[sdiy] 324 problems

[Sowa Roman]

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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