So I’ve been trying to make a VCO with the AS/CEM3340, and after two AS chips and one CEM chip, I’m no closer to getting the design off the breadboard. I’m still new to electronics, but I’m baffled as to why it won’t work. I’m sure I haven’t burnt any of the chips out, but on all three of the 3340 chips the 3340 VCO Core that LMNC released isn’t working. Can anyone see the problem here? Excuse my excessive amount of trimpots, I’m just using them in place of resistor values I don’t have. That should be fine right?
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I think you need to provide a bit more details than “isn’t working” because that can mean anything 
Have you checked the voltages?
This guide is about the performance oscillator, but a lot applies to any build:
This search has more.
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Hi, I’m not getting any signal from any of the three outputs. I have checked the voltages and they’re all within operating ranges of the datasheets. I’ve checked all the levels etc of everything the oscillator is plugged in to and it’s all fine, so I believe the issue is on the breadboard. I’ll have a look through them threads at some point, but if you know of any common problems like mine please let me know.
Measured signal (e.g. using an oscilloscope) or by listening for it? If CV is outside bounds, you won’t hear the output, but it’ll probably show up on an oscilloscope.
See the annotated link for where to measure CV and supply voltages in circuit. Note that this is a bit different from what you’ll find in the datasheet, since the latter doesn’t necessarily tell you what voltages you’ll see in the design you built (e.g. the CV input pin is current-driven, and held near 0 V by the 3340, and the datasheet generally gives you values for ±15 V supplies, not ±12 V).
Couldn’t hear anything. I don’t have a proper oscilloscope but I’ll run the signal into my audio interface and into an oscilloscope VST now. I’m getting all the right sort of voltages. Good to know about the CV pin not giving voltages as I did get nearly 0V when I tested the voltage there. Was going crazy trying to figure out if there was something wrong with the pot or 100K resistor.
So it looks like one of my AS chips is bust, as is my CEM one. Luckily one of my AS3340’s seems to work, although I’m currently having a problem with the coarse tune. As soon as I put a pot into the circuit (wiper to pin 15 via a 100K, and one of the side pins to +12V) I lose all signal. I measured the point the annotated stripboard layout mentions and it looks fine, but measuring voltage at pin 15 comes back with -0.08V with nothing connected to it, and then 0V when any voltage goes to it (via a pot or a resistor). Not sure why this is happening…
Pin 15 (CV) is a summing node and is held near 0 V by the 3340. To measure the CV, measure the voltages on the other side of the summing resistors, and add them together. See the “measure CV here” annotation in the drawing, and comment #3 in that thread. You need around 6 V to get an audible frequency.
The third pin should connect to ground. Specifically the one on the left if you’re looking at the front of the pot with the pins pointing down. +12 V is on the pin on the right. Then if you turn the knob fully counterclockwise you should have 0 V on the center pin, and you should get the same signal out as if the pot is not connected.
s/should/can be/. Grounding is optional, and Sam’s layout leaves it unconnected (you get a slightly wider tuning range with it grounded, see the drawing).
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I tried connecting the pot’s other pin to ground and got somewhere. It basically went from a high mid frequency with the pot fully down, up to ultrasonic in a tiny turn of the pot. Tried swapping for a 10K pot instead and it didn’t help, but it should just work with a 100K pot and 100k resistor right? I’m not sure what’s going on. I’ll have another go at it tomorrow or Sunday. Any suggestions for then?
With that pin grounded the tuning range for that pot is 12 octaves (0 to 12 volts), so it wouldn’t take much turning to get up to very high pitch if you’re starting from “high mid frequency”. But if that pot is the only CV source it should start below audible frequency. As @fredrik says you need 6 V for an audible frequency. So either this 3340 is defective too, or you have some other voltage source connected via a resistor to pin 15 in addition to the tuning pot.
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Hi again, been a while. I’m just working on the oscillator now and with 0V going into pin 15 I’m getting about 93Hz, but it goes out of human hearing range at around 0.14V. The only other thing connected to pin 15 is a 470R resistor which goes into a 10nF capacitor to ground. Any ideas on how to fix this?
I keep repeating myself, but pin 15 is a summing node and is held near 0 V by the 3340. To see what CV you have, you need to measure the voltages on the other side of the 100k resistors, and add them together yourself. See the drawing I keep linking to.
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Sorry, I should have mentioned that I was measuring before the 100K resistor as you suggest. The curve is just that sharp!