Double Bass How to make a piezo pickup

[Passinwind]

I've been dong more research and learned the that these film piezo transducers are much less sensitive in compression than the ceramic transducers used by K&K and others, so you can't just sandwhich them under a bridge foot.The trick is to mount them so that they're stretched by the vibrations from the bridge or top, and that's why the cork layer under the transducer is a critical part of ToneRanger's design. I'm looking for some other complient materials that might work. I'm also looking at gluing the film to a stiffer backing, and mounting it so it's bent by vrabration- which will also stretch the film.

Stay tuned ;-)

Cool, consdier me subscribed! I'm getting ready to go to work with another Talkbasser on a couple of DIY EUBs, and the electronics are my responsibilty. I have a friend who builds SONAR transducers, and another one who works with strain gages a lot. I plan to keep whatever I learn from them open source if at all possible.

For fun with acoustics-related materials, try here: http://www.mcmaster.com/

 

[mje]

Cool, consdier me subscribed! I'm getting ready to go to work with another Talkbasser on a couple of DIY EUBs, and the electronics are my responsibilty. I have a friend who builds SONAR transducers, and another one who works with strain gages a lot. I plan to keep whatever I learn from them open source if at all possible.

I was at Rob Wilson's earlier today playing with some transducers and preamps I made, and discussing ways in which we can mount them in his solid body instrruments.

I'm trying to find some PZT piezo cermic materials to play with... suppliers sell large (like 8") squares that are around $100-120. Might have to bite the bullet. Then I need a good way to cut them into tiny dice; preferred method is a diamond saw. Second way is score-and-snap, but that doesn't alwasy produce good results. I'm trying to make sensors small enough to fit into a violin bridge.

 

[mje]

Nice one! Is that fdeck's preamp circuit or something different? Keep us posted on progress with potted electronics - my next solid-body EUB experiment will be with pickups under recessed bridge posts so they connect directly inside the body cavity.
.

It's even simpler than fdeck's- no input resistor. I've done it both ways, and with a pair of resistors to set the bias of the input signal. With 0dB gain (actually slightly less than zero), you have a lot of leeway. I'm also playing with some op-amp designs using FET-input opamps (TL071s) with and without gain.

Putting the FET right on the pickup has some advantages. You can run unsheilded cable from there, if you like, with no hum or noise pickup. An FET and two 1/8th watt resistors can be very small- the capacitors can be mounted far away. WIth SMD devices it could be even tinier... I'm not sure I can work that small, but I have an even smaller Antex soldering iron on order ;-)

 

[jflojazz]

Hi Y'all I have made a bunch of my own pickups it quite fun.
i foung the output to be very low with the piezo film transducers.
You definitely need a preamp with a lot of gain as close as possible to the pickup.
If you do that the tone is great, if you use more than one element be sure to hook them up in paralell or the impedance doubles! Here is a pickup I built for EUB I am selling now.
Mogami Cable is the best.
I have also used piezo buzzers which have a higher output but a
sharper tone. i am currently winding my own magnetic pickups
Which has been a pain in the butt! but now I think I have found a model that is killin!
I will post when its done.

 

[mje]

The ceramic piezo elements haven't arrived yet, so I'm experimenting with getting more gain out of the MSI film elements. I'm also playing around with encapsulating the electronics in eopxy or hot melt glue while I wait for some PC board materials to arrive:

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That glue is tricky to work with ;-)

I built two TL071 based preamps with a little gain built in. The TL071 isn't super quiet, but I think it's quiet enough for this application, and it's an FET-input opamp. I'm going to drop off a few more prototypes at Rob WIlson's shop this weekend for him to experiment with. He's mainly interested in a buffer he can install in his instruments between the pickup and volume control, so rolling off volume doesn't roll off tone, too. We can do that with fdeck's simple source follower/charge amp.

 

[Baird]

Is there any chance that somebody could please post a link to where I could get some high-quality cable on the internet?

 

[ToneRanger]

Here is a pickup I built for EUB I am selling now.

Very tidy! How did you get the cable to join on so neatly? Is there heatshrink involved?

 

[mje]

Is there any chance that somebody could please post a link to where I could get some high-quality cable on the internet?

Good question. I've been using what is essentially RF cable- RG-174 and some smaller teflon stuff, buit what I really need is something smaller and limper, especially for the violin and viola pickups. I con't seem to find what I'm looking for in the Mouser catalog.

I got some tiny PZF crystals today- about 5x2x0.3mm- that I'm going to try to make into pickups. More as this develops.

And Rob Wilson and I installed a one of those neat Gotoh battery boxes that Stew-Mac sells into my Azola Bugbass about an hour ago- it's going to be the test platform for these projects before we install them into his instruments.

 

[jflojazz]

Link Removed
Has Mogami cable for sale.
When using the msi films use needlenose or a wirecutter to pry open the crimps on the supplied leads and then recrimp to a shielded cable.
To make it neat instead of stripping the cable slice it longitudinally and then you can pull out the wire at a right angle.
then no heat shring is necessary to encase the leads.
thats a simple explanation
JF

 

[Aleph5]

Markertek is where I've gotten my wire. I bought type 2944.

 

[mje]

Link Removed
Has Mogami cable for sale.
When using the msi films use needlenose or a wirecutter to pry open the crimps on the supplied leads and then recrimp to a shielded cable.
To make it neat instead of stripping the cable slice it longitudinally and then you can pull out the wire at a right angle.
then no heat shring is necessary to encase the leads.
thats a simple explanation
JF

Couple of great ideas there. Are you using a preamp with gain on the MSI elements?

Interestingly, I found Markertek in a web search earlier today and ordered some tiny Mogami 2-conductor + shield, #2697, as I can use that with active pickups I'm making as well.

 

[fdeck]

The ceramic piezo elements haven't arrived yet, so I'm experimenting with getting more gain out of the MSI film elements. I'm also playing around with encapsulating the electronics in eopxy or hot melt glue while I wait for some PC board materials to arrive:

Link Removed

That glue is tricky to work with ;-)

I built two TL071 based preamps with a little gain built in. The TL071 isn't super quiet, but I think it's quiet enough for this application, and it's an FET-input opamp. I'm going to drop off a few more prototypes at Rob WIlson's shop this weekend for him to experiment with. He's mainly interested in a buffer he can install in his instruments between the pickup and volume control, so rolling off volume doesn't roll off tone, too. We can do that with fdeck's simple source follower/charge amp.

Mje, if you are considering op amps, it is worth trying some of the Texas Instruments CMOS devices. The TLC2201 should be 6 dB quieter than the TL071. It will put you in good company with most of the high end bass preamps on the market. Plus, it is a rail-to-rail device, so you get more output swing before running into clipping. I use it in my more elaborate preamp described at my web page. But nothing gets quieter than a single JFET. The Toshiba 2SK170 is some 18 dB quieter than the TLC2201.

When I use any op amp to drive a cable, I put some kind of resistor in series with the output, say 150 Ohms, just to avoid oscillation when driving a capacitive cable.

Also note that there is a nice piezo preamp circuit at the Jensen Transformer website, and you can use it without the transformer.

 

[jflojazz]

Cool folks, i use both the tiny mogami cable and the slightly thicker model depending on the application.
I find the MSI films practically unusable without a preamp .
A mic preamp with a high impedance input like the art tube Mp
1mohm or the K&K 2 channel.
I like the ideas for the DIY preamps. Bartolini sells and makes
circiuts for piezos too.
That is wHat Dino from BSX basses uses for his on board preamps. they sound great I played an Allegro EUB at a music store, I am saving my money for one of those!

 

[Michael Vee]

I've been following this excellent thread with considerable interest, as I am still trying to figure out how to replace the stock pickup on my Ergo EUB with something better.

I have a couple of the piezo films from Experimental Musical Instruments, but haven't been satisfied with them yet. I will be trying the shielded cable and encasing the films in copper foil.

The fun part, of course, with the Ergos is their non-standard bridge design. The hand-carved bridge sits down in a slot into which you must place a piezo element or film strip, and then route the cable through the original hole into the electronics cavity in the back, where there is a jackplate.

I'm certain that there is a solution that works, which I will have to experiment with and handbuild. The Ergo is a really nice and simple design, and I'm sure the work to replace the stock electronics will be well worth the result.

Where does one find the cork strips mentioned earlier in this thread? I've looked at Lowes and Home Depot with no luck. A craft supply store, maybe, like Hobby Lobby?

 

[ToneRanger]

Where does one find the cork strips mentioned earlier in this thread? I've looked at Lowes and Home Depot with no luck. A craft supply store, maybe, like Hobby Lobby?

I found some gasket offcuts at 'Reverse Garbage', a local recycling centre. You can probably buy gasket material at an auto parts shop. I've also used slices of wine cork (I think Shiraz provides the best tone).

 

[fdeck]

Self adhesive velcro is also a good padding material. You can use the fuzzy side or the prickly side, depending on how squishy you want it to be.

 

[mje]

I found some gasket offcuts at 'Reverse Garbage', a local recycling centre. You can probably buy gasket material at an auto parts shop. I've also used slices of wine cork (I think Shiraz provides the best tone).

The cork gasket material from the auto stores is ground cork mixed with rubber. It's cheap (I think I paid $2.99 for a square foot) and it's pretty tough, but not very compliant; I used a piece to repair the K&K p/u on my Azola, and it involved very careful fitting..I've also tried some material sold for recorking woodwinds.

But the best material I've found is 1/16" cork from the local Rockler woodworking store. Cheap, compliant and self-adhesive.

 

[mje]

The fun part, of course, with the Ergos is their non-standard bridge design. The hand-carved bridge sits down in a slot into which you must place a piezo element or film strip, and then route the cable through the original hole into the electronics cavity in the back, where there is a jackplate. ...

You might try MSI's piezoelectric cable, which has high output and is used by a lot of companies for under-the-saddle pickups. I've found a couple of suppliers selling it for $1/inch. One supplier is [Invalid or Expired Link Removed].

I haven't tried it yet, but I may try it in one of Rob Wilson's electric violins.

 

[mje]

Mje, if you are considering op amps, it is worth trying some of the Texas Instruments CMOS devices. The TLC2201 should be 6 dB quieter than the TL071. It will put you in good company with most of the high end bass preamps on the market. Plus, it is a rail-to-rail device, so you get more output swing before running into clipping. I use it in my more elaborate preamp described at my web page. But nothing gets quieter than a single JFET. The Toshiba 2SK170 is some 18 dB quieter than the TLC2201.

When I use any op amp to drive a cable, I put some kind of resistor in series with the output, say 150 Ohms, just to avoid oscillation when driving a capacitive cable.

Also note that there is a nice piezo preamp circuit at the Jensen Transformer website, and you can use it without the transformer.

Lots of good advice; thanks. I'm mainly sticking with the simple JFET circuits right now since, as you say, they're very low noise, and I can make them very tiny. I wasn't familiar with the TLC2201; I used to use the NE5534 back when I was building audio circuits for my grad school research, which gives you an idea how current I am in op-amp technology ;-)

I also wasn't familiar with rail-to-rail circuit topologies, and read up on that a bit. My op-amp preamps have typically used a single battery, biasing the input with a couple of 1M resistors, so I probably wasn't getting much swing at all.

 

[fdeck]

The 5534 was one of the first respectable audio op amps. It is still quite respectable, and has some clones in widespread use.

It is a bipolar op amp, so it can't be used for a piezo. Even if it could be operated with a high input impedance, the input current noise would eat you alive. In this day and age of high performance IC's, the best choice for a bass preamp front end is often still a Class-A JFET stage with a bit of gain, because it can easily have a noise floor below the self noise of either a piezo or magnetic pickup.

There are low noise JFET op amps, particularly in the Burr-Brown catalog (now Texas Instruments), like OPA121, OPA134, and OPA627, but they are only marginally quieter than my CMOS favorites, and draw obscene amounts of current. It is generally the case that FETs get quieter as you increase their drain current.

The JFET op amps have one other property, which is that they are a lot faster than the low current CMOS chips. But if you are careful how you use the CMOS chips, their relatively low speed is not an issue. There is some more discussion of this in the documentation for my BBBB preamp at:

[Invalid or Expired Link Removed]