Replies to This Discussion

Permalink Reply by David L. on February 24, 2010 at 6:56am

Hi Fergus,

I always wire mine in parallel because if one breaks the other(s) will still work. Also in series the impedance increases with each additional piezo (and as thay are high impedance to begin with most articles state this is not a good idea - not sure what affect this has on your amp in reality, I guess it must stress it) by wiring in parallel the impedence reduces. I found one book with a bit in it here http://books.google.co.uk/books?id=ynxQQJfcf3oC&pg=PA53&lpg...
page 53 if it opens at the beginning rather than the desired page.
I am afraid my electronics theory is too weak to explain better.

Regards,
David

Permalink Reply by Mama Mojo on February 24, 2010 at 9:24am

I think that the output is greater in the ones where I've used two.... the single ones seems weak to me.... But I also use pots and wire up the volume at the very least and that probably makes a difference....

Permalink Reply by Fergus Morris on February 24, 2010 at 9:37am

Thanks, those are both handy bits of information, and useful link, David. The build I had in mind when I asked this already has 2 magnetic pickups, but i want to make it a piezo hybrid, so I think I will wire two piezos in parallel with an on/off switch to the jack, thanks for both of your advice.

Permalink Reply by Eli Spiegelman on February 26, 2010 at 5:28am

If you don't mind, can you explain why you'd want both piezo and magnetic pick-ups?

Thanks,

Eli

Fergus Morris said:

Thanks, those are both handy bits of information, and useful link, David. The build I had in mind when I asked this already has 2 magnetic pickups, but i want to make it a piezo hybrid, so I think I will wire two piezos in parallel with an on/off switch to the jack, thanks for both of your advice.

Permalink Reply by Fergus Morris on February 26, 2010 at 5:47am

So I can get more tones - i just really like messing around with the controls and getting different sounds. I did it on a bass I made and mixing them or having piezos on their own allows me to get some fairly unique tones

E. BigOldMan said:

If you don't mind, can you explain why you'd want both piezo and magnetic pick-ups?
Thanks,
Eli

Permalink Reply by Larry McInnes on April 15, 2010 at 3:29am

I have a Parker electric guitar that has both humbuckers and a piezo pup. The switch allows you to turn on one or the other of the pups or both. Makes for some nice tones.

Permalink Reply by Murray on May 23, 2010 at 9:27am

(Un-)solicited electronics rambling...

Evidently putting piezos in series must work, based on what others have said, but not having tried it, based on my initially frustrating experience making an overdrive 'unstomp' box for a violin with naive assumptions about piezo impedance, I will never try series piezos...I had some really bad hum, noise and frequency response issues with the very highest impedance ones (75 mm length of piezo polymer coax), and can't believe how agreeable a large polymer ribbon (~3/4" x 3") piezo has been with everything I plug it into....

A magnetic pickup is (simplified), a coil of wire or inductor. An inductor's electrical property 'L' (inductance) is essentially a constant and independent of frequency. It's impedance (XL=2 x Pi x f x L) however is proportional to (increases) with frequency, so the combination of a magnetic pickup's impedance and a conventional amplifier's input impedance has a general characteristic of a low-pass filter. If you put two identical magnetic pickups in series the combined impedance at a particular frequency doubles in a way that the high frequency rolloff point is cut in half...it may sound less bright, depending on the amp impedance. Inductance and impedance of inductors, and (magnetic pickups) in parallel reduce in a manner similar to resistors in parallel...it is reduced. Paralleled magnetic pickups generally sound brighter. Cable length complicates the issue, but that's a summary.

A piezoelectric sensor (and an electret for that matter) is (simplified), a capacitor. A capacitor's electrical property called capacitance is essentially a constant and independent of frequency but it's impedance is inversely proportional to frequency (decreases with increasing frequency). Because of that inverse dependence of frequency, a capacitor's impedance reduces with increasing frequency Capacitors in parallel ADD in capacitance,the way inductors in series add.
Xc = 1/(2 x Pi x f x C). (Pi, of course being that weird little Greek letter that looks like a Spanish tilda on crutches, that you needed in school to figure out area and circumference of circles before you decided being a professional musician sounded better than geometry.)

When you put capacitors in series their combined capacitance is reduced, and there are not a lot of times it's done. The worst effect this has is that a piezo pickup and the input impedance of an amplifier behave as a high-pass filter. If your piezo impedance is too high for your amp impedance, you will have reduced or poor low frequency response...this is used to advantage with string instruments like bass, cello, etc, in a controlled way, so excessive 'thumpiness' can be controlled. If it's done in an uncontrolled way (like my attempt to use 3"/75 mm of piezo coax (plus regular coax, total capacitance only 100 pF), feeding a 1M ohm guitar amp, the bass cut was ridiculous, even on a violin...so I made sure my first JFET preamp had the highest input resistors I could find...not aware that circuit noise tends to be proportional to resistance...the hiss was bad, the low end was gone, and it was a bear to shield, even with the coax braid already on it. Obviously Fishman had that figured out, and his stuff works...so much for the DIY'er.

The large ribbon piezo is about 3000 pF all cabled up & shielded & is happy with a 1M ohm guitar amp.

Your mileage and language may vary...Series pickups CAN work, but the signal isn't equal, in part because they are often at two different locations along the strings and can also be unequal if the pickups are drastically different.

An example is paralleling a high-output magnetic humbucker (they usually have higher resistance due to more windings, so people equate magnetic pickup resistance to output) with a single coil magnetic pickup...the single coil one is usually a lot lower impedance and drags the humbucker 'down to its level' significantly...not a dramatically worthwhile combination (see deafeddie.net for more useful conbinations).

If no one else answered yet why one might combine a piezo and a magnetic pickup on the same instrument, the one response of "more tones" can be added to by saying that the piezo picks up the physical vibrations of the body and string for a more acoustic sound (unless you can overdrive electronics with it), and a magnetic pickup picks up primarily the string movement in the pickup's magnetic field. So why do solid and hollow bodied instruments sound so different with similar pickups (implying they seem electrically similar)...my best attempt at a guess is that the string vibration interacts with the physical/acoustical properties of the very different bodies...so the string vibrates differently with the same magnetic pickup on two different instruments.

I've read that a piezo under the top of an instrument (say a violin) picks up string and body vibration, but a sensor in a bridge or under the foot of a bridge gets mostly string vibration...but you can't always get inside an instrument to mount a pickup...except on this website...so you stick it, wrap it, whatever, on the outside.

Hopefully all my rambling is helpful to someone who's still awake after reading it.

I will definitely be posting some my own questions shortly, and trust me, some of them will seem clueless, so maybe that will balance out...

Murray

Permalink Reply by Fergus Morris on May 23, 2010 at 9:58am

Most informative! I am a big fan of making instruments with piezos and magnetic pickups in. I've done it on two instruments, and really like all the different tones it lets me get.

Murray said:

(Un-)solicited electronics rambling...

Evidently putting piezos in series must work, based on what others have said, but not having tried it, based on my initially frustrating experience making an overdrive 'unstomp' box for a violin with naive assumptions about piezo impedance, I will never try series piezos...I had some really bad hum, noise and frequency response issues with the very highest impedance ones (75 mm length of piezo polymer coax), and can't believe how agreeable a large polymer ribbon (~3/4" x 3") piezo has been with everything I plug it into....

A magnetic pickup is (simplified), a coil of wire or inductor. An inductor's electrical property 'L' (inductance) is essentially a constant and independent of frequency. It's impedance (XL=2 x Pi x f x L) however is proportional to (increases) with frequency, so the combination of a magnetic pickup's impedance and a conventional amplifier's input impedance has a general characteristic of a low-pass filter. If you put two identical magnetic pickups in series the combined impedance at a particular frequency doubles in a way that the high frequency rolloff point is cut in half...it may sound less bright, depending on the amp impedance. Inductance and impedance of inductors, and (magnetic pickups) in parallel reduce in a manner similar to resistors in parallel...it is reduced. Paralleled magnetic pickups generally sound brighter. Cable length complicates the issue, but that's a summary.

A piezoelectric sensor (and an electret for that matter) is (simplified), a capacitor. A capacitor's electrical property called capacitance is essentially a constant and independent of frequency but it's impedance is inversely proportional to frequency (decreases with increasing frequency). Because of that inverse dependence of frequency, a capacitor's impedance reduces with increasing frequency Capacitors in parallel ADD in capacitance,the way inductors in series add.
Xc = 1/(2 x Pi x f x C). (Pi, of course being that weird little Greek letter that looks like a Spanish tilda on crutches, that you needed in school to figure out area and circumference of circles before you decided being a professional musician sounded better than geometry.)

When you put capacitors in series their combined capacitance is reduced, and there are not a lot of times it's done. The worst effect this has is that a piezo pickup and the input impedance of an amplifier behave as a high-pass filter. If your piezo impedance is too high for your amp impedance, you will have reduced or poor low frequency response...this is used to advantage with string instruments like bass, cello, etc, in a controlled way, so excessive 'thumpiness' can be controlled. If it's done in an uncontrolled way (like my attempt to use 3"/75 mm of piezo coax (plus regular coax, total capacitance only 100 pF), feeding a 1M ohm guitar amp, the bass cut was ridiculous, even on a violin...so I made sure my first JFET preamp had the highest input resistors I could find...not aware that circuit noise tends to be proportional to resistance...the hiss was bad, the low end was gone, and it was a bear to shield, even with the coax braid already on it. Obviously Fishman had that figured out, and his stuff works...so much for the DIY'er.

The large ribbon piezo is about 3000 pF all cabled up & shielded & is happy with a 1M ohm guitar amp.

Your mileage and language may vary...Series pickups CAN work, but the signal isn't equal, in part because they are often at two different locations along the strings and can also be unequal if the pickups are drastically different.

An example is paralleling a high-output magnetic humbucker (they usually have higher resistance due to more windings, so people equate magnetic pickup resistance to output) with a single coil magnetic pickup...the single coil one is usually a lot lower impedance and drags the humbucker 'down to its level' significantly...not a dramatically worthwhile combination (see deafeddie.net for more useful conbinations).

If no one else answered yet why one might combine a piezo and a magnetic pickup on the same instrument, the one response of "more tones" can be added to by saying that the piezo picks up the physical vibrations of the body and string for a more acoustic sound (unless you can overdrive electronics with it), and a magnetic pickup picks up primarily the string movement in the pickup's magnetic field. So why do solid and hollow bodied instruments sound so different with similar pickups (implying they seem electrically similar)...my best attempt at a guess is that the string vibration interacts with the physical/acoustical properties of the very different bodies...so the string vibrates differently with the same magnetic pickup on two different instruments.

I've read that a piezo under the top of an instrument (say a violin) picks up string and body vibration, but a sensor in a bridge or under the foot of a bridge gets mostly string vibration...but you can't always get inside an instrument to mount a pickup...except on this website...so you stick it, wrap it, whatever, on the outside.

Hopefully all my rambling is helpful to someone who's still awake after reading it.

I will definitely be posting some my own questions shortly, and trust me, some of them will seem clueless, so maybe that will balance out...

Murray

Permalink Reply by Murray on June 13, 2010 at 5:02am

Very cool...

or should say 'chilled to the bone'...haha

Permalink Reply by Bad Golfer on July 18, 2010 at 5:43am

Love it!...great idea !

Permalink Reply by MichaelS Country Boy Guitars on July 19, 2010 at 12:54am

I have just done 3 cbg piezo set ups, one with a single in the box with no insulation at all and one with a double parallel wired in the box also no insulation on the back. These both work well, but if I put my am (roland micro cube) on either of the "stack" simulator settings and get within a few feet I get a squeeling feedback. On the third setup I put 2 piezos in the bridge parallel wired with a brass bar for the strings, the sound is great, but so are the other 2, but absolutly no feedback squele from the amp, I even held the guitar right in front of it!! The bridge is made from 2 thin pieces of mahogany from the inside of a cigar box, the bottom piece is cut out for ther piezos and the top is solid, both glued together. Piezos glues inside and a thin piece of wood glued behind them so they are sandwiched in wood the whole thing is about 5/16s thick. Works great, highly recomended.
On the other 2, the double is quieter thru the amp at the same volume and gain levels than the single piezo, but a more mellow tone.
One more thing, the piezos I used are the 22mm econo piezo from CB Gitty and they work great.

Permalink Reply by Murray on July 19, 2010 at 11:49am

"On the third setup I put 2 piezos in the bridge parallel wired with a brass bar for the strings, the sound is great, but so are the other 2, but absolutely no feedback squeal from the amp, I even held the guitar right in front of it!! The bridge is made from 2 thin pieces of mahogany from the inside of a cigar box, the bottom piece is cut out for the piezos and the top is solid, both glued together. Piezos glued inside and a thin piece of wood glued behind them so they are sandwiched in wood the whole thing is about 5/16s thick."

I like this...a step toward a semi-hollow... CB-335 :O)? You've killed 3 birds with one cigar box...The larger structure of the double keeps the top from giving feedback, the instrument has about half the output impedance of the single configuration, so possibly 6 dB less noise, and your low end starts rolling off at half the freq. of the single.

On the other 2, the double is quieter thru the amp a the same volume and gain levels than the single piezo, but a more mellow tone."

Question on this...from your point of view (or hear), do you get the impression the double has noticeably more bass, the single has apparently inadequate bass, or the double just sounds more balanced, making the single sound deficient?

I'm just curious from a subjective standpoint. I think your findings make me even more opposed to series piezos. Now that you have an integral-pup bridge design you're happy with, I wonder if on your next build you (or someone else) made the wiring accessible to a DPDT switch so you could try both parallel and series wiring on the exact same instrument and amp. One of the problems with telling people what works or doesn't with series pups is that we all have different combinations. You bridge is worth paying attention you - that's obvious to you- you're probably gonna use it from this point on!

I guess I've kicked this horse enough, huh? Nice job!

One more, no, two, more thoughts.

If you have two large piezos and too much bass or the instrument is too sensitive to percussive handling, series wiring would cut the low end for you.


If ya only have one and don't wanna rebuild it and it's got not enough low end, you could reduce the value of your volume control if it's in the instrument by putting a resistor in parallel with the outer leads of the pot...you'll lower the output, but also drop the lower rolloff frequency to a lower point.

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