The Pioneer S-RS3W is a powered subwoofer with two ports that I purchased about 2 years ago for
150 dollars (USD). It has a 12 inch woofer cone and is powered by a 180W RMS amplifier.
You can see the plastic cover cabinet that houses the amplifier unit at the rear of the subwoofer.
The back cover is held by 8 philips screws that come right off, exposing the amplifier board and the control board (the control board is still attached to the casing in this picture) .
At first glance the amplifier is bolted heavily onto a large metal plate that holds the entire parts list.
Beneath this metal plate is the subwoofer cabinet wood enclosure.
At the middle of the rear wooden cabinet is a hole whereby the speaker cable goes through and the status LED indicator of the subwoofer go through. More details on this later
Oh hope you noticed the fan screwed directly on the wooden enclosure. This cools the heatsink directly.
I unscrewed the PCB from the plastic enclosure to finally expose the input board and potentiometers.
This board is the JACK ASSY.
There are two RCA entries on the left. One is the signal INPUT and one the signal OUTPUT.
The input goes to an op amp buffer with unity gain that echoes the input to the second RCA port.
Signal goes from that op amp buffer into a phase select switch connected in series with the non inverting input of a secondary op amp that can reverse the phase of the input signal by 180 degrees
From there the signal goes to a Low Pass Filter section (basically a single opamp + potentiometer) connected to it allowing the user to adjust crossover frequency range from 50Hz to 200Hz. The potentiometer knob is visible on the rear of the device for manual adjustment of the cross over frequency.
The Low pass Filter (LPF) can be bypassed thereby allowing non filtered audio from the audio input to the amplifier using an external switch available on the rear of the device.
The JACK ASSY also features the main power switch that turns the unit on and off.
The signal leaves the JACK ASSY to arrive at the POWER AMP ASSY
THE POWER AMP ASSY
There are only 3 boards on this unit one is the JACK ASSY, REGULATOR ASSY, POWER AMP ASSY. In the picture above, the JACK ASSY is on the extreme right, the topmost board is the REGULATOR ASSY, the lowermost largest board is the POWER AMP BOARD.
REGULATOR ASSY
Two power regulators are present on the topmost PCB one is a +12V regulator and the other a -12V regulator.
The +12V and -12V rails along with a GND rail power all the op amps found on the PCB board. The voltage is combined to output 24V to the fan that cools the heat sink of the amplifier board.
The fan has a positive and negative lead as well as a fan control lead (for RPM adjustment)
POWER AMP ASSY
There are two 5600 uF capacitors on the left side of the board (nichicon brand) the output of which is rectified by a non heatsinked bridge rectifier. The operating voltage output of the rectifier is +/- 62 V according to the schematics
POWER AMPLIFIER IC - STK404 140N-E
The amplifier hybrid IC powering this unit is called GODZILLA by Pioneer (insane..) It can produce 180W RMS into 6 ohm load.
THERMAL REGULATION
One thing that puzzled me was the mere absence of thermistors and the like mounted on the heatsink! Turns out the Amplifier Chip has got an internal thermal sensor that is actively measured by transistor logic circuits that in turn adjust fan speed! The following picture is that from the IC datasheet
This picture below is the same datasheet technique applied by pioneer engineers
The woofer is 6 ohms impedance with no wattage description
Whoa incredible you made it to the bottom of this post! Thank you so much readers and hopefully this has been an interesting one
Cheers
Kemley
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