TL072 drop in substitutes? - Page 1
Forum section: electronics / projects

author: theleakydiode
author_rank: Regular Contributor
timestamp: May 09, 2020, 12:29:47 am
content: What are some part numbers of similar op amps I can substitute the TL072 for? I'm following a circuit I found online but don't have any TL072's in my bin, but I do have a random assortment of various other op amps pulled from stuff over the years (I've never really worked with them before).Its going to be running from a 12v single supply (max, I could drop it via a regulator) buffering an audio signal from a phone and adding a bit of gain before sending it off to the next stage.Thanks.

author: eblc1388
author_rank: Frequent Contributor
timestamp: May 09, 2020, 03:43:20 am
content: Your description of the application do not point to the possibility that input pins will be getting very near or at positive supply voltage Vdd level. Therefore, I think many 8-pin Dual Opamps would do just fine.If in doubt, post the circuit here.

author: David Hess
author_rank: Super Contributor
timestamp: May 09, 2020, 04:16:36 am
content: The TL082 is a direct replacement. The old LF353 is close also. In practice, most dual JFET input operational amplifiers will be acceptable.

author: Zero999
author_rank: Super Contributor
timestamp: May 09, 2020, 10:31:26 am
content: A schematic would help.Going by the description of the application, " buffering an audio signal from a phone and adding a bit of gain before sending it off to the next stage", it really isn't critical: the NE5532 or dare I say it, even the crappy old µA741 would probably do. The only op-amp I would stay clear of is the LM358 which has a metric ton of crossover distortion, although that can be mitigated with pull-down resistors, on the output.

author: SiliconWizard
author_rank: Super Contributor
timestamp: May 09, 2020, 02:04:01 pm
content: Yes don't fret - your application seems absolutely NOT demanding whatsoever. Even an LM358 would be fine. It's a bit crappy distortion-wise, but has still been used in a ton of low-end audio circuits.The thing to check is that the replacement can be operated at +/-6V (Vcc-Vee = 12V). You didn't exactly say what kind of phone it is, but audio from a phone is not exactly hi-fi anyway.

author: theleakydiode
author_rank: Regular Contributor
timestamp: May 09, 2020, 08:00:55 pm
content: Is this ok or have I messed it up? It just needs to give some gain from the phones headphone output without introducing new problems. The TL494 is doing PWM and works without the op amp but just needs a bit more swing to get it to go further.Quote from: SiliconWizard on May 09, 2020, 02:04:01 pmIts a Samsung smartphone, would the attached schematic be ok?Quote from: Zero999 on May 09, 2020, 10:31:26 amThanks, does my schematic look ok then?Quote from: David Hess on May 09, 2020, 04:16:36 amBingo I've found some LF353 chips in the box! I guess I'll be using that then.Quote from: eblc1388 on May 09, 2020, 03:43:20 amThanks, I've attached a schematic but am not sure if its done correctly or what problems it could cause.

author: SiliconWizard
author_rank: Super Contributor
timestamp: May 09, 2020, 09:26:54 pm
content: It's not OK if you want a gain > 1. It's a unity gain buffer.

author: theleakydiode
author_rank: Regular Contributor
timestamp: May 09, 2020, 09:30:38 pm
content: Oh, I'm not quite sure what that means. What would be the correct way to set it up for a small gain of say 5?

author: Zero999
author_rank: Super Contributor
timestamp: May 09, 2020, 09:55:51 pm
content: The LF353 is very similar to the TL072.That circuit will work, but might need improvement.What's the lowest frequency of interest? the input impedance of your circuit is R4||R3, which is 2k35, giving a lower cut-off frequency of F =1/(2pi*RC) = 1/(2pi*2350*1*10-6) = 68Hz.If you want more bass response you could increase R4 & R3 considerably. The LF353 is a FET input op-amp with very low bias currents and a huge input impedance, so much higher value resistors can be used.Consider increasing the value of C1, for more bass response.R5 doesn't do anything. The gain is unity.How smooth is the 12V rail? You might want to bypass R3 to 0V with a capacitor and connect it to the +input, via another resistor.Quote from: theleakydiode on May 09, 2020, 09:30:38 pmBy using a non-inverting amplifier circuit. The top-right hand one in the schematic below:Credit: audioguru for originally making this schematic.Gain = 1 + R1/R2

author: theleakydiode
author_rank: Regular Contributor
timestamp: May 09, 2020, 10:39:44 pm
content: Quote from: Zero999 on May 09, 2020, 09:55:51 pmThanks, so the one in the edited version of my image won't add any gain? Actually come to think of it low base response isn't really good in my circuit, its really a mid-tweeter sort of thing starting at a few khz.The 12v supply is really clean and comes from a battery or lm7812 regulator, I'll use a ferrite bead in series and decoupling caps across the op amps supply pins.What sort of resistor values would I need for the top right version?

author: james_s
author_rank: Super Contributor
timestamp: May 10, 2020, 03:40:28 am
content: Compare your circuit to the examples presented here, you have a resistor from the output to the inverting input but there is no corresponding resistor to form a voltage divider with the one that's there. Since the inputs have essentially infinite impedance, the resistor you have is doing nothing and the potential on the inverting input is going to be equal to the potential on the output, this results in a unity gain buffer.You should try to gain a fundamental understanding of how an op-amp works and how to calculate the gain, then it will be easy to figure that part out. Note the comment under those examples,Gain = 1 + R1/R2, pick a value for one of those resistors, 4.7k is a reasonable starting point, then go from there.