Go Down

Topic: Opamp setup doubt (Read 1 time) previous topic - next topic


Again - you can't drive a speaker with that unless all you are trying to do is get a "buzz" output. In which case, you could skip all that fuss and just use the 2N2222.

That circuit will only source current, it cannot sink current.

Also, the way it is wired in your schematic puts nearly 9V across the speaker. I have no idea what your description of moving the 5k resistor means.
Steve Greenfield AE7HD
Drawing Schematics: tinyurl.com/23mo9pf - tinyurl.com/o97ysyx - tinyurl.com/q7uqnvn
Multitasking: forum.arduino.cc/index.php?topic=223286.0
gammon.com.au/blink - gammon.com.au/serial - gammon.com.au/interrupts


Jul 20, 2016, 12:21 am Last Edit: Jul 20, 2016, 12:24 am by Southpark
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 ....



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.


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.


Jul 23, 2016, 02:25 am Last Edit: Jul 23, 2016, 02:26 am by Marciokoko Reason: image
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.
<reminder to come up with a revealing yet clever tagline>


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?

Go Up

Please enter a valid email to subscribe

Confirm your email address

We need to confirm your email address.
To complete the subscription, please click the link in the email we just sent you.

Thank you for subscribing!

via Egeo 16
Torino, 10131