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I'm trying to build this circuit- the red area is what I'm having problems with:

the red area is what im having problems whit

What is happening is that I have 4.5 volts for like a second then it drops to 3 volts which can't run the op amp.

I did get it to work for a while but then I re-built it on a bigger board and now it drops the voltage too low. what can be the culprit?

Is it the battery or is it the over all design for the circuit that handles the biasing of the voltage?

BTW: I haven't done any electronics in like 6 years so I might have missed something basic.

JRE
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johnny bandit
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  • So, measure the battery voltage and remember that op-amps need power rail connections. – Andy aka Dec 13 '20 at 15:31
  • so my battery is at 9,02 volts. By power rail connections do you mean the + - voltage inputs on my op amp. if so they are connected to + to the battery and - to signal ground – johnny bandit Dec 13 '20 at 16:25
  • And where is the battery's negative terminal connected? (A complete schematic including the battery would be helpful) – The Photon Dec 13 '20 at 16:28
  • so the negative is connected to the negative on my solder less breadboard, i can try and put a schematic together quick – johnny bandit Dec 13 '20 at 16:53
  • https://tinyurl.com/y6d9vf86 here is a schematic of my circuit but in this version where i use a "real" op amp the volt is about 1 on the + voltage input. – johnny bandit Dec 13 '20 at 17:08
  • A PP3 battery is not good at supplying much current. Do you have an idea of how much current your circuit draws? What is the voltage across the battery when the bias voltage drops? It will soon be cheaper to get yourself a mains-powered PSU of some sort than to keep buying new batteries ;) – Andrew Morton Dec 13 '20 at 17:38
  • so it is still 9 volts across the battery i also noticed that when i un plug the cable from my power supply circuit it then goes back to 4,5 volts. i kind of need it to run of a 9 volt battery if i cant do that, then i cant put it in a guitar and force my friends to always have distortion on hehe – johnny bandit Dec 13 '20 at 17:56
  • What is the part number of your op amp? – Bruce Abbott Dec 14 '20 at 00:24
  • its a lm348n i just had laying around, i think it can be driven by 4,5 volts cant seem to find it in the data sheet now so i might be wrong – johnny bandit Dec 14 '20 at 07:47
  • @johnnybandit If there is still 9 V across the battery then it could well be a poor connection to/on the breadboard. Ummm... could you tell me what the 100 μF capacitor across one resistor of the voltage divider is for? – Andrew Morton Dec 14 '20 at 14:38
  • @AndrewMorton so from what under stand its common to put a 100 μF capacitor to make the power clean/ less nosiy which is good for audio circuits i mean this is a distortion circuit but i dont want noise – johnny bandit Dec 14 '20 at 17:49
  • @johnnybandit That sort of capacitor would be across the supply rails (i.e. from the 9 V to the 0 V in this case). Where the capacitor is in the circuit in the question, it will have the effect of slowly raising the voltage at the non-inverting input from 0 V to 4.5 V. Imagine switching on the circuit when the capacitor is discharged: the voltage across it will be 0 V and it will take some time to charge up through the 10k resistor. – Andrew Morton Dec 14 '20 at 19:14
  • @johnnybandit Some more information: [What is a decoupling capacitor and how do I know if I need one?](https://electronics.stackexchange.com/q/2272/36731) and [Capacitor in series with voltage divider](https://electronics.stackexchange.com/q/435707/36731). – Andrew Morton Dec 14 '20 at 19:17
  • @AndrewMorton thx il read all that – johnny bandit Dec 14 '20 at 19:27

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