Experiments with Piezo Discs

PhilKing

If it buzzes, you could possibly pull the piezo wires through a screened cable with the core taken out (if they are small enough), this would save resoldering them.  

BillDL

I always smile when I see pickup systems that use piezo-ceramic discs and cost a lot of money.  Way back in the mid 80s I received a musical birthday card that probably cost my ex about £8 and I found that one of those discs was being used as the sounding transducer between the layers of cardboard.  Tandy (Radio Shack in US) was the go-to place for electronic hobbyists at that time and Maplin stores were sparsely scattered. I bought a selection of piezo-ceramic discs from Tandy to experiment with. I had to solder my own wires onto them and I ruined a handful in the process.  On the ones that worked I stuck a dab of epoxy to secure the thin wires to the edge of the brass plate and stop them being tugged off.

I obviously was already aware of contact pickups like Schaller "Oysters", Barcus Berry stick-on cubic blocks, and so on, otherwise I probably wouldn't have had my eureka moment after finding the disc inside the card.

They came in different sizes with correspondingly different resonant frequencies when used as sounders.  I used thin double-sided tape with fairly low adherance to experimentally position them on the underside of guitar tops and used different size/frequency ones to see whether some would suit the positioning better than others (i.e. better for the bass or treble side).  Once I was happy that I was getting the best results possible I carefully removed the tape and stuck them permanently in place with fast dry epoxy that doesn't dry quite as rock hard as the slow dry stuff.

My first experiment was with a lower priced but fairly good classical guitar. I positioned a large disc about 2.5 inches forward of the bridge on the bass side and roughly midway between the edge of the bridge and the saddle, and positioned a smaller one partly under the front edge of te bridge on the treble side almost in line with the edge of the bridge.  That permutation gave the best overall results.  I am not an electronics wizard, so I am unsure whether it was just the diameter of the disc that made the larger one work better on the bass side or whether the resonant frequency (when used as a sounder) had anything to do with it.  I suppose that those two aspects are closely linked anyway.  I cannot recall with certainty, but I think the smaller diameter ones has slightly thinner brass bases than the larger ones, so perhaps that affected the choice of placement as well.

Used in completely passive mode and without volume or tone pots to tame the response, that guitar put out enough signal to push the front end of a 60 watt solid state amp to "crunch" distortion on clean mode if played hard. It was very punchy and, even though it did sound slightly "woody", it was very susceptible to feedback because the discs were on parts of the top that moved a lot I didn't have an acoustic amp at that time, but my later purchase of a Boss GE-7 helped me to shape the tone.  The annoying aspect was that any accidental contact with the top was picked up , and playing Flamenco golpe (fingertapping) would have sounded like minor explosions through the amp.  With hindsight I should probably have positioned the discs under the saddle to mitigate some of the feedback and top sensitivity.

I had more success with an old smashed up early 70s Fender acoustic that I repaired and refinished.  I used 3 discs closer in to the bridge area and added passive volume and tone pots.  One of the things that tamed the response was how I secured the discs.  I used glue that didn't dry rock hard and remained with a slightly rubbery consistency and, when gluing the discs, I kind of floated them on a thin layer rather than pushing them hard onto the top. That very thin spacer between the top and the disc reduced the attack that was just a bit too harsh when directly in contact with the top.

An ex-friend and I stuck them inside his drum shells and chanelled them through an old Moog synth so that he could gig with bands that did more electronic sounding music.  I made one of those foot tapping wedges that you can now buy commercially to accompany yourself, and I used one of those discs inside that.

Andyjr1515

BillDL said:

They came in different sizes with correspondingly different resonant frequencies when used as sounders.  

I had more success with an old smashed up early 70s Fender acoustic that I repaired and refinished.  I used 3 discs closer in to the bridge area and added passive volume and tone pots.  One of the things that tamed the response was how I secured the discs.  I used glue that didn't dry rock hard and remained with a slightly rubbery consistency and, when gluing the discs, I kind of floated them on a thin layer rather than pushing them hard onto the top. That very thin spacer between the top and the disc reduced the attack that was just a bit too harsh when directly in contact with the top.

Interesting stuff, @BillDL ;

As you say - it would be interesting to know whether the different frequency response actually makes a difference, or whether all of the sizes actually covers the range that is important to a guitar.

And also interesting ref the glue...I might stick with (forgive the pun) double-sided rather than venture to CA

BillDL

I've never actually taken one of those Oyster contact transducers apart to see what's in them and how the transducer element is fitted in relation to the flat surface that goes against the instrument.  I would be curious to know whether there is a spacer of any kind or if the element is right on the inside of the flat metal "foot".  I have an old Schaller one that has a damaged cable, but I'm sure it still works and just needs new cable, so I don't think I'll be trying to take it apart.

One other thing I've seen popping up in electronic supplier websites recently is Piezo-Electric film.  It seems as though the actual film transducer comes covered with flexible plastic like paper laminating pouches and with small spade connectors.  The thing I don't know yet is whether they work in passive mode as vibration sensors or if they need a circuit of some kind:

https://www.azosensors.com/article.aspx?ArticleID=177

https://www.designworldonline.com/the-wonderful-world-of-piezoelectric-film/

sev112

BillDL said:

I always smile when I see pickup systems that use piezo-ceramic discs and cost a lot of money.  Way back in the mid 80s I received a musical birthday card that probably cost my ex about £8 and I found that one of those discs was being used as the sounding transducer between the layers of cardboard.  Tandy (Radio Shack in US) was the go-to place for electronic hobbyists at that time and Maplin stores were sparsely scattered. I bought a selection of piezo-ceramic discs from Tandy to experiment with. I had to solder my own wires onto them and I ruined a handful in the process.  On the ones that worked I stuck a dab of epoxy to secure the thin wires to the edge of the brass plate and stop them being tugged off.

I obviously was already aware of contact pickups like Schaller "Oysters", Barcus Berry stick-on cubic blocks, and so on, otherwise I probably wouldn't have had my eureka moment after finding the disc inside the card.

They came in different sizes with correspondingly different resonant frequencies when used as sounders.  I used thin double-sided tape with fairly low adherance to experimentally position them on the underside of guitar tops and used different size/frequency ones to see whether some would suit the positioning better than others (i.e. better for the bass or treble side).  Once I was happy that I was getting the best results possible I carefully removed the tape and stuck them permanently in place with fast dry epoxy that doesn't dry quite as rock hard as the slow dry stuff.

My first experiment was with a lower priced but fairly good classical guitar. I positioned a large disc about 2.5 inches forward of the bridge on the bass side and roughly midway between the edge of the bridge and the saddle, and positioned a smaller one partly under the front edge of te bridge on the treble side almost in line with the edge of the bridge.  That permutation gave the best overall results.  I am not an electronics wizard, so I am unsure whether it was just the diameter of the disc that made the larger one work better on the bass side or whether the resonant frequency (when used as a sounder) had anything to do with it.  I suppose that those two aspects are closely linked anyway.  I cannot recall with certainty, but I think the smaller diameter ones has slightly thinner brass bases than the larger ones, so perhaps that affected the choice of placement as well.

Used in completely passive mode and without volume or tone pots to tame the response, that guitar put out enough signal to push the front end of a 60 watt solid state amp to "crunch" distortion on clean mode if played hard. It was very punchy and, even though it did sound slightly "woody", it was very susceptible to feedback because the discs were on parts of the top that moved a lot I didn't have an acoustic amp at that time, but my later purchase of a Boss GE-7 helped me to shape the tone.  The annoying aspect was that any accidental contact with the top was picked up , and playing Flamenco golpe (fingertapping) would have sounded like minor explosions through the amp.  With hindsight I should probably have positioned the discs under the saddle to mitigate some of the feedback and top sensitivity.

I had more success with an old smashed up early 70s Fender acoustic that I repaired and refinished.  I used 3 discs closer in to the bridge area and added passive volume and tone pots.  One of the things that tamed the response was how I secured the discs.  I used glue that didn't dry rock hard and remained with a slightly rubbery consistency and, when gluing the discs, I kind of floated them on a thin layer rather than pushing them hard onto the top. That very thin spacer between the top and the disc reduced the attack that was just a bit too harsh when directly in contact with the top.

An ex-friend and I stuck them inside his drum shells and chanelled them through an old Moog synth so that he could gig with bands that did more electronic sounding music.  I made one of those foot tapping wedges that you can now buy commercially to accompany yourself, and I used one of those discs inside that.

Fabulous - learned a lot from that, very interesting 

Andyjr1515

OK - my phone won't play ball at the moment to let me download the 'inside the sound chamber' shots that show that all three piezos did actually end up in the right place!

So that bit of the cunning plan did indeed work

But the answer was this time round a total lemon   No signal was coming through at all!

Now - it didn't take long to find out why...and it's answered one of the questions, that is, does the epoxy back on the commercial ones make a difference?

Yes it does. 

I added a shielded wire to each disc but took heed of @ICBM 's point and cut the piezo wires to about a cm long so I could get shielding close to the discs but not solder to the discs themselves.  But those three shielded wires did weigh quite a bit.

When I investigated why I wasn't getting any sound at all through the amp, I realised that every earth wire for the three discs had snapped off.  So, if for nothing else, the epoxy is probably needed to protect the solder joints of what is very small gauge wire for any normal handling.

So next try is same thing but leave full length piezo wires (unshielded) and just shield the run to the jack with the heavier shielded wire.

I'll use my camera this time but therefore won't be able to take the 'inside the sound chamber' shots

Costings so far:

Excellent K&K Pure Mini - £99
Fitting (based on last one I fitted) 45 mins at minimum living wage of £8.91/hr <It's a hobby to me so it's actually usually £0 but for a true comparison it's worth including this >  £6.68
Total: £106.68
Result:  10/10  

On-the-cheap AJR1515 Pure Speculation
Piezos   £0.75
Shielded Wire: £1.00
Switchcraft Acoustic Barrel Jack: £14.00
Labour 3 hrs at minimum living wage of £8.91/hr  Total So Far: £42.48
Result: 0/10

Hmmm   










 


 

ICBM

Andyjr1515 said:

When I investigated why I wasn't getting any sound at all through the amp, I realised that every earth wire for the three discs had snapped off.

It's a good thing they all did - if only one or two had broken, it would have worked but you would probably have wondered why it didn't sound very good or wasn't very balanced.

Getting the discs off again will be the tricky bit .

Andyjr1515

ICBM said:

Getting the discs off again will be the tricky bit .

Not bad.  Thank heavens for single edged razor blades

Next three are ready to fit and try again

DartmoorHedgehog

I had a cheap (about £3) clip-on piezo pickup that I could never get to work very well clipped onto the sound hole as intended (actually it wasn't too bad on violin f-hole but rubbish for guitar).  Recently I wanted to fit a pickup to my acoustic and was looking at buying one, but decided there was nothing to lose by experimenting with the transducer out of the cheap pickup.  So I cut off the clamp, wired it to a jack socket and experimented with positioning under the bridge plate - it sounds really quite good with the transducer way over on the bass side - if anything still a bit bright, but that can be sorted with EQ on the (external) preamp.  I just superglued it to the underneath of the bridge plate when I was happy with the position.  Would be easy enough to swap it for a better pickup but at the moment I'm completely happy with the results - and the most expensive part of the conversion was the endpin jack socket.

JayGee

Hmmm…. 

Could you drill a couple of small holes through the bottom of the slot the bridge saddle sits in (and the top of the guitar as well of course) and then push a couple of pins through to act as locating points for a jig to fit the discs? 

If you put the discs on some kind of carrier (like a thin strip of Magic Tone Wood?) it could even form part of the permanent mounting.

Or would drilling even tiny holes be considered unacceptably intrusive…?