Monday, October 15, 2012

SynergyII\Cu LM3875 compact chip amp

SynergyII\Cu started with 3.6kg of 100% very thick copper plate. The enclosure was selected, a 1U, 19” rack mount. The challenge was to build a pure Gainclone with its three resistors and simple 1500uf storage caps in a compact 1U enclosure. Everything had to fit in this tiny space including 48VAC of tranni, power filters and rectifier cct.

To achieve this two 24V ultra low profile toroid trannies were selected, the rec. cct. brd. was constructed on a tag strip with super fast, soft recovery diodes (snubbed with 0.01uf polies) and a compact EMI\RFI power filter installed across the mains. A pseudo smoothing cct. is provided with a couple of 4.7uf polies on the differential voltage rails. The 1500uf electrolytic are snubbed with 0.1uf polies at the chips.  A simple ferrite choke sat around the power cord inches from where it entered the amp.

Solid 0.4mm five-nines pure silver wire connects the earth point on the PS to the input RCAs and speaker binding post returns. Heavy multi stand copper wire connects the differential PS, individually, to each chip amp cct. Total weight is 9.6kg. Being a DC amplifier bass is extended and controlled. The sound is clean, clear and solid with plenty of power.

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