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Building Look Mum No Computers 3340 Simple VCO
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author Building Look Mum No Computers 3340 Simple VCO
zarar
Hi!

I find Sam very inspiring and thought I'd give the CEM3340 simple VCO build a try as I had most of the stuff laying around.

After a couple of hours of soldering where I checked all the resistors with a multimeter before placing and checking the power connectors to ensure there's no shorts i figured I'd give it a try using a powersupply from a Dreadbox Hades DIY i had around.

Plugged in some headphones in the Square output jack and plugged the power in... nothing, just a very very slight static hum.

As I'm quite new to the DIY scene, I've been trying to troubleshoot the circuit, checking connections from the IC pins to power etc, measuring up the total resistance here and there.

My question, how would you go about troubleshooting this circuit? Anyone else that has built it?

Also, what's the possibility of that i've fried the CEM3340 chip? No funny smells or smoke has been present. I had to push quite hard to fit it in the socket though.

Here's a link to the build instructions:

https://www.lookmumnocomputer.com/projects/#/cem-3340-diy-simple/

And a big shoutout to Sam for an inspiring channel!
CLee
I would have to check the data sheet but it’s very likely that you can’t drive headphones from the Square Wave output. The schematic buffers the Tri out so attach your phones there. Depending on their impeadance you may not get much of a signal there either, but you could at least confirm it’s alive. And you won’t fry an expensive chip.

I understand his goal is a minimal circuit, but you should put bypass caps on all the power pins (100n ceramic right near the power pin of the IC between the pin and ground) and maybe electrolytic (around 47ufd) at power entry to the module.
zarar
CLee wrote:
I would have to check the data sheet but it’s very likely that you can’t drive headphones from the Square Wave output. The schematic buffers the Tri out so attach your phones there. Depending on their impeadance you may not get much of a signal there either, but you could at least confirm it’s alive. And you won’t fry an expensive chip.

I understand his goal is a minimal circuit, but you should put bypass caps on all the power pins (100n ceramic right near the power pin of the IC between the pin and ground) and maybe electrolytic (around 47ufd) at power entry to the module.


Thanks for the input! Bypass caps would be there to reduce noise and spikes, right?

Also, you say the schematic buffers the triangle out, doesn't it also buffer the square output? From pin 2 on the TL072.

CLee
That's the Sawtooth out on Pin 8, is that what you were measuring?

In any case, if you're attaching headphones, attach them to a 20 cent op amp not a $15 chip :-)
zarar
CLee wrote:
That's the Sawtooth out on Pin 8, is that what you were measuring?

In any case, if you're attaching headphones, attach them to a 20 cent op amp not a $15 chip :-)


Sawtooth out, my bad. But am i wrong in thinking the sawtooth out is buffered through the TL072 as well?

LMNC Stripboard Layout
CLee
Yes, It's buffered
l3v3l6
I haven't built this particular circuit, but I've created a working one using the reference schematic in the datasheet (using the AS3340). This is very similar to Sam's circuit.

The best troubleshooting tool is an ocilloscope. I use that to determine if I'm getting any meaningful output before sending to an audio device.

In my circuit I used +15 and -5 voltages. For testing CV input I tapped a pot into the +15 supply and sent it to one of the CV inputs. To get the pulse wave you need to supply voltage to pin 5. For testing I used another pot to supply this pin. I sent output directly unbuffered to a small mixer with the output going to a audio monitor speaker. I will be adding buffering to my circuit this weekend.
l3v3l6
Quote:
Also, what's the possibility of that i've fried the CEM3340 chip? No funny smells or smoke has been present. I had to push quite hard to fit it in the socket though.



You're probably okay. I put my chip through some horrible abuse when working on my circuit. I had a +15 supply hooked up incorectly and the chip was getting too hot to touch. It survived.
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