Luxman C12 control amplifier & M12 power amplifier

General:

This pre-amplifier or control amplifier as Luxman likes to call it and power amplifier set was produced in the early 1980’s. 
They are part of the "Laboratory Standard Series" just as i.e. the T12 and the L10.

 

Special futures:

The pre-amp section of this set, the C12 was remarkable because of several features. It employed no tone-control, it did however have a "Linear Equalizer". Below is explained what it does:

All the program sources available are not always perfect.
Record discs, cd's and tapes, as a program source, are liable to have a
slight deviation of linear nature depending on the manufacturers.
For example, all recordings are equalized in accordance with RIAA standard,
but its quite common to encounter variations in overall tonal balance from
one recording to the other.
Also, differences in listening environment and room acoustics often require
a subtle degree of tonal compensation that conventional tone controls cannot
correct because of their wide range and overlapping characteristics.
The "Linear Equalizer" control provides a form of tonal compensation
especially intended for this sort of tendency.
With the control in its mids position, flat frequency response is achieved.
Switched to the "up--tilt" positions, the entire response curve is rotated
on a 1 kHz axis so as a linear increase treble response while simultaneously
decreasing bas response.
Conversely, selection of one of the "down-tilt" positions rotates the
response curve in a clockwise direction, providing a gradual decrease of
treble response and simultaneous increase of bass response.
Degree of slope for either positive or negative settings has been carefully
preset, and the overall response maintains complete linearity
from 50 Hz to above10 kHz, unlike the curvature in response normally
associated with ordinary tone controls.
Specifically, when the control is turned to the max "up-tilt" position, it
will decrease bass and increase treble by 2 dB at 100 Hz and 10 kHz
respectively.
Selection of the max "down-tilt" position will decrease treble and increase
bass by 2 dB at the same reference frequencies.
At the center of the rotation, components which consists the Linear
Equalizer are all by-passed to realize flat frequency response.
The control is inserted in the flat amp circuit and is effective on ALL
program sources.
It introduces no increase of harmonis distortion in any of his settings
because of the inherently linear nature of this circuit.

 

Schematic:

C12 schematic diagram:

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Modifications:

SERVICE WARNING:
When you service the Luxman M12 amp you should be aware of the fact that the power
supply capacitors keep the full +/- 55V = 110 V supply voltage on them when the amp is switched off,
even when completely taken off the mains supply and even after being weeks out of use.
These caps should be discharged by qualified service personel the proper and safe way with 100 Ohms resistors.
If you fail to respect the full & correct manual discharge of the power supply caps,
you will almost certainly damage the power amplifiers and possibly all output transistors,
also improper discharge of these caps may be dangerous for your health.
The output transistors of the M12 are out of production and not sold anymore and
there is NO replacement transistor that is suitable and gives the same exceptional
performance of the Luxman M12 amplifier.
All M12 amplifier models with different output transistors may sound well,
however do not meet the original M12 specs of Luxman.

 

The DML ic's employed in both units are often the cause of problems and need to be replaced by discrete parts.
Of the replacement DML-01 there are 2 different versions. Using version 2 for repalcement of the original DMLs is preferrable.
Of the replacement DML-02 is only one version known. The used discrete parts in the replacements may vary.

 

The schematic diagram of the DML-01 version 2:

 

 

The pcb layout of the DML-01 version 2 is below:

 

 

The schematic diagram of the DML-01 version 1 is below:

 

Below the schematic diagram of the DML-02:

 

User manual:

click here to download the user manual in zip format.

 

 

 

Sound:

These series of "High Quality" audio components soon got ledgendary of their outstanding quality and excelend sound quality.

 

Copyrights: Hans Hilberink - PE1MMK  - 1995 - Last update: 10-08-2010.