This project is similar to the other BOSE accoustimass projects but allows standalone operation without using the BOSE DSP module as it is bypassed. This allows operation without having to send any serial commands to the bass module as the six audio amplifiers are connected directly to a low level audio source. This could be a PC's sound card analogue outputs or a stereo preamplifier. 

DOLBY and DTS decoding-

If you use a sound card that supports Dolby Digital or DTS decoding with output to the cards analogue outputs you will get the correct surround sound effects on the AM-25/30 used in this way, not bad for surround sound system more than 20 years old!

There are also other options for using the AM-25/30 in this mode. There are TOSLINK input to six analogue channel output boxes that will carry out Dolby digital and DTS decoding, I have seen these on eBay for about £20.

When using the AM-25/30 Module in this direct drive mode you may have to setup the PC or amplifier audio outputs that drive the bass speaker for the correct low pass cut off frequency. The other five channels may also need high pass characteristics setup depending on the crossovers and characteristics of the smaller speakers. When using a PC sound card there is usually a setup program which allows you to adjust these settings. Many HiFi pre-amplifiers have a sub woofer output and this may be adjustable (or fixed), you need to consider this when driving the AM-25/30 BASS power amplifier directly.

So in some circumstances the bass amplifier may need to have an analogue low pass filter fitted to it's input. The bass servo amplifier MUST NOT be driven for long periods at frequencies above about 500 Hertz (cycles). 

There are two options to use the Accoustimass 25/30 bass module directly connected in this way:

ONE- Short the mains supply power control Triac signal so that the unit powers up when plugged in and apply the low level audio signals directly to the power amplifier PCB within the bass module. This is the simplest way to use the bass module but it also bypasses the BOSE microprocessor error inputs which are located on the DSP PCB. These inputs check the six audio amplifiers for DC offsets at their speaker outputs. So if you are using good quality speakers you may want to use method two below.

TWO- Use a PP3 9volt battery or a small mains 9 volt power supply to supply the "power ON" signal to the accoustimass bass module and wire the low level audio signals directly to the six amplifier inputs. This method allows the bass module's  amplifier DC output protection circuit to work by switching off the mains supply to the accoustimass unit if there is a DC offset error on any of the six amplifiers outputs, which is preferable if you have good quality speakers attached to the stereo/centre/surround amplifier outputs and it also protects the two 5.25 inch bass speakers in the accoustimass cabinet. A PP3 battery will last about 18 - 24 months of daily use.