single supply alternative to TL082 op-amp

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Hi All,

I'm thinking of using this circuit to supply audio signal to arduino nano. purpose is to run an arduino based vu meter. arduino only accepts DC 0-5v. Below circuit amplify weak input audio signal & let the audio signal move between DC 0-5V. My problem is, I dont have a dual power supply or batteries to drive this thing. Is it possible to do the same thing using a single power supply ?(preferbaly 5V instead of dual 9V )

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AD8656 is a high performing 5V true rail-to-rail dual opamp, good noise and distortion, high output current. Note 6V is the absolute maximum supply for this chip. Its SMT only so an SOIC8 adaptor breakout board might be needed.

Don't be tempted by the LM358, it doesn't have the full-swing bandwidth for audio, nor is it truly rail-to-rail. It would be fine to generate a virtual ground at 2.5V of course.
 
Yes, that DC-blocking cap is in the wrong place, must come after RV2.


There are also active variable gain circuits using the potentiometer as part of the feedback network.


R15 is 1.5k for some reason? 100 ohms is standard, it protects the opamp from oscillation when driving a capacitive load like a length of cable.
 
Appreciate All the help I received.
I would also like to connect audio out to 3.3v micro controller (ex:esp8266,esp32)
So I read about op-amp usage.
Now my understanding is,If I supply 3.3V as supply voltage instead of 5V , I would be getting a signal that moves between 0 & +3.3V.
Correct me if I'm wrong. Thanks!
 
Appreciate All the help I received.
I would also like to connect audio out to 3.3v micro controller (ex:esp8266,esp32)
So I read about op-amp usage.
Now my understanding is,If I supply 3.3V as supply voltage instead of 5V , I would be getting a signal that moves between 0 & +3.3V.
Correct me if I'm wrong. Thanks!


Well if you choose an opamp that works with that low a supply, some don't. The AD8656 I mentioned above will work down to 2.7V single supply, but there will be cheaper ones. Don't go for micropower opamps though, they don't have much full-swing bandwidth.


Of course if the audio voltage is large you'll need to arrange enough attenuation before the opamp, so it fits into the available swing.
 
Hi All,

I tried the circuit with your recommendations & it worked fine
But I'm having problem connecting it my music player.(yamaha mcr-b142)
I was planning to use player earphone out to get audio signal.(connecting wires to 3.5mm female jack to get audio signal)
But, when I open the player it had this strange setup. where it ouputs audio, only when the 3.5mm male jack is inserted.(It has a switch mechanisum inside 3.5mm female jack to activate this feature )I didnt want this, as inserting a 3.5 earphone will cutdown sound from speakers.
So now I want to get audio output from speaker outputs & it has class D fully bridged output amplifier. (yamaha YDA164C-QZ with differential outputs)so how can I get this to work?
Will following below circuit helps me?
Please assist me, as I worked countless hours to reach thus far.
Thanks.


raq-issue-145-fig-01.png
 
Do you have access to the audio signal pre-YDA164 by any chance? The signal out of a Class D amp is full of ultrasonic crap even after output filtering and would require a setup with good CMRR up to rather high frequencies, a gain of maybe -20 dB, and preferably some high-frequency filtering in both common and differential mode.

Given the limited fidelity requirements for a VU meter, I'd suggest this kind of rustic circuit:
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Should have good CMRR provided resistors and caps are well-matched, and I doubt the application is going to care very much about -3 dB @ 19 kHz (-1 dB @ 9.5 kHz) - you can always use 4n7s instead. It's not the last word in noise either, but then again neither are run of the mill Class D audio amp ICs (and the application does not require extreme dynamic range anyway).

If you should find that you need more attenuation, increase R7/R10 to 20k (22k) instead.

Take note that at least R4 must be referred to Vs/2 in single supply operation.
 

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Do you have access to the audio signal pre-YDA164 by any chance? The signal out of a Class D amp is full of ultrasonic crap even after output filtering and would require a setup with good CMRR up to rather high frequencies, a gain of maybe -20 dB, and preferably some high-frequency filtering in both common and differential mode.

Given the limited fidelity requirements for a VU meter, I'd suggest this kind of rustic circuit:
773111d1565115082-single-supply-alternative-tl082-op-amp-bal2se-rustic-png

Should have good CMRR provided resistors and caps are well-matched, and I doubt the application is going to care very much about -3 dB @ 19 kHz (-1 dB @ 9.5 kHz) - you can always use 4n7s instead. It's not the last word in noise either, but then again neither are run of the mill Class D audio amp ICs (and the application does not require extreme dynamic range anyway).

If you should find that you need more attenuation, increase R7/R10 to 20k (22k) instead.

Take note that at least R4 must be referred to Vs/2 in single supply operation.

Many thanks for the reply

I'm planning to use this setup.
I'll be adding caps (0.1uf film cap) between input resistor & input to remove any dc voltage.
I'll be using mcp602 rail to rail opamp for this task.
Planned circuit will look like this excluding input caps.
let me know your thoughts regarding this setup?
Thanks

Circuit-Diagram-for-Instrumentation-Amplifier-Circuit-using-Op-Amp.png
 
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