GOLDMUND - Swiss Made High-End Audio Equipment

All MIMESIS amps and preamps are built around the same amplification stage, which is a discrete operational amplifier of highest possible quality.

With a bandwidth of several megahertz, a slew rate around 1000 Volts/microsecond, ultra low distortion, perfect DC response, and a noise contribution in the single decibel range, this operational amplifier displays the highest electronic performance attainable.

But the most important quality of this stage is probably more in its specifics :

The same schematic can be used from a low noise phono stage to the driving circuit of a 300W amplifier. It can be powered by +/-35V to +/-85V. By simple adjustment of its gain, feedback, and slew rate limits, the same schematic is usable and easy to optimize for each function. Even inverting and non-inverting stages can be made using this very same amplification stage.

With a power supply around +/- 60V, the preamplifier circuits built with the GOLDMUND Amplification stage can receive and produce signals of nearly 40V RMS. The dynamic range possible allows the GOLDMUND circuitry to compete with tube designs. Thanks to the very low level of noise, this quality provides a dynamic range of unique extension even in lowest level preamplification stages.

The very low input impedance (<10 Ohms) provided by the high power (close to 3W) output stage and the high input impedance (more than 1 MOhms) allow long connections and a very wide range of utilization, including to drive low value volume and balance potentiometers, which are much better in sound than high value ones.

The input circuitry of the GOLDMUND amplification stage is potted to insure thermal stability. This technique allows also the lowest possible coloration by microphonic effect, by avoiding low level signal transistors to vibrate. The sonic result is an exceptional transparency.

No capacitor is needed in the GOLDMUND stage schematic. Only smallest values in the picofarad range are used to tune the slew rate, depending where the stage is used in the component schematic. The stage being DC coupled, no capacitors are needed between stages either. With the absence of capacitors in the signal path and the exceptional rejection of power supply capacitor noise, the GOLDMUND amplification stage is free from any capacitor sound, the most difficult coloration to avoid in conventional electronics.

A minimum quantity of resistors are used in the signal path. The 1% metal film model selected displays the lowest possible coloration. In the best GOLDMUND products (GOLDCUBE, MIMESIS 9.2, MIMESIS 22), even Vishay resistors are used in the signal path, despite their very high cost. Transistors have been selected for their minimum sonic thumbprint. More, the double inverted symmetrical topology makes the negative and positive part of the signal travel in the same type of transistors to symmetrize the non-linearity of these transistors.

The low coloration allows multiplication of this same kind of stage without a too typical sound alteration.

The very high speed of the amplification stage allows the design to be made with negligible frequency tuning. Without phase correction the stage displays perfect (0 degree) phase response in the audio bandwidth. Thus the linearity can be made perfect and the stability of the whole design is maintained with ease and without the strong frequency limitations usually adopted (very detrimental for the sound quality).

The propagation delay of the stage, typically inferior to 80ns, allows negative feedback to be tailored without significant TIM induced distortion. Depending of the position of the stage in the amplification line, this capability allows the designer to use the needed amount of negative feedback, without detrimental sonic effects. Inherent low distortion and stability contribute to free the choice of extremely low or moderate values without significant sonic differences and with a perfect purity of the signal.

To insure a very low DC offset, and keep this offset very constant, the input circuitry of the amplification stage is potted. This technique allows the temperature difference between input transistors to be kept very small. More, due to the very symmetrical topology, the temperature changes have very limited effect on this offset.

It explains why the best MIMESIS products are fully DC coupled without the usual impractical limitations inherent to this kind of design, and without the sonically imperfect DC servo-loop usually encountered in transistor design. This is one important contribution to the famous “liquid” sound and very clean bass response of the MIMESIS line.

The schematics used provides rejection of power supply imperfection of nearly 100dB. The typical induced power supply noise is thus not perceptible. Since the schematics is also very symmetrical, even unstabilized power supply can be used, and the typical high frequency noise of regulators can be avoided.

The total symmetry and the use of inverted transistors in each signal path provide a large insensitivity to the transistor matching. Replacement of a transistor doesn’t affect the balance of the design nor the sound quality.

The plugged input module allows also the maintenance to be made without dangerous fluctuation of the sonic quality.

A single adjustment for each stage compensate for DC offset differences between modules. A very fast DC tuning is so the only adjustment needed after a transistor or input module replacement.