[sdiy] preamps for piezos (slightly OT?)

[Busby Bergson]

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.
> >>>
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