# Combining Two Op-Amp Circuits

Discussion in 'The Projects Forum' started by shaheenster, Mar 13, 2014.

1. ### shaheenster Thread Starter New Member

Mar 13, 2014
6
0
Hey guys, was hoping you could help me figure out a fix.

The circuit on the left takes a signal, amplifies it to saturation of around -5 to 5 volts, and then runs it though a rectifier.

The circuit on the right takes a signal and amplifies it to saturation of 1 to 10 volts.

I want to somehow use the second circuit to amplify the first circuits output from the rectifier to around the same amount (1-10 volts) to power my led strip, but i have no clue how...

Thanks for the help!!!!

2. ### shaheenster Thread Starter New Member

Mar 13, 2014
6
0
Ok so I found out how to connect the recifier to the input of the second amplifier,

Now what Im trying to do is make the circuit run off 1 power supply, rather than two 12 volt power supplies. When I connect the first supply to replace the second circuits supply, the circuit doesnt work. It just outputs a solid 1 volt.

http://i62.tinypic.com/2w6v22q.png

3. ### GRNDPNDR Well-Known Member

Mar 1, 2012
519
15
post the multisim file for me, i'd like to take a look, I think it has something to do with how you're powering the opamps.

Mar 13, 2014
6
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here ya go !

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5. ### kubeek Expert

Sep 20, 2005
5,452
1,036
I am really not sure why would you want to do that. Saturated output will produce a square wave centered around 0V. Now if you full-wave rectify it, what do you get on the output? It will be +5V with very narrow negative goind dips, so almost truly +5V DC. I doubt that is what you really want from that circuit.

6. ### AnalogKid AAC Fanatic!

Aug 1, 2013
7,558
2,142
What are you trying to achieve? You said something abut powering LEDs. Are you trying to make them blink at 1 Hz? Vary the brightness up and down? Your schematic has enough parts to do several different things; without some direction toward a goal, we can't help much.

ak

7. ### GRNDPNDR Well-Known Member

Mar 1, 2012
519
15
Didn't know it was multisim 13... I'll have to look into upgrading now since my latest version is 12 and I haven't used it in a while.

8. ### shaheenster Thread Starter New Member

Mar 13, 2014
6
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Yep, so my main idea was to take the bass notes of my audio jack output, and use it to drive LEDs with an opamp.

Problem was that since im looking at the really low frequencies, my leds would just end up blinking at around 1-10hz which is not what I wanted. Because of that I added the rectifier and some capacitors to smooth the output to something that is around 3.5 volts dc.

Thing is that the leds are meant to run off 12 volts, so 3.5 is not enough. So the second cricuit was added to make the output from 3 ish volts to around 10 volts which is suitable.

I have this circuit up and running right now and it works perfectly fine. Only problem is that it requires two 12 volt sources. If i try to use a single 12 volt source to power both circuits nothing works, and thats is my problem.

Do you think it may have to do with the crappy voltage divider i used? BTW, any solution is appreciated. I only decided to use these methods because this is the knowledge i have learnt so far in university.

9. ### kubeek Expert

Sep 20, 2005
5,452
1,036
It would be much better if you said what goes in and what comes out. You said that you want really low frequencies to go in, but frankly I have no idea what is your idea of the output. If you can clearly define what the leds should do based on the input then I am pretty sure you will get your answers.

10. ### shaheenster Thread Starter New Member

Mar 13, 2014
6
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I want the LEDs to light up to the tempo of my music's bass coming from my audio jack.

So in the schematic I posted, I gave a simple scenario where the music is giving out a constant bass note at 1 Hz. So the output should be a constant voltage to turn the LED's on.

Tell me if that helped or if u need me to clarify anything else.

11. ### GRNDPNDR Well-Known Member

Mar 1, 2012
519
15
LEDs generally don't run on 12V, they are usually 1.5 - 3 VDC, It's the resistors that determine the voltage.

12. ### shaheenster Thread Starter New Member

Mar 13, 2014
6
0
yep, its just that ive got an led strip here catching dust and id like to use it. I think it was originally meant to be attached to a car so its rated for 12 volts