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Subwoofer Operation



amBX - Subwoofer / Amplifier / Speakers


Introduction

The subwoofer and speakers form part of the premium kit. With one exception (the mains relay), the subwoofer has nothing to do with the amBX system, other than the wallwasher is used to connect the speakers to the amplifier. A failure of the subwoofer will not affect the working of any of the lights, fans or rumbler. The subwoofer does not use any software or drivers. The amBX drivers and software only relate to the working of the lights, fans and rumbler.  


The subwoofer consists of three main parts:

Amplifier and speakers

Power supply (PSU)

Mains relay

None of the items in the subwoofer box are easily accessible.

The PSU is contained in the subwoofer box and is connected to the mains plug via a mains relay.





Fig. BO1:  Block diagram of the subwoofer components and its connections



Amplifier and speakers

The amplifier has three outputs:

Subwoofer speaker (inside the subwoofer box)

Left speaker, right speaker


The input to the amplifier comes from the green 3.5mm audio in jack socket on the back of the subwoofer. A cable connects this socket to the Line Out / Audio out (normally green) socket on the PC. Although it’s usual to connect the sound from the PC to the subwoofer, it is possible to connect a sound source from other devices, such as an i-pod etc.


The output from the amplifier to the speakers goes to the wallwasher through the 7-pin mini-din audio in cable and then to the speaker via the speakerlight cable. This is a direct through connection between the subwoofer and the speaker, and the wallwasher has no effect on the operation of the speakers.


Volume control

There is no direct volume control for the left and right speakers. The amplifier is always working at full volume. Instead of controlling the volume output of the amplifier, the audio input level is controlled instead. Thus a low audio input from the PC will give a low volume and a high audio input will give a high volume.


The speakerlight has a volume control on it, but this is a software control and works by sending a command to the PC. It has a similar effect to when you change the PC’s volume by clicking on the PC volume control. Because of this, if you were to connect a different sound source to the subwoofer, the volume control on the speakerlight has no effect because the subwoofer will not be connected to the PC. Use the volume control on the sound source instead.


Because the amplifier volume is always high, you may notice a quiet hum on the speakers when there is no sound going to the speakers.


The subwoofer has a bass control on the front. This controls the bass level on the subwoofer speaker


Power supply / Mains relay

Unlike the wallwasher, the subwoofer does not have an external PSU. Instead, it connects directly to the mains supply. The PSU is a self-contained sealed unit within the subwoofer box.

I have not taken the PSU out, so I don’t have any details or specifications for it.


There is no mains switch on the subwoofer, instead there is a mains relay inside the subwoofer which connects between the mains input and the mains supply to the PSU. This acts as a mains switch. The relay is energised (closed) by 5v from the wallwasher which passes through the cable that connects between the wallwasher and the subwoofer. Even though the subwoofer is plugged into the mains socket, it will not work unless the wallwasher is switched on and working because the relay will not be energised and closed.


The relay will only be closed when the wallwasher is ON and there is a working USB connection. If the walwasher is put into standby, the relay will open and the mains supply to the subwoofer will be switched off.


The “click” you hear when you turn the wallwasher on or off is the relay closing or opening.

(You will not get the click when switching the subwoofer mains on or off (at the plug, or plugging it in) because the subwoofer mains doesn’t control the relay).























Fig. BO2:  Subwoofer power supply connections



For the wallwasher to be turned on and fully operational, it needs to be connected to the external mains supply and needs the USB cable to be connected to the PC.  

Therefore, for the subwoofer to work, it needs the:


Subwoofer plugged into the mains

Subwoofer cable connected to the AUDIO IN socket on the wallwasher

Wallwasher PSU plugged into the mains

USB cable connected between the wallwasher and the PC

PC switched on

Wallwasher switched on and working


It also needs an audio input plugged into the wallwasher audio in jack socket if you want sound to come out of the speakers.