HIGH FIDELITY SOLID STATE AMPLIFIER part 2
CLICK HERE FOR CIRCUIT, COMPONENT LAYOUTS AND PCB TRACK PATTERNS
CLICK HERE FOR ASSEMBLY DETAILS AND PHOTOGRAPHS
DUMMY PCBs USED TO CHECK FIXING LOCATIONS
THE ETCHED PCB, READY FOR DRILLING
(right) the built amplifier before additional heat sink fitting
INTERNAL LAYOUT PLAN
Component list for LM3886 amplifier
LM3886: Mouser £4.38 + VAT, 2 off
4 off 10µF 50VW audio grade electrolytic capacitor, Mouser 647-UFG1H100MDM @ 18p ea
2 off 47uF caps. Mouser 647-UFW1H470MED @15p ea.
4 off 10µF 100VW electrolytic caps. Spiratronics FF4-570 @ 0.06 ea.
2 off 47pF. Mouser 581-SR151A470KAR @ 16p ea
2 off 220pF. Mouser 581-SR151A221JAR @14p ea.
2 off 47k RC3-703 Spiratronics @ 0.04p ea.
4 off 1k RC3-369 Spiratronics @ 0.04p ea.
6 off 22k RC3-637 Spiratronics @ 0.04p ea.
2 off 10Ω RE3-132 Spiratronics @ 20p ea.
2 off 2.7Ω Rapid 62-7957 @12p ea.
1 off Dual pot, 22k 16 mm body. Rapid 50-7855 @ £2.71 ea.
Mains trx: Rapid 88-3828 @ £30.13. +-18v, 225VA toroidal
1 off bridge rectifier: Rapid 50-0273 @ £0.52p each. KBPC801 8A 100V.
2 off 10kuF electrolytic capacitors. Mouser 647-UFW1H103MRD, 50VW audio grade @ £2.81 ea.
*On-off switch. Spiratronics TW3-525 rocker type @£1.18
4 off capacitors, 0.1uF 100VW: Rapid 10-5770 @ 0.0515 ea.
*1 off LED
*1 off LED load resistor
Heat sink compound, Wacker. Rapid 50-2417 @ £1.19
Heat sinks: Ebay ordered.
Heat shrink tubing. TW1-685 Spiratronics, 3.2mm black 1.2 metres at £1.44 ea.
Heat shrink tubing. TW1-650 Spiratronics, 6.4mm black 1.2 metres @ £2.09 ea.
PCB mountings: FW3-490 Spiratronics @ 0.09 ea.
2 off phono panel mount socket, red. Rapid 54-4725 @ 92p ea
2 off phono panel mount socket, black. Rapid 54-4726 @ 92p ea.
1 off Control knob: Rapid 32-1856 @ £2.26
Photosensitive PCB 203 X 114 £5.78 ea. Spiratronics. Alternative: Mouser 590-606 £5.81 plus VAT ea.
1 off IEC chassis connector. Spiratronics. PS2-010 @44p ea.
Prices correct at time of construction
Dimensions of chassis:
215mm deep, 200mm wide and 88mm high (not counting top heatsink cover of 180 mm X 75 mm X 15mm, nor the feet which add about 3mm to overall height). The three main panels: Base panel 215mm X 212mm. Front and back panels, each: 200mm X 90mm.
Dimensions of cover:
(shown in above photograph): 215mm deep X 90mm high (All dimensions approximate)
Sprayed with grey car body primer and finished with blue semi-gloss enamel aerosol spray
BRIEF CIRCUIT DESCRIPTION
The LM3886 is a high-performance audio power 23-68W Cont. Avg. Output Power into 4Ω at VCC = ±28V amplifier capable of delivering 68W of continuous average power to a 4Ω load and 38W into 8Ω with 38W Cont. Avg. Output Power into 8Ω at VCC = 0.1% THD+N from 20Hz–20kHz. ±28V
This design uses a ± 28V toroidal transformer which is both economic and efficient. It is built into an aluminium chassis and casing.
Rear panel carries line in RCA sockets, loudspeaker connectors and a standard IEC kettle-type 3-pin mains input socket.
The large heat sink is only necessary when thin loudspeaker connecting cable is used. I recommend the use of household mains wiring cable of the solid core type. Any heat sink should be mica-insulated from the metal tabs of the LM3886 and heat-sink compound should be used.
The component list to the left details all the original parts. Some substitutes to the constructor's choice may be used but it is prudent to use closely similar values of capacitors and resistors.