I was messing with the trimmer pots and I was able to hear a very faint ringing (I don’t quite know how that happened), so I decided to boost the volume on my speaker and boom there was some output. I now have a very quiet “square” wave (I put that in quotes because it doesn’t sound entirely square?) where volume goes saw > tri >>> sqr. The pulse width also has no effect on the square waveform.
if it goes a little, but very badly, it could not come from a bad solder somewhere ?
The square wave output volume is still low as all get out compared to triangle and saw. I have reflowed and double checked all my connections, replaced the 47k resistor (just because why not), and took out the 10M resistor between pins 4 & 5 of the AS3340. I don’t understand how there is any issue considering the schematic path for the square output is very simple.
Does anyone have any ideas or an idea of what type of reading I should be seeing?
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Hmmm. Perhaps it sounds low because the pulse width is near 0% or 100%?
-Edit- sorry, i think this was already asked. I still think this might be possible. Can you record the output in any way, or show the output in an oscilloscope? I should be able to work with a recording though.
Yes, I can record it (though I don’t have an oscilloscope unfortunately). Also, seeing that I’ve done all I can on the square wave side of things, I think you are right Caustic and it’s an issue with the PW. I have tried sweeping the PW with no effect. I’ll keep looking into that.
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There might me something not properly grounded. If it doesnt have that reference right, it might just act haywire.
A scope probe would really help here unfortunately.
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A couple things I can think of to try:
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Measure the voltage on 3340 pin 5. That’s the pulse width control voltage and it should change when you move the PW knob. What value(s) do you see?
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Do you have an audio probe? You could use that to try checking the signal at 3340 pin 4 and comparing the level there to TL072 pins 1 and 3, it should be the same in all three places. If it’s louder on 3340 pin 4 and TL072 pin 3 then there’s a problem at the op amp.
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For comparison, I have the square wave output here first and then plug in the triangle wave.
(Mind your ears)
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That’s super interesting - I knew it didn’t sound square!
Whats more, the fundamental is between 510 - 514 HZ
My first knee jerk reaction listening was mains hum, but this is a few cents lower than C5. Additionally, its pitch is identical to the TRI wave, so its clearly affected by the chip’s main pitch.
Well… that’s interesting and definitely seems to be an issue. I read 10.67 volts at pin 5 and adjusted PW and PWM with no change. I don’t have an audio probe unfortunately.
Okay, that’s interesting. I’m not quite experienced enough to know how to apply that information into troubleshooting just yet though 
. What would you suggest?
After taking a look at the wiring of the PW and PWM side of things, I couldn’t find any issues. I went back through again and desoldered everything in that area and then resoldered (I got higher quality solder since I initially made the board) and the square wave now WORKS! Thank you to everyone that helped and sorry that you guys put in so much effort for such a small error.
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But you do! You have an amplifier and a loudspeaker, according to the video. All you need is some wire and a capacitor…
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Glad it works, most errors can be distilled into one small error.
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I built a second VCO with a slightly updated and more efficient layout, however, I am getting no outputs at all with only static coming from my square wave. Anyone have any ideas for where the problem could be?
Nope. Not without knowing your circuit diagram and stripboard layout and without pictures of the stripboard.
