Dual OpAmp - NJM2068D (DIP8)  - Page 1
Forum section: electronics / beginners

author: kidchemical
author_rank: Newbie
timestamp: February 10, 2020, 09:36:55 am
content: Hello EEVblog community!I am VERY new to electronics and circuits and am motivated to understand developing synthesizers.I have followed many tutorials that i could find, and followed several diagrams but am quite lost on my own.I have this Dual Op Amp "NJM2068D" that I am trying to use as a basic audio amplifier for an incoming signal (1/4" TS).Operating Voltage ±4V~±18Vschematics on NJM3068DDQuoteI just learned about negative voltage in circuitry for the first time, and the concept of virtual ground--but have questions...Since I am using an Arduino Uno to develop my project, would I lead my V- to GND on the board? Would my virtual ground (the point which i ground to the rest of my circuit?) be the point between the voltage divider?If this is true, when I have other devices on the circuit that use the same V+ rail (a OLED display for example), if I wanted them to use "max voltage" before I divided by two, I would connect 'from V+ to V-' rather than 'from V+ to Virtual ground', correct?After trying multiple generic OpAmps on Kicad and eventually downloading a SPICE model that worked (...why is this such an issue?) Running my circuit in a Kicad Spice simulation seems to work well as I am getting the correct voltages at all nodes...(why doesnt generic opamp work for me? would not amplify, simply passed signal. Also could NOT get any 555 timers to work in simulation...)So without removing the OpAmp from the board I am salvaging it from, I am trying to use it as is.\I am guessing that the Pink wire is V- while Red is V+? I hear nothing when wiring, and I assume its due to insufficient voltage, seeing as I would max at ±2.5V(not really sure what to do with the Yellow (A+ IN) either).How do I power my OpAmp (requires ±4V, so I need 9v) while still using my Arduino? I have a 12v DC power supply and the jack that fits it from another board, how can I incorporate that?The red and blue dashed wires are the 1/4" TRS and the white and green dashed wires head to a variable potentiometer which control the volume.With all the capacitors and resistors, do you think that the power rail splitting is already done for me on this board? I believe it was likely done on the mother board this connected to via ribbon but am very unsure....Without a voltage meter or oscilloscope, I am taking shots in the dark. I am really fascinated with everything I am learning quickly, but feel I would benefit hanging around a few gurus.Thank you for your time and i apologize for a million questions!

author: magic
author_rank: Super Contributor
timestamp: February 10, 2020, 10:29:24 am
content: It would help if you posted a schematic of the exact circuit you try to use / simulate.Check out the "CMoy pocket amplifier" project, it's the simplest single-opamp amplifier you can get. It will run from a single 12V supply.https://tangentsoft.net/audio/cmoy/Not sure what Arduino has to do with anything? If it's just for signal generation, it could run from a 5V supply derived from the 12V PSU. The signal would be AC coupled to the virtual ground of the CMoy.

author: rstofer
author_rank: Super Contributor
timestamp: February 10, 2020, 06:57:53 pm
content: I would find an op amp that was suitable for single supply low voltage operation with rail-to-rail input and output. Maybe the TLV2472http://www.ti.com/lit/ds/symlink/tlv2472.pdfNow the power supply is 5V and the output should be compatible with the Arduino ADCsYou need to establish a virtual ground at 2.5V with two equal divider resistors and you need to AC couple your signal (feed it through a fairly large series capacitor).Google for 'single supply op amp audio amplifier'Here's a circuit but you should omit the output capacitor if you are going into an ADChttps://electronics.stackexchange.com/questions/153911/single-supply-op-amp-audio-amplifierThis is a common project, there should be details all over the Internet.

author: kidchemical
author_rank: Newbie
timestamp: February 10, 2020, 08:48:20 pm
content: @magicI will likely be creating the circuit following the Kicad schematic I provided to test my njm2068d (as it works correctly in simulation, using AD8009 model, only one that worked for me).I would recreate and simulate the circuit of the board I am trying to follow in Kicad and debug from there, but am unsure how to create, manage, or use 'modeling and libraries' correctly to use it confidently.I am having trouble getting things such as "generic op amp" and common IC's such as "NE555" to simulate correctly 'out of the box' (am I doing something wrong here?).getting the opamp model to work in my schematic was a nightmare of brute forcing different online sources.Perhaps this deserves it's own Kicad topic...The arduino is my workbench platform that is currently powering all my trinkets. I currently using it as a tone generator / simple oscillator, learning to add harmonic filters, sequencers, etc.I plan on staying in this scope for as long as possible until I feel proficient in devising my own complete circuits.If my arduino runs and outputs 5v, I am assuming the wave generated has a 5v 'amplitude' (0v/+5v). Now in the modular world, if I am correct, range is typically -5v/+5v. I am assuming this can be achieved with an AC coupling and OpAmp signal amp?Or is the OpAmp only capable of amplifying a signal voltage to its inputted power voltage? Would I need a 10v source in this instance?As for the Cmoy pocket amp, I may actually give that a shot for experience sake! Seems beneficial.@rstoferI knew someone was going to say this, and for well reasons. I realize I am working with outdated technology, but really am interested with understandinghow things were achievedin this instance.But at the end of the day, I am going to take this advice so that I am up to par with the modernized implementations.Ordered and on the way.

author: magic
author_rank: Super Contributor
timestamp: February 10, 2020, 09:31:44 pm
content: I just noticed the schematic. This is already almost a CMoy, but it would benefit from addition of those power supply electrolytics and 100nF from V+ to V- close to the opamp.

author: rstofer
author_rank: Super Contributor
timestamp: February 10, 2020, 10:26:21 pm
content: Quote from: kidchemical on February 10, 2020, 08:48:20 pmThis is a great reference book on Op Amps - you may find Chapter 4 re: Single Supply Op Amps helpful. Do remember, "rail-to-rail" is a marketing term, not an engineering reality. Stay away from the rails by some amount, usually specified in the datasheet and, in the case of the TLV2472, you need to stay 0.2V away from the rails on output (adjust the gain to accomplish this) but the input can swing between 0V and Vdd.https://web.mit.edu/6.101/www/reference/op_amps_everyone.pdfhttp://www.ti.com/lit/ds/symlink/tlv2472.pdf