Opamp setup doubt

Marciokoko:
Yes, the circuit point is ground. I just got the 100kΩ resistors and Ill try out the circuit. FTR, Im trying my original circuit which is this one:

With a single transistor output..... it can put a lot of current into your speaker in one direction. (eg...when the input to the transistor goes high. But when the input to the transistor goes low .... to around 0V or so, it will turn off. So....while the 1 transistor circuit can generate a nice large positive voltage, it can't generate the negative voltage. For a pure signal (pure sinusoid), the voltage rises from zero to a maximum voltage, then it drops back to zero and keeps dropping down to a negative (absolute minimum voltage, or could say negative max). The single transistor circuit can't generate the negative voltage part of the cycle.

Well...... I guess it could do it..... if the DC voltages are designed in a particular way, but then you would need to use an output coupling capacitor and maybe run into RC charge/discharge issues at low frequencies ....leading to signal distortion.

So ... to get around this, they use a 'push-pull' configuration.... one transistor turns on to handle the positive voltage cycle, and then the other one takes over to handle the negative voltage cycle. No output capacitor needed........ so output is directly coupled to the transistor amplifier.

In your simulator....could rig up something like this to look at ....

[/quote]

So like polymorph said in post #58?

I ask because I dont have a 2N2907A, but I do have a 2N3906.

I do have 10 & 100uF caps but they are electrolytic.

Marciokoko:
So like polymorph said in post #58?

I ask because I dont have a 2N2907A, but I do have a 2N3906.

I do have 10 & 100uF caps but they are electrolytic.

Hi there marciokoko. Apologies..... yeah.... the transistors and cap values in my simulation were kind of just examples.... I just chose cap values that were large enoiugh to ensure that the capacitor impedances are very small for the AC signals.

If you have 2N3906, yeah....could certainly try that.

Ok so Ive wired it up! Its quite a feat just wiring it up.

Id like anyone to point out any mistakes in the wiring. The only thing Im missing is the 1Ω-1Ω bridge between Emitter and Emitter of the 2N2222 and the PNP-3906. The reason I dont have the 1Ω-1Ω bridge is that I dont have any 1Ω resistors...

Can I skip the 1 ohm resistors?

Skip as in leave them out, or short. Use a very long wire.

Ok thanks. Ill try that.

BTW, I just found this while looking for something else:

This works because the mic is not producing the voltage signal, the arduino is reading it from the SD card, therefore the signal is stronger?

It works because they are using an LM386, which is a purpose built audio amplifier, something that someone mentioned very early in this thread.

Ok I just got an LM324. I had already ordered it before I posted, because if you recall, this post was originally taken from a tutorial that did use a LM324. I still havent gotten the LM386 so Im wondering,

  1. Should I really bother trying the circuit Southpark#76 using the LM324,

  2. Or even my original circuit marciokoko#1 (which got translated to marciokoko#73)

BTW, I just noticed the LM324N is like this:

which doesnt have Vcc+ and Vcc-, but rather Vcc & GND. Would I connect the -9V to GND pin on LN324 if I did try it?

Marciokoko:
Id like anyone to point out any mistakes in the wiring.

Well, for starters, the 2N2222 has 3 leads but you've only connected wires to 2 of them. Likewise the 2 large capacitors are only connected one 1 of their 2 leads.

Maybe you should spends more time and effort to carefully compare your wiring to the schematic? One useful approach is to print the schematic and use a colored pen. For each physical wire, look at the 2 places it actually connects and draw over the wire on your schematic. If you do this, because those parts have not connection at all on some of their leads, you'll end up with parts of the schematic that aren't colored in.

Yes the 2 transistors are missing their connection because I was waiting for the 1Ω resistors, but ill use the long wire instead.

The caps I haven't wired them up because I was re-wiring everything when I realized the LM324N was different in the sense that it doesnt have a Vcc- and Vcc+. How should I wire that part up, Vcc- to GND-LM324 and Vcc+ to Vcc-LM324?

Thanks

Marciokoko:
...

The caps I haven't wired them up because I was re-wiring everything when I realized the LM324N was different in the sense that it doesnt have a Vcc- and Vcc+. How should I wire that part up, Vcc- to GND-LM324 and Vcc+ to Vcc-LM324?

Thanks

Either a negative voltage, or a ground will work. Ground is V- when it's numeric value is zero volts. Using ground will make it a "single supply" amplifier, meaning that it's range will be cut off on the bottom. Note that some data sheets call it GND, and some call it V-. Like this:

Marciokoko:
Yes the 2 transistors are missing their connection

From the length of this thread, it probably seems like you can request an unlimited amount of time & effort from the community to provide design assistance. Why bother getting things right, or even mentioning the things you know are wrong, or even go to the trouble to get a set of good photos which shows the whole build and gives multiple angles to view all parts?

because I was waiting for the 1Ω resistors, but ill use the long wire instead.

Bad idea. Maybe someone will write a lengthy explanation.

The caps I haven't wired them up because I was re-wiring everything when I realized the LM324N was different in the sense that it doesnt have a Vcc- and Vcc+. How should I wire that part up, Vcc- to GND-LM324 and Vcc+ to Vcc-LM324?

Thanks
[/quote]

Ok I connected some jumpers and got their ohms to be 1Ω. The issue Im dealing with is that because I had a split power supply set up and Im connecting the opamp's GND to vcc- on the split supply, I have some things connected to ground and others connected to vcc-.

Connected to Ground (midway between vcc- and vcc+):

mic
speaker
10uF cap on the way to v+ opamp
opamp negative feedback loop

Connected to Vcc- from split supply
GND opamp
100uF (Vo) thru 10k R
2n3906 collector

ChrisTenone, I read your reply #87 but i want to make sure I understand it right before firing this up. According to what I have, GND on opamp would be connected to -9V as well as the 100uF (Vo) thru 10k R and the 2n3906. Should I move these to real ground which will actually be 0V because it is in the middle of the 2 9V batteries?

Thanks

Marciokoko:
Ok I connected some jumpers and got their ohms to be 1Ω. The issue Im dealing with is that because I had a split power supply set up and Im connecting the opamp's GND to vcc- on the split supply, I have some things connected to ground and others connected to vcc-.

Connected to Ground (midway between vcc- and vcc+):

mic
speaker
10uF cap on the way to v+ opamp
opamp negative feedback loop

Connected to Vcc- from split supply
GND opamp
100uF (Vo) thru 10k R
2n3906 collector

ChrisTenone, I read your reply #87 but i want to make sure I understand it right before firing this up. According to what I have, GND on opamp would be connected to -9V as well as the 100uF (Vo) thru 10k R and the 2n3906. Should I move these to real ground which will actually be 0V because it is in the middle of the 2 9V batteries?

Thanks

Most opamps use a dual power supply, V+ and V-. If you make V- equal to zero volts, it is referred to as a single supply opamp. You can use the LM324 either way, you just won't get any negative voltage output with a single supply.

Right, but at this moment I still have the 2 batteries making up a split supply +9V and -9V. Thats what I mean by "I have connected to GND and some connected to Vcc-).

Im thinking I should move the:

GND opamp
100uF (Vo) thru 10k R
2n3906 collector

to real GND from the supply, 0V.

Marciokoko:
Right, but at this moment I still have the 2 batteries making up a split supply +9V and -9V. Thats what I mean by "I have connected to GND and some connected to Vcc-).

Im thinking I should move the:

GND opamp
100uF (Vo) thru 10k R
2n3906 collector

to real GND from the supply, 0V.

The two 9V batteries will be connected like this...

  • -******+ -

The starred symbols represent the connecting wire between the - terminal of battery #1 and the + terminal of battery #2.

The wire will become the '0V' side of things (itself).

  • -*******+ -

*0V

The + terminal battery #1 will be +9V.
The - terminal of battery #2 will be -9V.

The connecting wire itself will be 0V.

And, if we're working with arduino...... we also usually connect that wire (0V) to the GND pin of the arduino as well.

Southpark:
...

And, if we're working with arduino...... we also usually connect that wire (0V) to the GND pin of the arduino as well.

Totally correct. But it needs a caution!!!

Do not hook up the + or - voltages to an Arduino. Both +9 volts, or -anything can fry things in the Arduino world.

ChrisTenone:
Totally correct. But it needs a caution!!!

Do not hook up the + or - voltages to an Arduino. Both +9 volts, or -anything can fry things in the Arduino world.

Excellent word of caution Chris. Yeah.....definitely don't hook up +9 or -9 volt to the arduino digital or analog pins.

Yes I understand how the split supply works from +9v to 0V in the middle to -9V. Its just that since my original setup had opamp-Vcc- going to -9V and the new setup calls for connecting the "100uF (Vo) thru 10k R" and the "2n3906 collector" to Vcc-...

I guess what Im wondering is, should I do this then:

Basically break the connection from the opamp-Vcc- to -9V, and reconnect it to GND then, but leave everything else connected to -9V?