op amp example?

Status
Not open for further replies.
Jump to Latest
#2
Here you go. The basic inverting configuration 🙂 Do you know how it works and how to calculate the gain and input impedance ?

The opamp can be any general purpose type.
 

Attachments

  • Capture.PNG
    Capture.PNG
    138.2 KB · Views: 281
  • Capture2.PNG
    Capture2.PNG
    145.5 KB · Views: 266
#6
Sounduser said:
I don't know much to be honest. I was reading about ti audio op amps. Sounds interesting.
Click to expand...

Opamps are really useful building blocks and you can have a lot of fun understanding how they work. Full blown text books can be a little off-putting with all the maths and yet the basics are really simple.

The opamp used with feedback (so any circuit you will come across in audio) always tries to maintain the difference between the two input terminals at zero.

So in that little example, if we apply plus 1 volt to the input, then the output has to "rise" to minus 10 volts to keep that difference to zero. 1 volt applied to the 1k input resistor needs minus 10 volts applied to the other end of the 10k feedback resistor to maintain that balance. So the gain is Rfb/Rin but remember its a minus value which in practice means its inverting of phase. Do you see how the waveforms are 180 degrees out of phase.

The input impedance is simply the value of Rin.
 
#8
One problem with typical op amps is you will still require voltage gain after the IC because of the limited supply voltage and output swing from the op amp. Output stages are generally current gain only. You could find a higher voltage op amp or limit your supply voltage to +/- 15 volts. Several things you could do to work around, such as add a voltage gain stage. You still have to deal with bias. Why not use one of the high performance IC drivers? No voltage regulation for the op amp to worry about and it handles everything including protection of the output devices.

Edit: I'm assuming OP wants discrete after the op amp.
 
Last edited:
#9
in general i would not use an inverting configured op amp as the first stage because in that configuration all the stuff before that stage becomes part of the feedback loop. that's the reason that most buffered inverting gainclone (BIGC) designs use a non-inverting buffer in front of the inverting configured chipamp. example here http://www.diyaudio.com/forums/atta...ed-buffered-inverted-gc-carlos-filipe-igc.gif BTW, the design at this link could be improved by replacing the 78/79 series regulators with a circuit based om LM317 and LM337 -- much quieter.
 
Last edited:
#11
sfthurber said:
....................., the design at this link could be improved by replacing the 78/79 series regulators with a circuit based om LM317 and LM337 -- much quieter.
Click to expand...
It's my reading of the reports I have seen that the 317 and the fixed voltage regulators perform very similarly.

It's only when the voltage setting resistor from adjust to Zero Volts has a noise attenuating capacitor attached that the 317 manages to outperform the 78xx regs.
 
#12
AndrewT said:
It's my reading of the reports I have seen that the 317 and the fixed voltage regulators perform very similarly.

It's only when the voltage setting resistor from adjust to Zero Volts has a noise attenuating capacitor attached that the 317 manages to outperform the 78xx regs.
Click to expand...

to flesh out my earlier post:
the design at this link could be improved by replacing the 78/79 series regulators with a well-designed circuit based on LM317 and LM337 -- much quieter
see,e.g.
http://diyaudioprojects.com/Technical/Voltage-Regulator/Voltage-Regulator-Schematic-Protection-Diodes.png
 
#13
Many Fender guitar amps are made out of an Op Amp driving a few Darlington power transistors (TIP142/147).

Some use a floating +/-20V rails Op Amp to handle +/-40V rails (the Op amp only cares about voltage difference between +V and -V pins, not absolute value) , others ground the speaker out rail and consider the ungrounded filter caps midpoint as speaker +

FWIW QSC amps use standard Op Amps to drive +/- 80 V rail big Rack Amps, using the same "grounded output" trick.

An externally hosted image should be here but it was not working when we last tested it.


See that the driving Op Amp runs on +/-15V and the outputs use +/-54V in this one.

Also that collectors are grounded (I couldn't believe when I repaired then first one and saw transistors mounted to grounded heatsinks, with grease but without micas !!!!!!)
and speaker hot is the middle of the 3300uF filter caps ... which of course are ungrounded.

EDIT : I post this practically unreadable scan under the fair use convention, for didactic purposes.

Very much doubt anybody can clone one using this.
 
Last edited:
Status
Not open for further replies.
Top Bottom