[sdiy] preamps for piezos (slightly OT?)

[rsdio at audiobanshee.com]

One thing I always try to do is get the data sheets for all critical components. For example, the exact piezo contact mic that you're using hopefully has a manufacturer and part number. If you grab the data sheet for that part, then you'll know its output impedance, capacitance, and any other characteristics that might help fine-tune your preamplifier design.

Richie's suggestion might be a good direction. Just make sure you have some path to ground for the charge so that the integrator doesn't simple charge to one of the rails and then get stuck there.

Brian


On Feb 14, 2016, at 3:10 PM, Busby Bergson <busby.bergson at gmail.com> wrote:
> Right - that's what I was asking about - since the Mikrophonie preamp has the same first stage that I have been working with, I was curious if Jarno's idea was that the second stage would somehow fix the problem.
> 
> Still, though, having tried an LM833, in addition to the TL0xxs - and trying a range of resistors at the input stage from 1m to 20megs - I'm still finding a discrepancy with the bass. 
> 
> I'm wondering if it potentially has to do with the input preamp on the guitar amplifier - perhaps it gets overloaded? 
> 
> On Sun, Feb 14, 2016 at 5:44 PM, <rsdio at audiobanshee.com> wrote:
>> 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.
>> >>>