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This is an another project based on LM3875 GainClone. As I needed amplifier with XLR input I decided to use four PCB's with LM3875 on board.

LM3875 BridgeClone 1

The whole schematic can be seen here. The case contains four LM3875 boards, capacitor bank, MUR860 bridges, controller board and toroidal transformer for audio design.

LM3875 BridgeClone 2


The gain of single LM3875 was reduced to 10x to give total 40x after bridging and with simetrical input from my preamplifier. Power supply capacitors are 1000uF/50V Panasonic FC. In gain path there is 100uF/50V Panasonic FC and WIMA 2u2 at the input. All resistors are 1% metal film.


The capacitor bank is a simple CRCRC ladder with total 25000uF per side. Used capacitors are Rubycon and there are two Samwhaw's that I had from other disigns. I decided to use additional capacitors, not just 1000uF on LM3875, because the whole project was ment as a POWER amplifier, not just to be listen gently in the evening.

power supply


The main reason for this board was to have outpur rely delay. The circut contain also debouced power on push button with two-colour led. Te whole amplifier can be also remotely power on or off using CNY17 optocoupler on the back panel. Here you can find the schema.

LM3875 BridgeClone 3


A standard steel case with aluminium front panel. It was made as simple as possible just to fit with my preamplifier. Only one button on the front panel and input, output and power connectors on the back panel.

LM3875 BridgeClone 4

RMAA tests:


Overview | Design | Controller | Case


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