Troube with simple two tone buzzer

[techninja80]

Hi folks, just learning here.  Using microcap to enhance the learning process, and was working on my first ever fully designed circuit.  Trying to use as much analog as possible.  Having using a 555 timer to generate my square wave I used a rc to convert to sine.  However whenever I put it through my speaker driver circuit I get square waves again.  Would really love to get my lovely sine waves back. Sorry for the pdf but it is the format I use.  I use a e-reader in my lab when I am testing the circuits.  Please help block diagram, as well as each component is provided, as well as transient analysis that details my issue. see last analysis.

Thanks again to all you wizards.

[pcprogrammer]

Have not looked at your schematic, but is sounds like you are driving the amplifier to hard. Add a potentiometer in the audio path to lower the voltage at the input of the amplifier.

When you amplify a sine wave so much that it runs into the supply rails it will become a square wave.

[techninja80]

Thanks, I have tried this however whenever I do the waveform collapses.  I am attempted to fines the signal all the way to the amp, but the minute its there its squared out.

[fourfathom]

The main problem (and there are several) is in your "sdriver" block.  You have two saturating transistor amplifiers in series, with no way to control the gain or force them into a linear mode of operation.  The simplest fix might be to change that block to a single "emitter follower" stage.

It looks like your speaker has a 100K resistor in series?  That's not going to give you much sound.

Your op-amp seems to have a +5V / 0V power connection.  The gain-setting resistor in the feedback network is connected to ground.  Since your "sigriser" block biases the input voltage to a fairly low value, I guess the amplifier might be operating in the linear region (I haven't checked), but this isn't usual practice.

Your RC / sigriser circuit isn't much of a filter.  It works somewhat, but could be simplified and improved.  Not the source of your clipping problem though.

There's probably more, but you might start with this.

[Terry Bites]

 Its unusual to use macros unless you haven't got the actual models. Hiding stuff inside macros will make your debug life harder and it wont help conmunicate your ideas to others.

The output stage dc operating point is dependent on the applied signal. There is a lack of ac coupling and without it single supply ciruits will not function properly or at all. Not a good situation. Aim to separate the DC operating point(s) from the signal path(s). The opamp is is suffering from the same issues, DC at the input is pushing the output too near vcc-1.5, the max for a 358. Aim to get to vcc/2 at the output. Worry about transistor biasing after AC coupling first. R3 needs a cap in series to ground to kill the DC gain. Doing this lets you set the ac gain to a higher value.  In gereral you need to rescale your Rs and Cs by an order of magnitude like 10k, not 1k. Find out why 10k is the most popular value used in small signal opamp ciruits.

You'd want to use a cap to couple the amp to the to the speaker. You don't want DC flowing in the speaker. If you put an 8R speaker in your arangement you might draw 100s of mA through it. Ouch.

BTW there is a way of generating sinewaves using counters. A diy DAC. It simpler to filter too becasue the unwanted frequencies is a long way off from your fundamental. eg www.electroschematics.com/digital-sinewave-oscillator/

[techninja80]

Wow thanks alot.  Like I said, I am self thought, and am using the program to understand what is going on under the hood.  You have provided a wealth of things to research and look into, and test.  Thanks a bunch.  Hope to have some good news with a much better design.  Might pick your brain later.