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CONSTRUCTION PROJECT

HIGH FIDELITY SOLID STATE AMPLIFIER part  3

CLICK HERE FOR CIRCUIT, COMPONENT LAYOUTS AND PCB TRACK PATTERNS

CLICK HERE FOR COMPONENT LIST AND CHASSIS DIMENSIONS

 

 

DUMMY PCB USED TO CHECK FIXING LOCATIONS

 

COMPLETED PCB KIT

 

A VIEW FROM THE LEFT OF THE CHASSIS

 

A CLOSE-UP OF L1 (2 off required)

 


DESCRIPTION

The LM3886 is an integrated circuit containing a high-performance audio power  amplifier which can operate with a wide supply range of 20V - 94V.

With the ±28V power source used for this version of the amplifier, it is capable of delivering 68W of continuous average power to a 4Ω load and 38W into 8Ω with 0.1% Total Harmonic Distortion and a frequency response from 20Hz–20kHz.

The LM3886 maintains an excellent signal-to-noise ratio.

The amplifier is housed in an 11-Lead TO-220 Package.

 This allows the construction of an easily built, powerful and high quality solid state amplifier. It should be noted that the printed circuit board design offered on this site has proven itself to work well.  The component  layout drawings are given as a guide and can be used together with the PCB patterns and the specified components to construct a successful amplifier. The full schematic circuit including a power supply is provided and should be studied carefully to ensure understanding before building begin. There a full list of components as used in the prototype, priced (where possible) with sources of supply. Prices are those which were in force at the time of building and will obviously be subject to increases as time passes. There is no reason why other makes of components should not be used but it is advisable to purchase parts, especially the large mains transformer, before the chassis and top casing is made to avoid problems with oversized parts.

Inspection of the photographs will show that card-mounted paper print-outs of the PCB designs were made to aid location of the mounting pillars and it is recommended that constructors do the same. 

The amplifier chassis is made from 16 gauge aluminium sheet, in three main panels – back, front and base plate. Aluminium brackets carry to PCB support pins. The top cover is a single panel of aluminium, folded to form the top and sides. It is secured to the chassis by self- tapping screws. All chassis and casing parts were made using 16 gauge aluminium sheet and basic tools. You will find a small bench or clamp-on vice useful, and thick blocks of MDF or plywood will assist in the folding of the top cover. 

A toroidal mains transformer was chosen for a number of reasons, among which are cooler operating temperatures and lower magnetizing current. Toroidal transformers have a higher efficiency when compared to traditional types and tend to have reduced height, useful for a slim case such as this one.

 Two aluminium extending plates bent at 90 degrees were bolted to the board-mounted heat sinks and were used to allow the fixing of the large finned heat sink. This heatsink is not essential as long as thick cable such as house wiring cable is used to connect the loudspeakers. Even so it is probably advisable to increase the heat sink area within reason to prevent possible overheating of the integrated circuits.

 

L1 consists of about 18 turns of heavy gauge enamelled copper wire. If you have access to an LCR bridge, aim to create an inductor of 0.7 Henries. The gauge should be chosen to be self-supporting - 16-18 swg should suit. Note that the enamel was shedding itself from the original windings as seen in the photograph above, but this has no noticeable effect on the amplifier performance. Do not allow the turns to touch copper to copper.

                                        


 

 

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