..this should work right? question

[jonny]

Okay so i'm just trying to make a simple op amp circuit here but can't get it to work!! I can't figure out why?
I have R1=R2=150k which should give a gain of 2, all i get is a volt or so dc on the output(of op amp). I'm using an NE5532 also tried 4558 not that it should matter?
I have tested voltages on the op amp seem okay, ie 9v and ground. Also Vcc/2 =4.5V but   ?


(I also have the usual DC blocks 1M and 1u caps on the input and output.)

[The Tone God]

Make another Vcc/2 network and connect to the "+" pin after the input cap.

Andrew

[Derringer]

Make another Vcc/2 network and connect to the "+" pin after the input cap.

Andrew

you should be able to use the original voltage divider though .. no need for a new one right?

and whatever you connect the + input with to Vcc/2 will set the input impedance of the circuit

[Gurner]

Just to add a little bit more - the opamp needs DC biasing on the +ve pin.

Connect a resistor from the opamp +ve input pin to your VCC/2 point .....if it's for a guitar, make sure it's a high value resistor (eg 470k plus), if the input to your opamp is from another circuit, the value of the resistor you use can be much less.

[jonny]

Aha, thanks! I forgot that. I think that was it, I still have a lot of noise/ oscillations for some reason might be my breadboard i'm not sure (it was doing it on another circuit)? Hopefully I can sort it out now. Would a resistor in series before the input cap help?

[edvard]

OK, a few parts are missing.
1 Meg from (+) input to Vcc/2.
Capacitor between R1 and Vcc/2 (.01 to 10uf, to taste).
Elec Cap (22uf - 100uf) from Vcc/2 to Ground (for good measure)