General:

Generously build amplifier with good performance, made by Luxman in 1967/1968.

The SQ1220 amplifier is an early fully transistorized stereo integrated amplifier for home and professional use.
It has many features Luxman made the difference with, this model has also generous output power capability.

 

 

 

Special futures:

L&R separate tone knobs with switchable crossover frequencys, like many Luxmans have, a typical Luxman feature.
Power- and pre-amp can be used separately.
Early 2x 50 Watts RMS fully transistorized stereo integrated HiFi amplifier.
Accompanied by the Luxman WL313 FM/AM Tuner.
This SQ1220 is almost identical to the SQ301.

 

 

User Manual:

 

 

Schematic:

Click here to download the service manual of the Luxman SQ1220 in PDF format

 

Top view inside unrestored, lost of dust and rust ^

 

Bottom view inside with worn out electrolytic capacitors made by Nichicon ^

 

Early silicon Toshiba power transistors of excellent quality ^

 

Power amps pcb's ^

 

Modifications:

Be aware of the fact that this amplifier was initially designed for the use of 16 Ohms loudspeakers,
it works however well with 8 Ohms speakers, but an impedance of 4 Ohms will break the power transistors.

This amp had all electrolytic capacitors far out of specs, so all need to be replaced.
Since this amp is quite peculiarly constructed and some parts of the amp are hardly accessable, like the phono stages,
and the amp is not built very service friendly, the replacement of all caps is a lot of work and is very time consuming.
There are some parts, like the pots for idling current, that may be not usable anymore and need to be exchanged.

If you have a multi-voltage unit, set the mains power to 240 Volt AC tap mains Voltage if you reside in Europe,
due to the detrimental voltage rise in Europe, this 240V setting for this amp is very important.

The original schematic diagram does not comply with the actual circuit in this amplifier,
also there are some parts that are obsolete and must be removed or changed in better values.
The power supply needs to be seriously changed and updated.
Replace the 2 power diodes, the original diodes are 1.5A RMS current (!) that is a quite poor value,
I installed 10A - 200V general purpose diodes: no breakdown risk.
The power amplifiers have some serious flaws in the design, that have to be corrected to modern standards.
In fact some parts of the schematic-diagram have to be redrawn to get it right, see the picture below.
The damping factor switch is obsolete, as we want maximum damping factor and all
the other settings of this switch are useless and have a negative impact to the sound.
The local feedback of the power amplifiers has to be changed.
The zobel and compensation circuits of the power amp have to be changed.
The 3D circuit and the connection of pre & main amp has to be updated or removed.
Change the low-cut switch setting into a usable "subsonic" switch.
The crowbar circuit has a negative impact on the sound and
can better be exchanged by a modern protection circuit.
The wiring of the amplifier can be sanitized: some wiring is not needed and some wiring can be improved.
Replace the pilot lamp by a led: install a led circuit with rectifier, resistor and small capacitor.
A new cabinet was made for this magnificent piece of historical electronic amplification technology by Luxman.

 

The output stage redrawn ^
All obsolete parts left out, feedback adjusted, the power supply must be upgraded to use this design.

 

All caps way out of specs ^

 

Some 50% value left ^

 

The 3 old "out of specs" power supply capacitors removed ^

 

All three together just over 800 µF capacity left. ^

 

New capacitors, new diodes, new wiring, set to 240V mains Voltage  ^

 

Replacement of the 3 caps by one high quality 10000 µF 100V LL cap. ^

 

New caps and some new wiring, all useless wiring left out ^

 

 

Old versus new ^

 

^ The 4 output capacitors replaced by 2 modern caps, make ELNA, all obsolete wiring left out.

 

Restore of the phono RIAA section ^

 

Restored and upgraded power amplifier pcb's ^

 

Pilot lamp replaced by a LED ^

 

The Luxman SQ1220 (early version) now with the newly made cabinet, isn't she a beauty? ^

 

Sound:

The sound is very typical for an amplifier of this kind, powerfull and warm.
Due to the +80 Volt single power supply the amplifier has lots of power, but it lacks
a little the finesse of a more modern amplifier of Luxman, like the SQ505x/SQ507x,
but sounds much better than many ie. Sony's etc. of the same age.
Makes a perfect combo with the Transistorized Luxman WL313 AM/FM tuner.

 

 

LUXMAN

Ultimate HiFi