I added an buffering opamp on the output. Now, the output load doesn’t affect and modify anymore the signal frequency.
The core oscillator is unchanged:
It’s the classic 2 op amp configuration. The first part (U1A, R1..R4, C1, C2) is an integrator circuit. The second part (U1B, R5..R8) is a schmitt trigger comparator.
U1A output produces the alternating “ramp” signal, giving us the “triangle” signal while U1B output is a square wave signal, 90° phase shifted.
The frequency range is selected by switch (or jumper) S1.
Here’s the new output stage:
U1C is a non inverting amplifier. The optional potentiometer R9 allows you to adjust (reduce) the output signal. The amplification gain is A = 1 + (R10 / R11).
The LED driver is different. Now it’s an op amp instead of a transistor:
The PCB is 5×5 cm wide.
Here are some pictures showing a double eurorack LFO:
I made two panels with FPE: