Posted by Fergus Morris on February 24, 2010 at 12:28pm
I've seen this done on a few builds, and even did it myself once (though i can't quite remember why I thought it would be a good idea), but what are the benefits of wiring two piezos in series rather than having one single one? Does it increase (double?) the output?
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More testing, I put the single piezo in the bridge instead of in the box, it helped with the feedback. The bridge is an oak flat piece with a wood saddle, the sound is not as loud as the macanudo with double bridge piezo, but the bridge on that is thinner and has a brass saddle. So far the double bridge piezo is best.
The wood sandwich around the single piezo did not cut the feedback squeel.
MichaelS said:
OK, I'll try to answer you. I think the single has inadequate bass and the double has a more balanced tone, to my untrained ears. I am working on getting the squeele out of the single right now by adding a thin wood sandwich around it, we'll see if it works. I would like to try a switch as you mentioned, having both "tones" could be usefull, and if you have two piezos why not.
Murray said:
"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.
OK, I'll try to answer you. I think the single has inadequate bass and the double has a more balanced tone, to my untrained ears.
I am working on getting the squeele out of the single right now by adding a thin wood sandwich around it, we'll see if it works.
I would like to try a switch as you mentioned, having both "tones" could be usefull, and if you have two piezos why not.
Murray said:
"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.
"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.
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.
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...
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...
Replies
http://www.electrocoustic.com/magpi.html
uses twin piezos in parallel and a blend pot
Don
MichaelS said:
I am working on getting the squeele out of the single right now by adding a thin wood sandwich around it, we'll see if it works.
I would like to try a switch as you mentioned, having both "tones" could be usefull, and if you have two piezos why not.
Murray said:
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.
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.
or should say 'chilled to the bone'...haha
Murray said:
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
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