Luxman L-55A amplifier

 

General:

Around 1982 Luxman company came with its L55A amplifier

 

Owners manual:

click here to download the owner manual of the L55A in pdf format

 

special futures:

 

 

Schematic:

click here to download the service manual of the L55A in pdf format

A complete service manual is not yet available, only the part above.

 

 

Sound:

The sound is very good.

 

Modifications:

Some pcb boards are not very well servicable, you have to dismantle half the amp to get to the parts.

Check DC offset and idling current of the power amp, check dynamic feedback of the power amp.
Check thermal drift of the idling current and DC offset.

Check anti-oscilation capacitors of the power amp section, this amp is a triple-stage amp and may suffer
HF instability.

Remove any pcb that some local distributors inserted in the pre-amp, like the board on the photo below
of Audioscript Netherlands. These boards are subject of several problems, like popping sounds when
operating the subsonic switch, and DC problems. These boards do not meet the quality of the amp.

Check the speaker protection circuit, it is sometimes not operating properly. Check the thermal situation
of the power amp board, the first section of the power amp may have thermal issues, heatsink the
phase circuit and replace resistors in this part and check resistors of the drivers.

Set the amp to 240 Volt in Europe, as many countries have 230 Volt mains in stead of the former 220 V
Keep the main amp voltages under +/- 55 Volt, If voltages of the main amp get too high the amp may be instable.

The pcb board by Audioscript. The quality of the parts on this board do not meet the Luxman standard.

© Hans Hilberink - PE1MMK ® 2003, Last update: 04-03-2012.