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Square-wave synth
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pq



Joined: Feb 15, 2013
Posts: 9
Location: Brazil

PostPosted: Fri Feb 15, 2013 4:58 pm    Post subject: Square-wave synth Reply with quote  Mark this post and the followings unread

Hello,
I wanted to begin making my own synth, so I decided to follow this tutorial, I bought all the components (except the DC jack, I bought a 9V battery instead, and the perfboard I bought is a bigger one) plus a switch so I could turn it on and off, however, the schematic was really confusing and I couldn't make it work. I would like to know if there are any other guides on making a simple square wave synth which can be made using the components I bought for that other one.

Thank you in advance.
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andrewF



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PostPosted: Fri Feb 15, 2013 5:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi
welcome to e-m

Probably best to try troubleshooting your circuit rather than jumping to a new one. It is pretty normal to find circuits do not work straight away, one tiny mistake can stop everything.

What part(s) of the schematic are you not sure about?

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pq



Joined: Feb 15, 2013
Posts: 9
Location: Brazil

PostPosted: Sat Feb 16, 2013 9:44 am    Post subject: Reply with quote  Mark this post and the followings unread

There are 10k resistors on the circuit which aren't on the parts list, and also three 1M resistors, so I believe there is an error (either on the parts list or the circuit). I don't understand what to do with the +4.5V and -4.5V parts.

I'm new to electronics, though, so this circuit might just be too advanced for me...
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-minus-



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PostPosted: Sat Feb 16, 2013 12:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

I think part of the problem here is the project has not been documented well and is unclear. There are much easier ways to make an oscillator. I'm not sure if you are able to source parts locally but getting hold of a 40106 IC is perhaps a better way to do this.

If you are a beginner I think it's important to get a result quickly with minimum components or you'll be turned off this electronics thing. I've attached a simple oscillator schematic. It's from the Beavis Audio site. The pot size and capacitor value are not all that important at this point. Pin 14 of the 40106 goes to +V, pin7 to ground.

It would be very worthwhile getting a small breadboard to experiment on. That way you could try different component values and see/learn what happens. Here's a link to the Beavis Audio site too:

http://www.beavisaudio.com/Projects/CMOS_Synthesizers/


EDIT
Just incase you want to have a go at trying to get what you might have built so far working.... The 9V battery + and - are connected together with two 10K resistors in series. This is creating a ground point where the two resistors join. This must be taken to all the parts on the schematic where you see those ground symbols (the three little lines). The + terminal of the battery has to go to pin 7 of your 741 op amp. The - terminal of your battery must go to pin 4. Maybe try this first and see if you can get this working.


Schematic-40106-Simple-Oscillator.png
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Schematic-40106-Simple-Oscillator.png



Last edited by -minus- on Wed Mar 20, 2013 10:16 am; edited 1 time in total
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defog



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PostPosted: Wed Mar 20, 2013 9:53 am    Post subject: Reply with quote  Mark this post and the followings unread

For that Beavis audio oscillator schematic, you'll need to add the decoupling cap to block DC voltage from hitting your speaker/amp. You don't need the other resistors after it or the volume control necessarily though:

Posted Image, might have been reduced in size. Click Image to view fullscreen.

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pq



Joined: Feb 15, 2013
Posts: 9
Location: Brazil

PostPosted: Mon Apr 22, 2013 3:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

Sorry for the late reply - I kind of forgot about this thread. Very Happy

I checked out the Beavis Audio site, and bought a breadboard. The projects are really easy and good for starting.
I didn't try making the 741 oscillator again, found out there was a thread in this same forum talking about it and I found an easier schematic if I ever want to try that, but I made a circuit using the Beavis Audio CMOS oscillator and a 4040 which was mentioned in the site. Since I didn't get my breadboard yet (I wasn't able to buy one locally), I figured out it would be clever to post it here to be sure if it could work.

Posted Image, might have been reduced in size. Click Image to view fullscreen.
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analog_backlash



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PostPosted: Mon Apr 22, 2013 5:05 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi pq.

This looks OK to me, but you should also connect the reset pin of the 4040 (pin 11) to 0V (ground) as you are not using this. The reset can be connected to one of the counter outputs to reset it (believe it or not Very Happy ) after a certain number of input pulses at pin 10. It can also be reset by an external trigger pulse. If you want to play with this, you should connect pin 11 to ground via a pull-down resistor (typically 100K). This ensures that the input is never left floating, even if you have nothing connected to it.

I'm not sure about the order of your outputs. You have 9 (divide by 2), 7 (divide by 4), 6 (divide by eight), 5 (divide by 16) then 4 (divide by 128). Perhaps the fifth one should have been 3 (divide by 32)? Also, I'm unsure what you are going to do with the switches (but there may be a perfectly good reason why you've put them there...).

Anyway, it looks like you're on the right track well done

Gary
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pq



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PostPosted: Mon Apr 22, 2013 7:27 pm    Post subject: Reply with quote  Mark this post and the followings unread

analog_backlash wrote:
This looks OK to me, but you should also connect the reset pin of the 4040 (pin 11) to 0V (ground) as you are not using this. The reset can be connected to one of the counter outputs to reset it (believe it or not Very Happy ) after a certain number of input pulses at pin 10.

Noted - and I'll experiment with the reset function once I buy the parts to get this project made.

Quote:
Perhaps the fifth one should have been 3 (divide by 32)? Also, I'm unsure what you are going to do with the switches (but there may be a perfectly good reason why you've put them there...).

That's right, I guess I should've paid more attention to the datasheet.
The schematic repeats for each of the 12 notes in the sixth octave, and the switches (keyboard) are used to activate each output. I'm not sure, but I believe that's how Cynosure made the basic organ circuit for his "C-MOnSter", which I'm basing this project on.

Thanks!
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analog_backlash



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PostPosted: Tue Apr 23, 2013 6:20 am    Post subject: Reply with quote  Mark this post and the followings unread

Ah, so you're building a top-octave generator - I understand the switches now! In that case, the reset pin probably won't be needed (but still keep it at 0V, with or without the pull-down resistor).

Gary
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pq



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PostPosted: Thu Apr 25, 2013 10:02 am    Post subject: Reply with quote  Mark this post and the followings unread

Is there any formula for determining the frequency of a 40106 oscillator? I tried 1/4.7(µF)R(Ohm) = 1046.5(hertz), but I'm not sure about that.
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analog_backlash



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PostPosted: Thu Apr 25, 2013 12:13 pm    Post subject: Reply with quote  Mark this post and the followings unread

I've seen 1/RC or 1.2/RC quoted, but by experiment it was a bit out (but usually in the right ball-park). The NatSemi datasheet (a bit attached) shows a more complicated formula, but you need an oscilloscope to tell you some of the values required Confused . If you've got a scope, you have the frequency anyway!

Gary


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Cynosure
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PostPosted: Sun Apr 28, 2013 7:46 am    Post subject: Reply with quote  Mark this post and the followings unread

4.7uF caps and a 10k resistor probably won't give you the range you want. With a topic octave divider you need to atart with a high frequency. Try 0.1uF instead.
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JovianPyx



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PostPosted: Mon May 13, 2013 10:25 am    Post subject: Reply with quote  Mark this post and the followings unread

Looking at this, I spot something that can often be a real pain in the butt.

That is a virtual ground. This is the bit of circuit you created with two 10K resistors to create an effective +4.5, ground (or zero volts) and -4.5.

This technique can work for circuits that are very simple and small and which do not require putting much current into or drawing much current out of ground. When larger and/or more demanding circuits are used, it begins to become a point of failure. One way around this is to "buffer" the virtual ground. This is done by adding a single opamp wired as a voltage follower. Feed the current "gnd" point into the opamp non-invert input and then put the opamp output to the "gnd" connection. This will allow the ground to deal with more current and will be somewhat self correcting should the ground try to drift.

That being said - my suggestion - don't use virtual grounds. You can make a nice +/- 9volt dual supply using two 9volt batteries. Such a supply is far more immune to noise propogation and floaty ground problems than a virtual ground. I know it requires another battery, but the advantage is "stability".

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pq



Joined: Feb 15, 2013
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PostPosted: Sat Jun 22, 2013 4:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

I've finished the schematic for my CMOS "organ", and tested what I could. So far, so good.
Thanks to everyone who helped me, please tell me what you think. Very Happy
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Cynosure
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PostPosted: Sat Jun 22, 2013 6:32 pm    Post subject: Reply with quote  Mark this post and the followings unread

It looks good so far, but here is one thing to consider:

The bypass caps go from pin 14 to pin 7 on the 40106 and 4016, from pin 16 to pin 8 on the 4040, and from pin 8 to pin 4 on the TL072. Think of it as a little power reserve that the chip can use when it needs a quick burst of power that the power line can't supply fast enough. It also smooths out any noise in the power line. You can remove the ones you have on the oscillator outputs.

However, depending on what you are connecting the output too, you might want to add a coupling cap on the final output after the TL072. As long as the cap is large enough then the value usually isn't too important. I usually use a 4.7uF cap and 100k resistor because I have a bunch of both, but I have used caps down to 1uF without noticing any change to the sound.

More info here:

http://electronicsclub.info/capacitance.htm#coupling
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fluxmonkey



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PostPosted: Sun Jun 23, 2013 1:04 pm    Post subject: Reply with quote  Mark this post and the followings unread

i think you'll need to add mixing resistors after each of the keys, prior to the output stage at U3A. i'm not sure what will happen to the levels when multiple keys are pressed.
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Cynosure
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PostPosted: Sun Jun 23, 2013 3:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

fluxmonkey wrote:
i think you'll need to add mixing resistors after each of the keys, prior to the output stage at U3A.

He has those in there, but the are right at the output of the 4040.

That will work, but it would be better if you could put them at the other end of the change as close to the TL072 as possible.
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pq



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PostPosted: Mon Jun 24, 2013 4:07 pm    Post subject: Reply with quote  Mark this post and the followings unread

I moved the resistors (having them after the switches does make more sense), and added the coupling capacitors after the TL072, not sure if the values are correct.
Posted Image, might have been reduced in size. Click Image to view fullscreen.

Also, when I removed the bypass caps after the oscillators, I didn't get any sound, are you sure they aren't needed?
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Cynosure
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PostPosted: Mon Jun 24, 2013 4:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

I don't understand the schematic you just posted. You are getting distortion with a 10uF coupling cap and 200k resistor? That seems odd, but maybe it is the voltage you are using. Most of my projects so far have been +/-5V. Anyway, you just need to use one of those options - the one that gives no distortion.

The cap on the output of the oscillator isn't required, but I know that the 4040 can be annoying sometimes. The cap might be acting as a buffer that is helping to clock the 4040. The 40106 oscillators can act weird if you don't buffer the output somehow because the cap to ground ends up interfering with circuits further down the line. I usually buffer them with another schmitt trigger. But if it works with the cap then I guess leave them in there Smile
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pq



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PostPosted: Thu Jun 27, 2013 8:46 am    Post subject: Reply with quote  Mark this post and the followings unread

Cynosure wrote:
I don't understand the schematic you just posted. You are getting distortion with a 10uF coupling cap and 200k resistor?

Oh, disregard that. I didn't understand how to calculate the values for RC.

Cynosure wrote:
Anyway, you just need to use one of those options - the one that gives no distortion.

What I want to do it add a rotary switch to choose between the three RC values (though a pot might work as well), as distortion can be desirable occasionally.

And on the bypass caps - I didn't try it with the TL072, that's probably why it didn't work.
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PostPosted: Thu Jun 27, 2013 10:32 am    Post subject: Reply with quote  Mark this post and the followings unread

The type of "distortion" mentioned on the link i posted is actually filtering. If the values are too low, then the coupling cap and resistor will act like a highpass filter.

If that is what you want, then just add a RC highpass filter with a pot for the resistor. You don't need the rotary switch.

If you want actual distortion, then there are plenty of schematics for that online. The most simple one is to overdrive a linear 4069 similar to what is used in the WASP synth.
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