Miscellaneous Projects

Here I present my new project AX to your gallery. I have made Balance Zen, AP and A60. This is my 4th project from Mr. Pass's design. Rail voltage: +/-21.2V giving about 91W at 8 ohms and 60W at 4 ohms load. Filtering capacitor is 47k, then 0.47mh air choke and then 18k + 6800uF capacitor giving about 0.5Vp-p ripple at 6A bias. Transformer is 2 pcs 500VA 18Vx2 for each channel. It is sourced in China with very good price, USD$22 per pc 500VA transformer. Little hum is heard but cannot be notice after closing the top cover. Mosfet are all IR brand and use 16 x IRFP240 for each channel. Bias is set at 3A each side, thus total 6A for each channel. Power up surge limit use 6 ohms 50W resistor and relay at transformer primary. Heatsink is 340mm (H) x 300mm (W) x 84mm (D) and 10kg each pc, thus one channel is about 40kg. Heatsink temperature at about 45 deg C after two hours play (room temp 22 deg C), i.e. about 23 deg C higher than room temperature. Power mosfet source resistor use two 1 ohm 3W (=0.5 ohm) resistors in parallel, R5/R6/R40/R41. Output sensing resistors use 0.68 ohm x 11 pcs in parallel - R2/R42. · R12/R34 all use 1k ohm. Use 4.7k resistor for dc feecback between speaker out and common source. NPN transistor all use BC550C. Feedback capacitor use 10pF in parallel with 100k ohm to give best square waveform. Speaker output to ground use 4 pcs 120ohm 3W resistors in parallel. · Use normal electrical wire single core 2.5mm sq or 1.5mm sq for connecting the power supply and power mosfets. DC offset is about 60mV and thus parallel a 24k resistor to one of the 390 ohm drain resistor to reduce it to about 40mV. No input capacitor is used and after plug in pre-amplifier (DIY Amplifier-P), the dc offset is up to 70mV, both channels within 5 mV tolerance. Total material cost is about $700 USD plus my 6 months spare time to plan, source and build this wonderful amplifier. Sound is firm, clean and base deeper than my Amplifier 60, resolution is very good and can hear the harmonics obviously from recordings. Very musical sound and not tiring for prolong hearing. Here I thank you Mr. Pass, G. Rollins and all DIYaudio.com friends for the details instructions of building AX. Any question is welcome regarding build and sourcing parts. Regards, Spencer Cheung (Hong Kong) .(JavaScript must be enabled to view this email address)

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