[sdiy] preamps for piezos (slightly OT?)

[bbob]

So would something like your Guitar Preamp (
http://www.till.com/articles/GuitarPreamp/index.html) work, Don?

b

On Mon, Feb 15, 2016 at 11:59 AM, Donald Tillman <don at till.com> wrote:

>
> On Feb 14, 2016, at 10:20 AM, Busby Bergson <busby.bergson at gmail.com>
> wrote:
>
> 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.
>
>
> "Compensate" isn't the best word, but...
>
> Piezoelectric pickups have a very high impedance that's mostly
> capacitive.  That means that if they are loaded down, you'll lose the lows
> first.  Compare that to an inductive electromagnetic guitar pickup which
> loses the highs when loaded down.
>
> So you'll want a preamplifier with an input impedance of 1 Mohm or higher,
> and the higher the input impedance the better the low end response.  It's a
> good place for an FET.  You probably don't need much voltage gain, maybe
> 10dB worth, but that varies wildly with the specific application.  So no
> specialized preamp is necessary, just a very high input impedance.  (Guitar
> amps generally have an input impedance of 1.0 Mohm.)
>
> There's also the other extreme... with a sufficiently high load impedance
> a piezo response can go down to almost DC.  Which means that for an
> instrument like a guitar, the string plucks can induce DC thumps, and it
> might be appropriate to filter those out for your application.
>
>   -- Don
>
> --
> Don Tillman
> Palo Alto, California
> don at till.com
> http://www.till.com
>
>
>
>
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