I totally get why you have to ask that. I teach high school and have had to ask a lot of questions just like that.
I am plugged into power.
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Yep. All good there. Im sure I’ve shorted something, I just cant figure out where.
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Since you did these latest fixes, did you retry the calibration? If it’s tuned too low, I think you would only get the dot.
I have tried calibrating it since finding a few ground faults, and I can get it to display a note, but still no sound and the fine tune pot is having no effect. It’s weird to see ground continuity on pin one of the 704, right?
I would not try to measure resistance or continuity with power connected.
Pin 1 of the TL074 is supposed to connect to pin 2 and to R19, a 100K resistor to CVINPUTS. So no, it should not connect to ground. But again, check that with power off.
Pin 1 of the TL072 connects to pin 2 and to SQUAREOUT. Again, not ground.
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So here’s a dumb question I should have asked eariler, but I’ve been assuming the answer, does the board need anything plugged into the output jack to tune? I mean will it tune with no inputs or outputs plugged in? I assume it will as the 3340 just constantly outputs, right?
Well, if you’re getting nothing on the outputs, then there’s presumably nothing coming out the 3340 to tune from.
I suggest forgetting about the tuner for now and focusing on getting a signal.
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I think you should find out which parts of the circuit are working and which are not. And I agree with @analogoutput that you should concentrate on the analog side of the circuit first.
One way of tracing AC signals, if you do not have any specialised equipment like an oscilloscope, is to use an audio amplifier. It basically boils down to that you probe the circuit and listen whether you can hear a signal where you would expect one. This should work with an oscillator as all it will produce (most times) are signals in the audible range. You can step through the circuit and maybe find out where the signal gets lost or dampened more than you would expect.
So what you can try is:
1: make a probing cable that has shielding and a signal wire with a connector on one side which fits your amplifiers TAPE or CD input (stay away from PHONO et al.).
2: connect a capacitor of say 1 - 10 microFarad ( use whatever you have, the value is not that important as long as you are in the sub 50 mu-area) to the signal wire on the other end of the cable.
3: connect the wire’s shielding to your amplifier. Use e.g. a crocodile clip, alligator clip, or my favourite gold plated hand made caymen clip for that. Do not use a tube amp here, as this can be problematic/dangerous given some of their chassis may carry a voltage.
So a simple modern (transistor based) amp will do fine.
4: try the cable: hold your finger to the capacitor: your amplifier should humm. What you hear is mains humm which you as a person receive because maybe unbeknownst to you, you act as an antenna for.
Now choose a moderate volume on your amplifier.
5: hold the capacitor’s end against any point in your circuit you expect to find some audible signal.
You should hear this via your amplifier. If you want to continue to another point in your circuit to be on the safe side you can short the capacitor to make sure it is not charged. I’ve found that with a small capacitor value (a few micro Farads) this is not necessary.
6: Now systematically trace the signal to where it should go and hopefully you will find the problem.
Keep the probing cable, you will likely need it again for a future project.
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Thank you for your input. This thing is going to be super useful, for sure!
However, I am not getting any signal out of the chip. I think I had a square wave for a few seconds, but then I couldn’t get it back. If the chip (3340) is getting power, what is it looking to inorder to start producing a wave? I can’t sort that out from the schematic. Is it looking at cv in or 1v per oct for an input and then produces based on what it sees? Meaning that if it doesnt see anything on those pins, it won’t make a sound?
I’ve bitten the bullet and just ordered another pcb. I’ll probably still poke around in the meantime, but I’m starting over. Sucks.
No signal, or no audible signal? The oscillator has a very wide range.
I suppose no audio output. But I did get a sound for a few seconds on the square wave, then nothing. I’ve tried two other new 3340 chips, too.
Listen carefully, do you hear an occasional “plip” noise? If it’s tuned low enough, it won’t be a tone, but a rhythmic sound.
To understand more of the chip and how it is used, you may want to read CEM3340 VCO (Voltage Controlled Oscillator) designs. This is an interesting read because it also highlights the differences between usage in various known synthesizers.
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When you test the module, do you supply any CV signals? E.g. do you supply some voltage to the frequency in of the chip (pin 15)?
I had to step out for some work, but what range of voltage am I looking for?
Again! Thank you all for your patience. This project is making me feel real dumb.
Try some voltage between 0 and say 4 Volts. E.g. you can take a potentiometer, hook one end to the ground, the other to the positive power supply (12 Volts?), rotate the axis away from the side connected to the +side and set it to about 30% (that would give it 4 Volts).
Now use the middle point of the potentiometer as the signal you want to insert into the CV-in.
This should result in some frequency that is not too high or too low. Then listen to the outputs of the chip using the wire + capacitor and amplifier I described earlier.
Oh yes, and tell us what you hear.
TIL that is an expression, not a typo.
Just goes to show that we don’t learn only about music and electronics around here.