LuxmanSQ 503 (X)integrated amplifier
General:
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Around 1970 Luxman company came with one of its first 'high quality' integrated amplifiers on the European market.
This amplifier was a modern design with excelent characteristics.
It had a full complementary output stage and a differential input stage of the power amplifier.
It is symmetric supplied and the power supply stage was generously built for a 2x30W amp.
The SQ503 without the X is an earlier version that lacks the modern electronic design of the X version, but looks quite the same.
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Luxman SQ 503X
After 40 years + the outside is looking very good.
Before the update the inside looks like this.
Inside the amplifier, top view, new transistors, drivers and output after the update.
.
Bottom view.
Special futures:
Specifications in txt format click here.
Schematic:
Sound:
The sound of this amp is a pleasure to listen to, as the basic schematic diagram design is very good and quite timelessly designed.
Modifications:
This amp needs to be updated as the transistors and the capacitors are outdated.
Many capacitors can be replaced by recent types.
Set the power amp DC offset and the idling current of the power transistors.
The transistors of the pre stages are often noisy. Use BC550/560C or equivialent,
you can get the noise figure below the original specs of Luxman.
The drivers are often defective and the power transistors of the output stage may be obsolete.
The final power transistors are TO-66 cased NEC 2SA616 and NEC 2SD155, they are not available anymore.
The ledgendary 2SC1445 TO-66 transistors and PNP equivalent 2SA765, of Sanken
are of exceptional quality and are the perfect replacement, but hard to get today,
the only plastic replacement is plastic transistors like 2SB595/2SD525 of Toshiba or equivalent,
you have to change the mounting on the heatsink somewhat when you use plastic transistors,
and you may find in some cases that the sound quality will not be the same anymore.
I used BD139/BD140 and BD 292/BD437 of STMicroelectronics and 2SA1694 & 2SC4467
of Sanken as you can see on the photo: works great.
The pcb of the main amplifier.
© Hans Hilberink - PE1MMK ® 2003 - Thanks to: Rob Schonkeren - Last update: 30-06-2014.
Centco CE-300A amplifier
General:
Around 1970/1972 issued solid-state stereo amplifier for international markets made in Japan.
This particular amp was initially bought in the EU as international version, but was also sold in USA & Asia.
front unrestored ^
Owners manual:
Click here to download the user manual of the Centco CE-300A amplifier. (construction)
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Front detail ^
Special futures:
This amplifier comes with cinch input sockets.
Light and small footprint amp.
Metal case.
Exceptionally well build and good parts used.
This amp employs all silicon transistors.
The pcb's of the amp are sitting horizontally in the amp.
This amp is very service friendly, a real pleasure to work on for the technician.
Testing the unrestored amp ^
Amplifier interior unrestored ^
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Specifications:
Centco CE-300A
Power output: 15 watts RMS per channel into 8 Ohms (stereo)
Frequency response: 10Hz to 30kHz +/- 3dB
Total harmonic distortion: 0.1% at RMS output
Damping factor: >40
Input sensitivity: 3mV (phono magnetic), 80mV (phono ceramic), 300mV (line)
Tape-out rec. sockets
Signal to noise ratio: better than 70dB (mag), 75dB (line)
Speaker load impedance: 8 to 16 Ohms (minimum)
Semiconductors: 18 x transistors, 8 x diodes
Solid aluminum front plate.
Weight: 8lbs
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Year: 1970-1972
Pilot lamp ^
Schematic:
Click here to download the schematic diagram of the Centco CE-300A amplifier in PDF. (construction)
Power rail main voltage is -40 Volt assymetric, the power transformer has only a 230V~ connection:
consequently due to the detrimental power change to 230V in Europe the voltage of the power rail is too high.
Power supply - is connected to ground.
OTL and DTL class AB push-pull power amp section.
Direct DC coupled power amp section.
Complementary driver stage, semi-complementary power stage. The pre-amp is partially AC coupled.
All Sanyo and NEC silicon transistors inside.
This amp is produced by Centco Japan, a subcontractor of Rotel, Sansui and some other companies,
this subcontracting is quite common in Japan.
This Centco amplifier uses the same make pcb's as Rotel and a few other companies at the time,
although the pcb's in the Centco amp are better designed.
The better pcb design makes it very easy for Centco to build an overall better designed amplifier,
where Rotel skimps somewhat on design time, electronic parts and other things,
Centco hardly does that and the Centco CE-300A shows inside that it is a better amp than its competitors.
Rotel had a slightly different approach to audio-electronics.
Resemblance with the Rotel vintage amps ^
Power amp pcb with power transistors directly soldered into the pcb ^
RIAA phono amp pcb ^
Modifications:
I replaced some diodes, capacitors and resistors in the power supply and power rail.
Also I exchanged the speaker output screws for sockets as they were of bad quality.
The power rail capacitor was out of specs and had to be replaced.
The power transistors 2SD313C by Sanyo are of exceptional quality, the drivers are 2SC853 & 2SA545.
Check DC offset after restoration, set to approx.19,5 V.
The pre-amp sections all have 2SC945 and 2SC900 NEC transistors used.
Sometimes one or more of these transistors can produce some hiss, in this case exchange is advised.
This Centco CE-300A amp has - to ground.
The power-supply diodes were 1A 100V types 1N4003, these were replaced by 10A 500V general purpose diodes.
The already 'star' grounding topology should be extended by 2 wires at least, to complete the grounding as it should be.
Also the power line - leads (red) should be extended by 1 wire to get the power rail right.
The main power supply capacitor was way out of specs and had to be exchanged, also all power-rail caps,
some cap values may be increased. The driver transistors can be heatsinked.
After the restoration the output power is higher:
2x 18 Watts RMS at very low distortion levels. This amp sounds perfect.
Bottom view unrestored ^
Restore almost complete inside: power-amp ^
Restore almost complete inside: phono-amp ^
Ready: new caps & wiring: (same wire-colouring respected), sound is perfect. bottom view ^
The restored back panel. ^
Rotel power amp section, almost identical ^
Realistic power amp section, almost identical ^
Comet power amp section, almost identical ^
Luxman power amp section, almost identical ^
Ferrograph power amp section, almost identical ^
Rotel phono amp section, almost identical ^
Sound:
The sound is exceptional, powerful and distortionless for such a small 2x 15 Watts amplifier.
Great product made in Japan, this amp will play fine again for many years to come ^
Presented to you by ON9MMK on:
The vintage website.
© Hans Hilberink - PE1MMK - ON9MMK ® 2002 - Last update: 31-08-2019.