[sdiy] preamps for piezos (slightly OT?)

[Richie Burnett]

For a piezo sensor aren't you supposed to use a charge amplifier?  People at 
work use them for vibration analysis in the field of Mechanical Engineering. 
Google "piezo charge amplifier".  This has an integrator response so it 
would tend to boost the bass frequencies and attenuate the highs.  Might be 
what's needed???

-Richie,

-----Original Message----- 
From: rsdio at audiobanshee.com
Sent: Sunday, February 14, 2016 10:44 PM
To: synth-diy DIY
Subject: Re: [sdiy] preamps for piezos (slightly OT?)

Unless the second stage is an EQ, you're not going to regain any lost bass.

The problem is that the first stage is acting as a high pass because of the 
passive components ahead of the first op-amp, and the input characteristics 
of the op-amp. Changing the loading and op-amp type should fix this.

The Mikrophonie preamp already has two stages.

Brian


On Feb 14, 2016, at 2:35 PM, Busby Bergson <busby.bergson at gmail.com> wrote:
> a second pre-amp stage might recover some of the lost bass frequency?
>
> On Sun, Feb 14, 2016 at 4:47 PM, jarno.verhoeven at ziggo.nl 
> <jarno.verhoeven at ziggo.nl> wrote:
>> Yes, I saw this in the schematic, maybe mine was an older version. But 
>> that schematic is a fine starting point.
>>
>> ------ Origineel bericht------
>> Van: Busby Bergson
>> Datum: zo, 14 feb. 2016 21:08
>>
>> Hi there -
>>
>> The "Mikrophonie" preamp looks very similar to what I'm building: 
>> http://musicthing.co.uk/modular/wp-content/uploads/2014/06/Mikrophonie-2-2-Schematic.pdf
>>
>> Though I'm not using any sort of input cap (nor does the schematic) - 
>> that would potentially serve as something of a high-pass, wouldn't it?
>>
>> I am also using a TL084, which does have JFET inputs, correct?
>>
>> Perhaps it is a matter of experimenting with other ICs.
>>
>> On Sun, Feb 14, 2016 at 2:22 PM, Olivier Gillet <ol.gillet at gmail.com> 
>> wrote:
>>> The choice of op-amp matters. Bipolar op-amps have a low input
>>> impedance (a few hundred k) which could have an impact on bass
>>> response. An op-amp with JFET inputs would be a better choice here.
>>>
>>> On Sun, Feb 14, 2016 at 7:20 PM, Busby Bergson <busby.bergson at gmail.com> 
>>> wrote:
>>> > hi synthdiys,
>>> >
>>> > i'm currently experimenting with contact mics. they sound pretty good 
>>> > going
>>> > into a guitar amplifier, directly - but if i want to send them through 
>>> > my
>>> > other circuitry, it seems that they require a specialized 
>>> > preamplifier, to
>>> > compensate for their impedance.
>>> >
>>> > i've been using something along these lines:
>>> > http://music-electronics-forum.com/attachments/4228d1232615609-non-invert.buffer.gif
>>> >
>>> > however, i'm noticing that there is still a significant high-passing -
>>> > compared to the bassier direct-to-guitar-amplifier arrangement.
>>> >
>>> > any thoughts?
>>> >
>>> > -  b.b.
>>>
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