Double Bass Piezo pickups - how to care for

[ctrlzjones]

I have learned that piezos not only have a quack but also a limited lifespan. Regardless I got me a KNA-DB1 and wonder how to get the most out it.

Is it recommended to leave it in place or to take it on/off?

 

[sean_on_bass]

Personally i dont concern myself with attempting to prolong the life of the piezo and just leave it on the bass. Also with bridge wing pickups you find a sweet spot for the tone you want and you don't want to have to rediscover that each time you play.

 

[Francois Blais]

There are a lot of decades old Underwood pickups still around and working great.
Guess it depends on the construction moreso than being piezos.

 

[Neon Scribe]

I think lifespan is the wrong way to think of it. Piezo crystals are fragile. They may last for decades but they can fail any time. They don't wear out from use, they just break.

 

[Don Hergert]

If it's under pressure, like a piezo usually needs to be in order to pickup sound vibrations, and if that pressure is ever too much or in the wrong place, the crystal can break. They are not quite as brittle as a thin piece of glass.

I carry a backup of my piezo set in my bag. I've never had to use it, but it's there.

Not necessarily a plug for Vic's, but my Model C bridge wing and fingerboard piezo set is $45(US), and there's no lack of quality in these. Easy enough to order two.

 

[jlmorgan84]

The only time I've ever broken a piezo (Lifeline) was accidentally bending it taking it off a bass. There shouldn't be that much pressure on the KNA DB-1 anyway, just enough to hold it firmly in place. Leave it in and don't sweat it!

 

[Wasnex]

IMHO the best maintenance is leave it alone. All of the failures I have experienced were with pickups that were repeatedly moved from bass to bass.

As far as the quack. The ideal impedance varies, with the type and size of the piezo, but generally 1meg is the lowest you should use. Don't think assume that having a super high impedance is always the right answer. It may be, but usually it's not.

Common knowledge seems to suggest that 10meg is the best for piezos, but this can be too high. When the impedance is too high it decreases damping, so the pick has more of a tendency to ring. AFAIK this can result in peaks in the frequency response and a greater tendency towards feedback. AFAIK the ideal value usually falls between 1-5meg.

If the value of your preamp's input impedance is within an acceptable range, but the sound is still quacky. The installation may be the problem. Also, some degree of corrective EQ is beneficial with many piezos, to even out the frequency response. Corrective EQ generally must be increased as the amount of amplification goes up.

 

[Ric Vice]

Just my own anecdotal research tells me that it's better to install them and leave them on the bass. Even with that consideration, depending on the angle of the strings over the bridge, Realists can fail after 4 years. Which is
my experience. That's one of the reasons, I use the Ehrlund EAP because the piezo membrane inside it's triangular shell isn't squeezed between one of the bridge wings, under one foot of the bridge, or between one of the adjusters
and the inside of one of the feet. So far, the Ehrlund's have good longevity, (knock on wood) Of course this only works if you like the sound of the EAP on your bass. Just my take.

 

[Francois Blais]

The Ehrlund EAP is advertized as a microphone, and I didn't find the word "piezo" anywhere in its documentation, so I'm not sure it's a piezo at all.

 

[Wasnex]

The Ehrlund EAP is advertized as a microphone, and I didn't find the word "piezo" anywhere in its documentation, so I'm not sure it's a piezo at all.

Pretty sure this is the patent for the EAP:
WO2004105427A1 - Piezoelectric microphone - Google Patents
WO2004105427A1.pdf (storage.googleapis.com)

 

[Ric Vice]

The Ehrlund EAP is advertized as a microphone, and I didn't find the word "piezo" anywhere in its documentation, so I'm not sure it's a piezo at all.

As I understand it the EAP is a piezo film transducer of some sort. Double MIDI can explain.

 

[Francois Blais]

Ok, thanks for the info.
I trust you!

 

[CryingBass]

Yeh. My Geranium Diode radio broke a few years back too...

 

[DoubleMIDI]

I read a patent years ago and thought or read that it was piezo film material. I might haven’t read it in detail, but it might also have been a different one.

But it seems the link by Wasnex is correct. It says something about a metal sheet covered with a piezoelectric layer.
But the patent doesn’t need to describe the actual EAP exactly. It is still possible that they use piezo film (which is not a ceramic material but a synthetic one).
Synthetic piezo film is less stiff than a piezo coated metal sheet, but the metal might be needed if the amplitude of the contact point is too high for a (weight loaded) piezo foil to follow without distortion.

The Japanese MSP contact pickup (AFAIK) has a circular ceramic piezo disk as the transducer. Probably also with a weight on the center to add inertia to enhance the excursion of the disk.
It doesn’t sound as good as the EAP, but using the same preamp (of the EAP) it sounds just slightly different.

 

[Ric Vice]

Ok, thanks for the info.
I trust you!

Thanks, Francois

 

[Francois Blais]

The Japanese MSP contact pickup (AFAIK) has a circular ceramic piezo disk as the transducer. Probably also with a weight on the center to add inertia to enhance the excursion of the disk.
It doesn’t sound as good as the EAP, but using the same preamp (of the EAP) it sounds just slightly different.

Interesting!
Does that mean the Ehrlund preamp is not linear but voiced for the EAP?

 

[Wasnex]

Interesting!
Does that mean the Ehrlund preamp is not linear but voiced for the EAP?

AFAI the preamp is flat, but the input impedance of the preamp modifies the response of the piezo. So the preamp is not voiced, but it does have some impact on the resultant sound. I assume Ehrlund chose the specific input impedance of the preamp (4.7meg) because he felt it was optimal for the pickup.

Here is a relevant post: Ehrlund pickup with other brand's preamps

 

[DoubleMIDI]

The MSP is advertised to work without a preamp. But I think it works better with a piezo buffer. I just wanted to use the same preamp for both pickups, so the choice was easy to use the EAP preamp for each of them.
As far as I know there is no voicing in the EAP preamp, just a flat frequency response. I think someone here on Talkbass even measured the frequency response and posted a graphic.

 

[Ric Vice]

Yes, years ago Durb (Les) did, I just happed to bookmark it. So here's the scoop

An Ehrlund blog, sort of

"The picture above shows the spectrum of the Ehrlund pre between 0 Hz (DC) and 200 Hz with the switch set to "LOW." The vertical cursor is sitting at 20.5 Hz:



Note that the response is essentially flat down to below 20 Hz. I measured the response as being ruler flat up to at least 10 kHz. Changing to the "HIGH" setting increased the gain by [DEL]6[/DEL] 7.3 dB with no effect at all on the spectrum. There you have it, folks.

Now, unless there is a passive front-end filter designed to interact with the microphone itself, then there is no evidence of a high-pass roll-off anywhere near 40 Hz on either setting"

 

[Wasnex]

Yes, years ago Durb (Les) did, I just happed to bookmark it. So here's the scoop

An Ehrlund blog, sort of

View attachment 4495470

"The picture above shows the spectrum of the Ehrlund pre between 0 Hz (DC) and 200 Hz with the switch set to "LOW." The vertical cursor is sitting at 20.5 Hz:



Note that the response is essentially flat down to below 20 Hz. I measured the response as being ruler flat up to at least 10 kHz. Changing to the "HIGH" setting increased the gain by [DEL]6[/DEL] 7.3 dB with no effect at all on the spectrum. There you have it, folks.

Now, unless there is a passive front-end filter designed to interact with the microphone itself, then there is no evidence of a high-pass roll-off anywhere near 40 Hz on either setting"

This stuff is a bit over my head...but here is another part of the story, that I will try to explain to the best of my ability. Remember I said the EAP preamp has flat response. I also said the input impedance of the preamp has an impact on the response of the pickup.

Piezo pickups have internal capacitance that is determined by the construction of the pickup. The point is different pickups have different amounts of capacitance.

A high pass filter is formed with a capacitor and resistor.

The capacitance of the piezo pickup is shown with C and the input impedance of the driven device is shown with R. The driven device is what the pickup is plugged into...for example a preamp.

This is the frequency response of a high pass filter. The breakpoint is where the response is down by -3dB. When we say the frequency of a high pass filter, the breakpoint is what we are talking about.

As the value of R goes down, the breakpoint of the high pass filter goes up.

Here is a high pass filter calculator: High Pass Filter Calculator (learningaboutelectronics.com)

Let's assume a piezo pickup with 10nF of capacitance. Per the calculator, if the input impedance of the driven device is 1meg, the breakpoint is 15.9hz. However, if the input impedance is lowered to 220K, the breakpoint rises to 72.4hz.

Next let's assume a different piezo pickup with 2nF of capacitance. Per the calculator, if the input impedance of the driven device is 1meg, the breakpoint is 79.6hz, and if the input impedance is lowered to 220K, the breakpoint is 361.9hz.

With the 2nF capacitance, obviously we need a higher input impedance if we want response to at least 40hz or so. Per the calculator the required input impedance is nearly 2meg.

FYI...this is a cut and paste from the Ehrlund tech specs on the preamp:

Frequency Response 5 Hz - 160 kHz ± 1 dB​

The frequency response for the pickup is not provided, but we do know the input impedance of the preamp is 4.7meg, which is fairly high. Using a preamp with a lower 1meg input impedance may noticeably degrade the low frequency response you get from the EAP...but of course we do not know how much capacitance the EAP has, so we can't say for sure.