[sdiy] question: a simple blend circuit?

[harrybissell]

Hi Daniel (inline)

Daniel Englbert wrote:

> >The piezo should probably be buffered first, simple transistor or fet
> >should do, then the
> >pot blend trick WILL work.
> >
> >You can arrange the battery so that the circuit is powered when the
> >guitar (mono) cable is
> >inserted just like in the pedals...
>
> sorry for my ignorance, but what exactly does it mean to buffer the piezo?

Buffer is a circuit that does not change the gain (amplify or attenuate) but
changes
the amount of current that that circuit can produce.   The buffers you are
looking at on
Muzique have high input impedances (roughly 500K and up) and LOW output
impedances
(prlly 3.3K or so)

This means that the piezo will see a high impedance, improving the low frequency
response
(in this case)... and the blend pot will see a low input impedance... a win-win
situation

(the loser here is the added battery you need ;^)

The problem with the 500K pot is not the pot itself. 500K is prlly high enough.
But when the
wiper of the pot is connected fully to the piezo end... whatever load is on the
guitar output
will be right across the piezo - could be a s low as 10K in some cases.

The buffer would fix this.

> it looks like the third one down ( http://www.muzique.com/lab/buffers.htm )
> mentions use for piezo's
>
> but i'm terrible at figuring out schematics... part layout diagrams i can do
> :)

These are pretty easy circuits... if you want to twist one up I could draw a
parts diagram
for you. It would assume you'd use a small piece of .1" perforated PB board.
The HARDEST
thing to get right will be the pinout of the transistor you use. contact me
offlist if you want to
go for it

>
>
> is Q1 a transistor or a jfet? what kind?

its a Jfet in some cases and bipolar transistor in others, see the text right
across from each
example.

> oh well, maybe i'm in overmy head:)

everyone starts there. yes ???

(I'm working on some 1/X circuits for pitch to voltage extraction... I'm over my
head :^)

H^) harry

>
>
> thanks a lot for all the links and ideas!!
> -dan
>
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