Hey, everybody ;
Now I’m sure I’m stupid!!!
I built my VCO with the AS3340 a while ago (with a circuit almost identical to Sam’s)…
The other day I inadvertently powered it upside down because I don’t have a great way to connect my modules and without paying attention I connected it by inverting the +12v and -12v.I quickly unplugged it but of course it doesn’t work anymore!..
Would there be a way to test the as3340 without the rest of the circuit to know if it’s him or another component that has to burn? And the TL072?
Do you have an oscilloscope? If not, the quickest way is to use the once working circuit you already have, and start by replacing the TL072. If things still don’t work, odds are you damaged the AS3340.
(also, see here for some ways to protect your modules – e.g. diodes from rails to ground are easy to add, and provides good protection, at least if you have a reasonably good power supply that can handle a brief short.)
Ok so I just replaced the tl072 and it doesn’t change much…
Yes I have an oscilloscope that I use to see what it gives me for the different wave outputs.
For the moment I have a wave that looks like PWM but with a sawtooth output (which seems rather strange to me).
it’s oscillating but every 3 or 4 seconds does it come from the AS3340 or something else that burned out?
Can I test the AS3340 alone or not?
Knowing that it’s not from TL072…
Well, to test the 3340 you basically have to wire it up as an oscillator, which you have done already Are you seeing the correct waveforms but at 1/3 Hz or so? That could be that you’ve lost all CV inputs (or as likely, fried the summing amplifier in the 3340).
You can check this by measuring the voltages before the 100k resistors that are connected to pin 15; e.g. for the stripboard layout you can measure the voltages at either point A or B in the drawing here:
You want at least a few volts in total to get an audible signal; for something like 440 Hz you need just over 9 V or so (see here).
I feel you bro. When I made a AS3340 oscillator. Accidentally put a AS3310(ADSR) IC instead of a AS3340(VCO). I didn’t check the number on the main IC before testing. The Smoke was magical. Here was the fate of my AS3310 https://www.instagram.com/p/B8KDw9dBp94/ Gotta burn some too get some.
Well, then that gives me that:
-for the triangle wave output I have a square of 1/2 Hz frequency.
-For the “sawtooth” wave output I have a positive and negative peak every 2 seconds.
-For the square wave output I have nothing at all unless I set my pulse width potentiometer to a value of about 21.5k ohm, then it alternates a nice square wave for 2 seconds and then two seconds nothing…
-Between pin 15 and points A or B I have 0v. So that’s where the problem is…
Should I check the value of my capacitors and resistors?
Just to clarify, you should measure the voltages on the other side of the 100k resistors, seen from pin 15 (the points marked (v)), against ground. Pin 15 will always be near 0 V.
(measuring the voltages across the 100k resistors would also work, at least if the 3340 is working.)
If you have 0 V at the (v) points you need to check your tuning circuit.
But if your circuit worked before the reversal, I strongly doubt you fried a resistor or capacitor but not the 3340. It has more moving parts than anything else in this circuit.
On the upside, if you buy another one and it turns out that it wasn’t the 3340 after all, you can build one more oscillator (you can never have too many oscillators, etc).
Wait, 0 V from the tuning potentiometer too? You’d need a bit over 3.3 V to hit midi note 0 and about 5 V to hit the lowest note on a piano, so if you don’t get any voltage from the tuning pot at all, your keyboard may have trouble getting something useful out of the oscillator. Double-check how the tuning pot(s) are wired up.
But this could just be that the 3340 is fried; if the summing node is completely dead and your tuning pot is wired up in series with the 100k instead of as a voltage divider (see here for some discussion of various way to wire it), the current has nowhere to go.
Are you seeing the correct waveforms but at 1/3 Hz or so? That could be that you’ve lost all CV inputs (or as likely, fried the summing amplifier in the 3340).
the little I.C. grave was great , though maybe a a bit sad to r.i.p.
!