In the world of tube high-fidelity audio, very few preamplifiers can claim the same legendary status as the Klimo Merlin. Manufactured in Germany with exceptional craftsmanship, this unit was designed to deliver a listening experience that goes far beyond simple signal amplification: with a declared frequency response from 3 Hz to 450 kHz, a maximum output of 25 V, and total harmonic distortion below 0.07%, it is a true technical masterpiece. The Merlin fully reflects the philosophy of its designer: allowing the tubes to express their natural character, integrated in a circuit that preserves timing, dynamics, and analog charm without compromise.

This Klimo Merlin was delivered to me in completely original condition, but affected by a noticeable hum and several signs of aging. In addition to a few capacitors that were out of specification, the real issue was the layer of dirt and old solder flux that had never been cleaned, which over time had started to attack and corrode the PCB traces. I carried out a thorough cleaning by brushing and washing the circuit using proper non oily products, suitable for removing residues without leaving conductive traces. The PCB turned out to be extremely delicate: years of acidic flux and oxidized solder likely weakened it, and even with the use of a desoldering station, removing components without lifting traces or damaging the metallizations was quite challenging.

In the picture below you can see the replacement of the 4 capacitors located in front of the 2 transistors: the original ones, in plastic housings, were no longer within tolerance. On the right, the filament supply electrolytic capacitor was also replaced because one lead was broken. All the other capacitors, especially the orange “ERO” and yellow “Frako”, were tested one by one with an RLC meter: not only did they measure perfectly, but their capacitance was equal to or even higher than the rated value, with ESR significantly lower than many modern audio-grade capacitors. When vintage components show such outstanding instrumental performance, they MUST be left in place! I highlight this because many repairers, lacking proper measuring instruments, tend to replace all electrolytic capacitors with cheap modern parts, completely ruining the original sound character of the device.

After the restoration, the unit is back to working properly. Below are the instrumental measurements.

Frequency response

RIAA section frequency response

THD