MM cartridge is capacitively loaded by C100, C200. These capacitors are rather optional since the modern MM cartridges require only low capacitive loading (~100pF) that can be technically implemented by signal cable connected between the turntable and the input of the pre-amp. Input stage uses externally compensated (C105, C205) low-noise bipolar OPAMP NE5534AP. Full RIAA correction is implemented in the feedback loop of input stage to allow maximum signal headroom. Necessary time constants are precisely defined by serial/parallel combinations of resistors and capacitors. Capacitors C101, C201, C102, and C202 reduce DC offset without compromising distortion and low frequency amplitude and phase response. 

Input stage is followed by 3-rd order subsonic filter eliminating dangerous subsonic signals that can easily damage low-frequency speakers when warped vinyl record is played at high volume levels. Circuit uses dual low-noise OPAMP and high quality capacitors with polypropylene dielectric material. Output circuit provides also additional time constant (R108, R208, C111, and C112) to perfectly linearize RIAA response in high frequency range.

Next stage is voltage gain setting circuit allowing precise overall gain setting in range from +36dB to +48dB with 3dB step at 1kHz. Voltage gain stage allows the user to perfectly match voltage level of used MM cartridge to the input of electronic device (sound card, amplifier, etc.) connected to the output of pre-amplifier.

Output circuit (IO3) is configured as ground-cancelling output with phase-lead compensating capacitance (C115, C215). This circuit allows to insert parallel RC impedance info the shielding path. At the first sight this may seem to be crazy idea but in practice it works very well. If there is problem with grounding loop in the setup, addition of RC impedance into the shielding loop cans significantly improve system performance. This feature is optional and can be disabled by jumper JP3-1.

Power supply is using 5V to ±15V DC-DC converter to provide adequate, symmetrical power supply voltages for OPAMPS. Input circuit contains common mode noise filter, overcurrent and overvoltage protection and differential filtering circuit (C8, C9, L2, C10-C12). Outputs are first filtered by RC network with ultra-low ESR polymer capacitors. This circuit is then followed by symmetrical BJT capacitance multipliers. Diodes D2, D3, D6, D7 provide protection of transistors. 18V Zener diodes connected in parallel to C20 and C21 provide overvoltage protection of OPAMPs. LED diode indicate presence of power supply voltage.

Fast starting, symmetrical power supply helps to eliminate unwanted transients during power-on and power-off.

Pre-amplifier provides ultra-low noise, ultra-high accuracy of RIAA correction and excellent overall sonic performance.


Technical parameters:

RIAA accuracy ... < ±0.1dB in range 20Hz to 20kHz
THD ... < 0.008% in range 20Hz to 20kHz (output level -10dBV)
Signal headroom ... > 28dB (output level -10dBV)
Signal to noise ratio ... > 82dB, > 87dB (A-weighted)
Voltage gain at 1kHz ... +36dB to +48dB, selectable with 3dB step
Subsonic filter ... fc=20Hz, Qt=0.7071, 18dB/oct. (Butterworth)
Power supply requirements ... +5V / max. 250mA, USB type-B
Total power consumption ... < 1.25W