two band sweep EQ. Send me an email for more info.
I'll do for sure! Thanks!




Thanks a lot to everyone for the precious suggestions!
Old 6 days ago
  #12
Gear Guru
 
Brent Hahn's Avatar
 

Quote:
Originally Posted by MatteoCT View Post
As I said, I need to route both pickups to the out jack, because I want a mix of them "on the go" from the single mono out of the guitar. Using a TRS is simpler of course, but isn't what I'm trying to achieve.
Oh, sorry. I led you to believe that I was asking you specifically, and it was about a solution to your specific problem. Neither was the case, but I can see why you may have thought so. Again, my apologies.
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