I hope someone can help me invert an analoge varying sine wave signal without amplifying it. I have looked into OP amps but they all seem to give an amplification. I have seen basic diagrams that look like what im looking for though:

Would this work for me? what value resistors / transistor would you suggest? Im working with milivolts, the values given out by an audio pre-amp.

Thanks in advance

 

Use two 100K resistors for R1 and R2.

Have u considered using a low noise op amp since you are working with low voltages?

 

Hello,

With equal resistors you will have a gain of -1.
Take some resistors between 10K and 1M.
The resistor value will be the input resistance.
See this page for more info:
http://www.allaboutcircuits.com/vol_3/chpt_8/5.html

Bertus

 

Ok great thanks - fairly new to opamps, what differences are there? What model would i go in search for?

 

Hello,

I ofthen use the TL071 (single), TL072 (dual) or TL074 (quad) opamps.
I have attached the datasheet for you.
I also attached a kind of opamp handbook.

Bertus

 

Great, thank you! I will use pins 2, 3, and 6 with the stated resistor vaules.
Cheers this forum is brilliant!

 

We give some quick solutions but it doesn't mean they are the best solutions. They will work but there might be better solutions. Keep this in mind as to seek for improvements if required.

 

Hello,

Also keep in mind that the shown circuits will work for dual powersupply.
If you are using a single powersupply, take a look at the attached PDF.

Bertus

 

ahh ok... i am after an amplification of -1, Just inverting the wave really, would this work or would i need a power supply as you say?

 

Are you wanting the response to be down to DC? If so you will likely need two power supplies, although there are ways to fake this.

Creating a Virtual Power Supply Ground

 

the signal is going to range from 15hz to 200hz most likely, its from a subwoofer preout

 

Your circuit in post#9 has the inverting (pin 2) and non-inverting (pin 3) inputs reversed.

 

What is the application for? I'm assuming a subwoofer, do you already have the sub?

The sub for my computer speakers (Sunfire Subwoofer) has a phase adjustment on it from 0-180 degrees. Others I've seen have a switch for 0 or 180 phase shift. Is this similar to what you are trying to achieve?

 

thatoneguy,

I have a subwoofer pre-amp which only gives frequencies below 200hz in the music. This is then connected to the subwoofer amplifier, which is a stereo amp (therefore i have split the single signal from the preamp into two, so they can be plugged into both left and right inputs on the amp). What i am trying to do is invert the signal of ONE of the signals, for example on the left hand side, so that the phase from the positive speaker terminal is reversed. This would mean i could bridge the amplifiers inside by connecting a subwoofer to the two positive terminals of the amp.

I hope this makes sense without a diagram!

PS. i did wonder why pin 2 and 3 were backwards, i got the main image of the opamp from google images like that.

 

I suggest using 10k resistors, as that matches the impedance of line-level audio.

 

Aha, just found something that may work instead:

http://www.jensen-transformers.com/as/as042.pdf

Passive, and does the job, right?