[sdiy] 324 problems

[Scott Bernardi]

One other thing; if you use single supply, you'll probably also want to ac
couple the input resistor and output with a series capacitor.   Otherwise
you'll need to provide a dc level to your input signal (like a sine wave
riding on top of a 4.5v dc voltage).  You choose the value of the input and
output caps according to the lowest frequency you want to amplify:  C = 1 /
2*pi*R*f  where R in the input resistor, or the load resistance that the
opamp sees.




Sowa Roman wrote:

> first you must feed the input via resistor, not directly to noninverting
> input. Gain you get on output is simple to calculate:
> G=Rf/Ri, where Rf is your feedback resistor value, and Ri is value
> of resistor at input. Plus, you get phase reversal, so it should be
> G=-Rf/Ri, but soundwise it doesn't matter.
> Now the supply. If you supply only positive side and want 324 to play,
> you have to apply input signal which is below ground, meaning
> negative voltage. Then, depending on this voltage and your circuit
> gain, you may set the output voltage to a value where opamp will
> sound as it should. Better way to do this is to connet noninvering
> input not to ground but in the middle of two resistors connected in
> series from ground to positive supply. This will set 'artificial' ground
> for 324 into 4.5V (assuming they are same resistors).
>
> Roman
>
> ""-----Original Message-----
> ""From: the-h at mail.utexas.edu [mailto:the-h at mail.utexas.edu]
> ""Sent: Thursday, January 10, 2002 9:01 AM
> ""To: synth-diy at dropmix.xs4all.nl
> ""Subject: [sdiy] 324 problems
> ""
> ""
> ""hey all you vets and smart guys ive got a problem with
> ""something, ive been
> ""trying to make some simple stuff with a 324 quad op-amp but
> ""running into
> ""problems with the chip. The simplest design ive tried to make
> ""is a simple
> ""inverting amplifyer. As far as i know to do this you take the
> ""noninverting
> ""imput of the amp and ground it. then you hook the signal up
> ""to the inverting
> ""input then put a little feedback loop with a resistor, the
> ""larger the resistor
> ""the more the gain (up to the max power). Then of course you
> ""have to power the
> ""op amp to do this i use a 9 volt battery, the 324 is supposed
> ""to be able to
> ""work without a polarized power supply so i just hook the
> ""positive of the
> ""battery with the positive in pin of the amp and the negative
> ""with the ground
> ""pin. depending on which of the 4 internal amps i use i either
> ""get a very quiet
> ""sound or just noise. What am i doing wrong? or is my chip
> ""just screwed?
> ""
> ""
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--
Scott Bernardi
sbernardi at attbi.com