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)

 

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 ^

 

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

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 ^

 

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