I recently finished my first diy synth module: the AS3340 (CEM3340) VCO core module. It is working but the problem is that the TL072 gets pretty hot after a couple of minutes. I cheched for solder bridges or other mistakes but I could not find them. What else could be the problem? Or is it normal that is gets hot?
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The TL072 buffers the ramp and triangle waves, so if those outputs are good then it would seem there canât be anything too far wrong going on. But no, it shouldnât get really hot. Check that thereâs -12V on pin 4 and +12V on pin 8 of the op amp, and that thereâs no DC levels on the other pins. If you havenât done so already, disconnect power and check the power header to be sure thereâs no connection between ±12V or between either of them and ground.
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No, it is not normal they get hot. It shouldnât even get warm. But you might have damaged it while experimenting. This happend to me once and the TL074 got hot as well. What happens if you replace it? Does the replacement get hot as well?
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Unfortunately is this the only TL072 that I have. But I am going to order one.
In the mean time am I goin to test the votlages in the circuit.
Thanks!
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Thatâs too bad. Iâd recommend ordering a few, as they are not expensive and youâll likely need one or ore in the future if you continue building modules.
You might do a simple check to see whether the TL072 is broken. If you put the TL072 in a bread board power it, and it gets hot, then it is damaged. If it doesnât, try to build a simple amplifier with it following the application notes in the TLâs data sheet and see whether that works.
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Yes, the replaced one got hot too. Something else I came across is that when I touch the wires around the ic or the ic itself the pitch of the sound changes. Could this perhaps have something to do with the problem in my circuit?
Thatâs expected. Youâre full of water, which makes you an excellent radio antenna, and your body can also act as both a resistor and a capacitor.
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This is why I always try to think dry thoughts when messing with electronics.
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I rebuilded the vco on breadboard with a new tl072. But this one gets hot too (warm actually but I turn it off before it gets too hot). The as3340 stays cold. The output goes to an old pair of headphones since I do not have a speaker (but Iâm building one). My powersupply supplys just al litte over +/-12v (+/-12.3). Could one of these things be a problem?
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The oscillator output isnât designed to drive a low impedance device like a headphone or a speaker (your headphones were probably saved by you overloading the opamp; the full voltage would fry them). Cheap computer speakers is an OK first choice if you donât have better audio gear.
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Could I have damaged the as3340 too by doing this? Is there a way to test icâs (working with icâs is quite new for me). Thanks for helping me!
Not if you only put heavy load on the opamp; loading down the opampâs output wonât affect the circuitry connected to its inputs. And I donât think youâve necessarily damaged the TL072 by doing this, they can handle pretty high temperatures, and even handle an outright short (by dropping the output voltage to near zero). Thatâs not supposed to happen in this circuit, though, and not all circuits can handle shorts.
(I assume this is the Simple 1V/Oct Oscillator stripboard layout, btw, and not the performance oscillator?)
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Yes, youâre right. The 1V/oct oscillator on stripboard. Thanks for your reply.
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Can I just plug in my vco straight into a speaker? ( I have an 8ohm/0.25W and an 8ohm/20W.)
No, thatâs even worse than headphones (which are usually 32 ohm or so). Audio signals from modular synths are designed to be used with high impedance inputs (several kiloohms, often more), either dedicated output modules or good mixers/amplifiers/active speakers.
(for some mixers/amplifiers/active speakers you may need to attenuate the signal on the way there, because the raw synth signal is hot and may be too much for an input with limited headroom.).
See e.g. here:
EDIT: The module you mention in the other thead is a nice output module; the LM386 there is designed to drive low impedance devices.
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I had a question about ICâs getting warm. When I connect my VCO to the powerrail (without the outputs connected to something), the ICâs get just a little bit warmer than before I connecten them to the powerrail. (It is a small temperature difference but I can still feel it)
Is it normal that they get a little bit warmer when powered on?
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Yes, itâs normal. If they start to emit smoke, thatâs when you have a problem.
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A DIP IC has a âjunction to ambientâ thermal resistance of around 80 °C/W. This means that for every watt used by the chip itself, itâll heat up to 80 °C above room temperature. A lightly loaded TL072 uses maybe 1-2 mA per amp, so you can expect a surface temperature of 25°C+80°C/WĂ24VĂ5mA = 35 °C.
(this is very much an approximation; the actual resistance depends on a lot of factors, including the IC itself, how itâs mounted, and the PCB layout (more copper provides more cooling)).
If youâre hitting 50-60 °C, you need to start paying serious attention; odds are somethingâs wrong, but if the circuit is expected to operate at 60 °C or higher you must make sure that you or others cannot touch it by accident.
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I had a similar problem. Iâm building the same vco. I was in the middle of troubleshooting when I noticed the pitch drifting higher and fainter and then I couldnât get any sound at all. Iâve been testing the circuit with two 9 volt batteries in series. Iâd assumed the batteries were going dead. I donât actually have a multimeter so I donât what charge is actually on them. It seems the op amp continued to get really hot though. I did change out the opamp and it doesnât seem to be getting as hot with the same batteries but Iâm still not getting any sound. I am planning to get a multimeter obviously. I am planning to get more batteries too obviously, as I am reluctant to move on to a plug-in regulated power supply just yet. I donât want things going up in smoke just yet. When the batteries were fresh out of the box the vco was putting out a really fat sound though. Tracking in tune across three octaves on my division 6 mini sequencer. Does it sound like just dead batteries and a bad op amp?