Miscellaneous Projects

Some information on the parts: Supply: 1000 VA/2x42 Vac Amplimo toroid (yields a slightly low 2x 57 Vdc after rectification) 4x 66.000uF/63V BCC elco's bridged by 2x 10 uF Chateauraux SCR polypropylene Preamp/driver circuit: All signal path capacitors: Chateauroux SCR polypropylene 220 uF elco's in signal path replaced by 100 uF polypropylene added second 100 uF capacitor in positive input to improve balance of differential amplifier added some decoupling capacitors across zener diodes FETs: bought 100 x IRF244's which yielded 4 pairs of 12 with a Vgs within 10 mV (maybe an illustration for who needs on estimate on how many FETs to buy: Vgs @ Ids=330mA ranged from 3.89 V to 4.23 V. For every set of 12 fets I have one or two spares within the same <10 mV range differential amplifier FETs (IRF9610) were matched to two pairs of 1 mV out of a set of 20 pieces) Resistors: metal film output resistors (0.47 Ohms): metal-tape induction-free types Heat sinks: Fischer SK56/200/SA, 200x200mm, four pieces per amplifier four heat-sinks are joined at the edges using 2 mm thick aluminium profiles, these provide thermal coupling between heat sinks this gives a hot-spot temperature of  61 degrees Celcius at 460 W dissipation and 20 degrees C surroundings Measured performance: amplification, unloaded, unbalanced input @ 0 dBm input/1 kHz: 23 dB (and 22.9 dB for the other amp) frequency range (unloaded) @ 1kHz: 5 Hz-63 kHz frequency range @ 8.1 W load/1W output: <5 Hz-63 kHz full load output power, no visible distortion of sine wave on scope @ 1kHz: 167 W in 8.1 Ohms 252 W in 4.05 Ohms 164 W in 2.7 Ohms My other equipment Thorens TD 160 Mk1 turntable, lead-shot filled plinth Mission 774 tonearm Ortofon MC30 mkII cartridge Musical Fidelity XL-P phono-amp Mark Levinson No 28 pre-amplifier Wadia 12 DAC CD drive: home-grown Celestion SL700SE speakers. Gerben Poorter