The SKpre has been designed primarily as a simple to use x 4 or 12dB gain line stage preamplifier complete with it's own close mounted 80dB discrete regulators and power supply. The single channel module has a 10K log taper input volume control feeding the fully conplementary differential high gain bootstrapped input stage using matched pair high gain low noise transistors. This is followed by the low gain 300MHz transistor Class A output stage allowing Class A operation to 10mA output. Simple but effective 2 transistor bootstrapped regulators ensure a supply impedance of less than 10 milliohms, and greater than 80dB regulation across the audio bandwidth for excellent low noise supply performance.

In addition, the module includes an indicator LED and being totally DC coupled, DC offset adjustment. The active stage can be wired in inverting mode to provide an inverted signal for balanced outputs and for I/V interface on DAC outputs. It can also, with a couple of minor component changes, be configured as a balanced in to unbalanced out unity gain buffer for power amplifier inputs. The PCB is fully ground planed, with through hole plating, and component placement overlay for an easy build, with very low noise and interference. RF filters take care of stray RF pickup without impacting the audio bandwidth.

The unique topology of the SKpre in conjunction with the local 80+dB discrete low noise regulators ensures very low noise and distortion maximising transmission of spatial and timbral detail

 

skpre.jpg
 Freq. Response DC
3mHz -3dB
 Audio Band
20 - 20KHz -0.1dB
 Distortion
< 0.001% 2HD only
 Input Impedance
10Kohm
 Output Impedance
47 ohm (user defined)
 Noise
< -120dBA below 2Vrms out
 Rated Output
2Vrms
 Maximum Output
10Vrms
 Output Current
10mA in Class A
 Supply Current
7.5mA
 Supply Voltage
30Vac CT or 15Vac or +/-20V
 Dimensions
75mm x 50mm x 30mm

DualSKpreReg, a low power dual reg as a standalone item for use on applications up to 50mA but typically in the 10-30mA range and fixed (different resistors for different voltage builds), ideally suited to independantly powering circuits such as the OptiVol, that requires 30V at 14mA. It is a combined 2A discrete bridge, two 2200uF 25V supply storage caps and the two 2 x 300MHz BJT low noise bootstrapped discrete regs. It uses an active Vbe + noise bypassed green LED for reference. The output has 1uF monolithic (ceramic) bypass caps and 2mm hole screw terminal block.

It is all ground planed and may alternatively derive it's power from DC supplies such as power amp supplies, using dropping resistors. AC power can be from a 15Vac plugpack or 30V CT transformer, for +/-15V DC output.

skpre.jpg
 Input
15Vac or 30Vac CT or +/-20V to +/-24V DC.
 Output
+/-15V DC +/-5% at up to 30mA
Regulation
 typ 86 dB to 20KHz.
 Output Z
typ 15mOhm
 Output Impedance
47 ohm (user defined)
 Noise
 < 3uV 20-20KHz Awtd.
 Dimensions 43mm x 51mm