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Passive piezos on a P bass

N

Need Gigs

Dec 19, 2013
430
374
Wellington, New Zealand
#1
Hi guys,
I'm considering adding piezo pickups to my fretless P bass. Would it be possible to wire them so that the piezos only amplify the high end and the magnetic pickup (Dimarzio Model P) amplifies only the low end? I'm thinking in terms of a crossover here.
I know that many people recommend a buffer for piezos but I don't think I'll need one, considering I'm not exactly interested in getting huge lows from the piezo ;)
Also, if anyone knows how to deal with the different output levels of piezos vs mags then I'd love to hear from them as well.
Cheers
 
#3
RobbieK said:
I've designed many custom preamps that do exactly what you are asking, but I would doubt that there's any simple solution from off-the-shelf parts. You'll need a buffer for both pickups, both to blend them effectively, and also to get the treble from the piezo.
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+1 this. What you want to do is far easier with active circuitry. The Piezos really need to be buffered so you can get a reliable sound out of them. They are high impedance devices and so will sound quite different with different amps, length of cables, etc.

A crossover would be ideal for what you want. You would need a low pass and high pass circuit, tuned so they crossover at a desired frequency. Whatever that frequency would be depends what part of the frequency range needs to be covered by which pickup. Crossovers can be made with passive components but this will involve volume loss. Active crossovers tend to be more linear and won't cause volume loss in the pass band (unless designed to do so).

In regards to the volume differences, I would point you at a buffer with some gain to make up the volume needed. Alternative would be to use a resistor to attenuate the magnetic pickup's volume down to the level of the peizo.
 
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#5
Because of impedance issues, "passive piezos" is almost an oxymoron. However, on the DB side, you will read about the fDeck preamp. If you want to build from scratch, instead of installing a commercial piezo system like the Graphtech Ghost, Francis publishes his fDeck schematic for D-I-Y'ers. The output can then be sent to a conventional preamp, or straight to either a D-I or a head.
Invalid Link Removed
 
#6
Firstly, all piezo elements are passive. Second, you are definitely going to need buffering. Don't even waste time thinking about a scenario in which you wouldn't. While it might be easy to imagine an application in which the losses associated with unbuffered piezos are not an issue, you are trying to combine piezo elements with magnetic pickups, so buffering is the only way you can mix the two signals without the impedance of the magnetic pickups just shorting out the piezo elements.

I would assume that you wanted a passive crossover system, consisting of capacitors. Would you be open to a simple active circuit? How strong does the separation need to be?
 
#7
line6man said:
Firstly, all piezo elements are passive. Second, you are definitely going to need buffering. Don't even waste time thinking about a scenario in which you wouldn't. While it might be easy to imagine an application in which the losses associated with unbuffered piezos are not an issue, you are trying to combine piezo elements with magnetic pickups, so buffering is the only way you can mix the two signals without the impedance of the magnetic pickups just shorting out the piezo elements.

I would assume that you wanted a passive crossover system, consisting of capacitors. Would you be open to a simple active circuit? How strong does the separation need to be?
Click to expand...
I've got a buffer or two in my signal chain atm (Boss TU-2 and MXR M80). Will these be sufficient?

I'd rather just keep it passive, I'm kinda short of space in the control cavity and changing batteries would be a pain, what with it being a P bass and having to take the pickguard off and whatnot. Cheers anyway though.

I could probably be a bit clearer about this whole thing. What I want is a switch that will give me either just the mag pickup, or the mag and piezo combined. Something like this [Invalid or Expired Link Removed]
I assumed there was some kind of crossover in use to blend the mags and piezo in his guitars. Could be totally wrong though :)

Thanks to everyone that's helped so far!
 
#8
Need Gigs said:
I've got a buffer or two in my signal chain atm (Boss TU-2 and MXR M80). Will these be sufficient?

I'd rather just keep it passive, I'm kinda short of space in the control cavity and changing batteries would be a pain, what with it being a P bass and having to take the pickguard off and whatnot. Cheers anyway though.

I could probably be a bit clearer about this whole thing. What I want is a switch that will give me either just the mag pickup, or the mag and piezo combined. Something like this [Invalid or Expired Link Removed]
I assumed there was some kind of crossover in use to blend the mags and piezo in his guitars. Could be totally wrong though :)

Thanks to everyone that's helped so far!
Click to expand...

The buffering needs to come before the piezo and magnetic signals are mixed. I suppose you could do a passive setup with two outputs going to different places, but then there is the issue of cable capacitance. Also worth thinking about is the fact that piezo elements want to see an input impedance significantly higher than any outboard gear is going to provide. 1M Ohms is standard of most gear, and lower values like 500k are becoming common, as the use of low impedance signals has become commonplace, because it reduces noise. By contrast, a proper piezo buffer should have a 5M to 10M input impedance.

Battery changes should not be an issue. You only need to change a battery once a year or so, if you opt for batteries. Otherwise, there are external power solutions, if you want to go that route.
 
#10
This isn't quite what you are talking about, but Dave Wendler makes his basses with a passive piezo setup along with a magnetic pickup. There is no buffer or power source of any kind. It sounds great actually. I had one of his basses for years and it had a very woody tone, none of that clack that piezos typically yield. You can check out his page with some sound samples at (ElectroCoustic.com)

AFAIK Dave's system is patented, I have never seen anyone else with a passive piezo setuP.

EDIT: I should clarify. Of course, all piezos are passive. My point about the Wendler is you do NOT need a high impedance input for the signal coming out of the bass. Any regular input (DI, amp, whatever) will work fine.
 
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#11
THere are some great sounding passive piezo pickups going around. Especially for double bass. The best sound really woody and mid-rangey, but none sound hi-fi. I'm happy to be shown otherwise, but I'd say any electric bass bridge with piezo saddles or whatever will sound very midrangey without active buffering. I was under the impression that the OP wanted the extended treble from the piezo...

If you are into audio electronics, or you have a friend who is, a circuit to do this is actually very basic. I would think that simple RC filters would be fine for you. Or even just an adjustable HPF on the piezo, as you can roll off the treble of the mag p'up with the original tone pot. You may have to try one of the pickups in either phase to get the right response.
 
#12
I don't know any technical details but there is precedent for completely passive piezo/magnetic instruments in the 60's Supros and Wendler ElectroCoustics. I've owned and played both and both work.

That said I think if you were going for a specific crossover system as described you'd probably get more satisfactory results with an active system. The passive instruments I've played have a distinct (and to my ear pleasing) sound but are not especially versatile and not at all what the OP describes.
 
#13
Cheers, I found the Electrocoustic site yesterday. Used the search function ;)
The sound I'm going for is just a bit more transparent and bitey, with stronger mids and highs. My Model P is probably not ideal for a fretless without a bridge pickup anyway.

Marcus Willett said:
This isn't quite what you are talking about, but Dave Wendler makes his basses with a passive piezo setup along with a magnetic pickup. There is no buffer or power source of any kind. It sounds great actually. I had one of his basses for years and it had a very woody tone, none of that clack that piezos typically yield. You can check out his page with some sound samples at (ElectroCoustic.com)

AFAIK Dave's system is patented, I have never seen anyone else with a passive piezo setuP.

EDIT: I should clarify. Of course, all piezos are passive. My point about the Wendler is you do NOT need a high impedance input for the signal coming out of the bass. Any regular input (DI, amp, whatever) will work fine.
Click to expand...

Marcus, would you recommend Electrocoustic's MagPi system for my situation?
 
#14
Need Gigs said:
The sound I'm going for is just a bit more transparent and bitey, with stronger mids and highs....Marcus, would you recommend Electrocoustic's MagPi system for my situation?
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Based on your stated tone goals, probably not. Dave's system yields a wonderfully rich and thick tone (without being muddy) but I wouldn't describe it as crisp or HIFI. Perhaps an external pre combined might give you what you want, it's tricky.

I was primarily trying to dispel the oft-cited "fact" that a piezo MUST be used with a buffer. True, in most situations (and frankly probably yours) that would give the best results, but Dave's system does sound very good. Is it the sound you are looking for? The sound samples on his website are probably your best source of info.
 
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#15
Marcus Willett said:
Based on your stated tone goals, probably not. Dave's system yields a wonderfully rich and thick tone (without being muddy) but I wouldn't describe it as crisp or HIFI. Perhaps an external pre combined might give you what you want, it's tricky.

I was primarily trying to dispel the oft-cited "fact" that a piezo MUST be used with a buffer. True, in most situations (and frankly probably yours) that would give the best results, but Dave's system does sound very good. Is it the sound you are looking for? The sound samples on his website are probably your best source of info.
Click to expand...

Thanks Marcus.
I actually quite like the sound of the Wendler bass. Maybe the mag pickup from the MagPi system could go in the bridge position, to help get a more focused tone?

I've emailed Peter Malinoski. I'll post bits of his reply here.
 
#16
Okay, here's what Mr Malinoski had to say:
"Yeah Henry, that's a big can of worms. It involves a router and some creative wiring, but I really can't give away 30 years of experience involving this. Here's my advice, ignore what all normal guitar/bass makers say you should do and look at how the cigar box guitar makers do it. You'll figure it out."
I wonder what he means about the cigar box guitars?
 

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