Schematic Question

Discussion in 'General Electronics Chat' started by Tony Elliott, May 11, 2015.

Hi there, I have tried to make this circuit but I can't get it to work. Can anyone explain where the

Poll closed May 18, 2015.
  1. The ground is.....

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  2. The live is.......

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  1. Tony Elliott

    Thread Starter Member

    May 8, 2015
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  2. doozer

    New Member

    May 11, 2015
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    Yes. They're not shown as they're the op amp power supply positive and negative rails. Imagine that there is a +v and -v connected to each op amp in the schematic. Use the data sheet for the op amp you are using to work out which pins these are. As there are 4x op amps in the package there will be one pair for all of them as 2 pins on the device.
     
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  3. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
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    you need a plus and minus supply with centre ground.
     
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  4. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Also, R2, R4, R7 and IC1D-12 are all common to, well, the common where the +v and -v join. You also reference your output to there.
     
  5. Tony Elliott

    Thread Starter Member

    May 8, 2015
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    http://vakits.com/sites/default/files/imagecache/product_full/LM324_0.JPG This is the op amp and I have connected to the + & - points and copied the schematic exactly. do the ground points on the audio outputs come straight from the ground rail on the op amp?
     
  6. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
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    the ground on your psu needs to go to pin 12 , the pos rail to pin 11, and the neg rail to pin 4.
     
  7. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    Ground goes to the bottom-most trace. Outputs are taken from one of the green labeled points.
    Thec ircuit needs symmetrical power supply, i.e. +15V and -15V with respect to ground.
     
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  8. Tony Elliott

    Thread Starter Member

    May 8, 2015
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    Thank you I'll research your answers tomorrow in the studio:)
     
  9. doozer

    New Member

    May 11, 2015
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    Yes but only if you use AC coupling on the outputs in this case and block DC. Audio signals have no DC offset. Add a suitable capacitor between the output and the input of your next device depending on the frequency. It will attenuate the signal at certain frequencies (reactance of cap = 1/(2*pi*f*c)) so a larger capacitor i.e. 10/100uF will block DC here fine in the audio frequency range (things get a little more complicated after a couple of MHz).

    Also don't assume those are good audio outputs - they will swing close to the supply voltage which is going to be much larger and most "line level" audio inputs are expecting consumer level outputs so they will cause massive clipping without any attenuation. See: http://en.wikipedia.org/wiki/Line_level - you should probably add an attenuator (a potentiometer - 5/10k is usually fine - in a voltage divider arrangement between the output after the coupling capacitor I mentioned above.

    You will probably be able to hear a wrong capacitor value as a muffled sounding output. Experiment with exact values if you need to. If the attenuator is set too high it will clip which sounds like a buzzing rather than a clean tone.

    Should look like this on the output (excuse my mspaint skills - it's all I've got handy):

    [​IMG]

    Don't worry about negative voltages for this. The LM324 doesn't need a negative supply. Some op amps do.
     
  10. Tony Elliott

    Thread Starter Member

    May 8, 2015
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    Thank you Doozer, I'll try that out tomorrow:)
     
  11. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    "Don't worry about negative voltages for this. The LM324 doesn't need a negative supply."

    Nope. The LM324 input stage common mode voltage range can extend slightly below the negative supply rail without introducing clipping into the output signal, but that does not mean that the chip doesn't need a negative supply any more than an LM741 (a class favorite around here) does need one. And for the TS circuit as drawn in post #1, there definitely needs to be a negative power supply voltage - negative with respect to the circuit reference potential. There are several ways to achieve this, and only one of then requires true split power supplies, but for almost any analog audio processing circuit there needs to be supply rail that is negative with respect to the circuit reference potential for the exact same reason that there needs to be a supply rail that is positive.

    ak
     
  12. upand_at_them

    Active Member

    May 15, 2010
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    Here's a similar version of the same circuit: op-amp-function-generator.jpg
     
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  13. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Better, but...

    If that is an LM324, know that the centerline of the input common mode voltage range is not the same as the centerline of the output voltage swing range. With +/-2.5V rails, a 5V rail-to-rail opamp will work much better than an LM324 if the output frequency isn't too high.

    ak
     
  14. doozer

    New Member

    May 11, 2015
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    There's no virtual ground reference in any of the stages connected to an input (osc/integrators) and this is a single supply opamp so it will still operate as intended (I know, I built this about 25 years ago). As long as the supply voltage to the opamp allows for the outputs to swing far enough based on the stage gain without going near the rails (big issue with 324s) I.e. Vicmr isn't violated as you say. Now the integrators tend to attenuate rather than amplify anyway and the first osc doesn't matter as its saturated in each cycle so this isn't likely to be an issue. Maybe if this was a wein or twin-t network with feedback through an opamp.

    Yes its not ideal but I suspect we don't really want to get into virtual grounds, split supplies and other fun things here.
     
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  15. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Not sure we're talking about the same thing. I see virtual grounds at pins 6, 9, and 13, and a floating connection to pins 3, 5, 10, and 12 that should be a true GND connection. GND being the analog circuit reference potential, not necessarily either power rail.

    ak
     
  16. Tony Elliott

    Thread Starter Member

    May 8, 2015
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  17. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Yes, but the output voltage range will be reduced. The data sheet for whatever opamp you use will list how close the output can come to the + and - supply voltages,

    ak
     
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