I re-used the same circuit as yesterday, but with slightly different settings. First of all, I replaced the op-amp by an LM358, which can handle higher voltages. Next, I halved all the R’s to 5 kΩ and doubled all the C’s to 0.2 µF. This reduces the loading of the feedback loop – it shouldn’t really affect the frequency.
To increase the output voltage, I connected the oscillator output signal to a non-inverting op-amp circuit:
In a nutshell: this circuit tries to keep Ve as close to zero as possible at all times. IOW, the op-amp will constantly adjust its output so that the tap on the Rf:Rg voltage divider tracks the Vin voltage on the “+” input pin.
Using Rf = 10 kΩ, and Rg = 470 Ω, its gain will be about 22x. The nice property of this circuit is that it has a very high input impedance, so there is virtually no current draw from the oscillator.
And sure enough, the output of this op-amp is a sine wave with many volts of output swing. Now it’s simply a matter of cranking up the supply voltages to ±13.6V and bingo, a ±10V sine wave:
Very clean. Better even than the original circuit – the 2nd harmonic is now -49 dB w.r.t. to the base frequency. That’s just 0.35% of harmonic distortion – excellent!
That second op-amp came for free, since an LM358 DIP-8 package has two of them anyway. So the first op-amp is oscillating (at about 470 Hz) and the second op-amp brings the output level to ±10V.
It’s quite a mess on the mini-breadboard I used, but who cares – that’s what prototypes are for:
One last check is needed to make sure that the LM358 is suitable. A component tester measures the effects of an unknown component in series with a 1 kΩ resistor. So in the worst case, with a simple wire as “unknown component”, the maximum current through that resistor will be ±10 mA. Luckily, according to the specs, an LM358 can supply at least 10 mA, and typically up to 20 mA on its output.
So that’s it: our Component Tester will need a ±13.6V supply, an LM358, and a few R’s and C’s. That supply voltage is not critical, as long as it’s stable – the output level could be adjusted to ±10V via a trimpot.
Welcome to the world of analog electronics!