Don't try and build a non-inverting amp, go for an inverting amp,
QuoteDon't try and build a non-inverting amp, go for an inverting amp,For audio it makes not a jot of difference.
@rlogiaccoThe biasing on the output was fine. It was the input that was not. See the attached diagram, the first one you get when googling.
There is no need for the pot. The -ve end of the 10uF cap should go to the analogue input of the arduino. With a 10K resistor to +5V and another to ground to complete the biasing for the analogue input.The gain is the ratio of the 100K and 1K resistors going to pin 2 of the op amp. So this is a simple X100 gain. Adjust these values for other gains.
This preamp design stuff really isn't as trivial as it may seem.
The pot was there to control the gain
wouldn't I risk to input a voltage higher than 5V
I thought the voltage divider I created on the Arduino side would have ensured isolation and protection to the arduino.
As I said in the title: I need help
QuoteThe pot was there to control the gainNo it was there to control the output level, the gain remains the same. If you want a variable gain make the 100K resistor connected to pin 2 into a variable resistor using one end and the wiper of the pot.
Quotewouldn't I risk to input a voltage higher than 5VNo because the op amp is powered by 5V so it can not produce more than 5V output, no matter what the gain is.
QuoteI thought the voltage divider I created on the Arduino side would have ensured isolation and protection to the arduino.No the two resistors forming a potential divider on the arduino input side that I described is to bias the audio signal, when there is no audio to half the available voltage range. This means when there is a signal it will sit symmetrically between the two voltage rails.
QuoteAs I said in the title: I need helpThat is what we are trying to do.
Make what I told you. Buy an oscilloscope.
you shouldnt need an oscilloscope to make a preamp. it helps, but is not neccessary.
do you have a drawing or picture of what you have currently built? how are you making +/-6V from the 12V?
the only advantage of the inverting amplifier is that it is easier to bias / requires less components/
I don't get this either: isn't the opamp gain given by 1+(R3/R5)? T
Actually I'm powering the opamp with 12V, splitted into +6V and -6V....
you shouldnt need an oscilloscope to make a preamp.
Why do you keep on posting that circuit. I have told you already it will not work because the biasing is none existent on the front end.
When I talk of the pot I was referring to the pot in the correct diagram I posted not your diagram.
QuoteActually I'm powering the opamp with 12V, splitted into +6V and -6V....Why? If you do that you will need protection on the arduino's input. Use two diodes, input to cathode and anode to +5V for one. input to anode cathode to ground for the other.
@rlogiacco - if you are not prepared to take advice then do not ask for it.
the lm358 isnt quite rail to rail, but will be close enough to get you started. i would definitely reccomend starting from scratch with the lm358 and an inverting amplifier. its good to understand what you have done, but you might find it easier to get there if you take smaller steps along the way. if you look a the circuit for the AC inverting amplifier on this pagehttp://www.openmusiclabs.com/testpage/you can just make R1, R3, and R4 10k, R2 100k, and C 1uF, and run everything off 5V.
I'm using 12V because I've read the TL082 needs a negative input voltage and I actually got it somewhat working by using that voltage splitter.
May I ask you which IC would you suggest for my case?
(is it correct to say ground biasing?)
I'm not debating your suggestions
because I'm unable to apply them unless I understand them
you gave me a diagram for an inverting amplifier with a grounded negative supply, which I already tried and it appeared non working for a TL082.
It looks like you want to stay with this wrong thing that you have till you're told what is wrong with it even though you haven't a basis to understand - as you have acknowledged.Given that, why can't you simply "do as you're told"? Is this about ego?You've blindly accepted this bummer circuit that you have now, so what's the problem?
That circuit that Mike attacheduses this TL082.[The two 47K resistors on the non-inverting input "split" the supply.]I don't like the "gain" pot on the output (it's an attenuator that way) and I wouldn't capacitively couple its output either, but those are side issues.