Subwoofer Amplifier

          The amplifier used in all Osborn Subwoofer is custom designed for Osborn loudspeakers by Redgum (The amp with the key). Redgum manufacture some of the best amplifiers available at any cost and is proudly designed and manufactured in Australia. Only premium quality components are used. Extremely high quality Audiophile grade mosfets are used instead of the cheap Output IC's used in many other Subwoofer Amplifiers. A quality Power Supply is used, utalising a High Speed Torroidal Transformer. Many lesser subwoofer amplifiers rectify the mains voltage directly, resulting in a cheaper, but inferior performance. Auto switching was tried but rejected as these circuits are always troublesome, switching on and off at inopportune times. The amplifier is designed to be left on at all time so it is always at optimum temperature. Power consumption at idle is minimal.

           It is this no-compromise approach which results in the sound quality attained by all these units. The amplifier was originally designed to be made in either a 180, 300 or 500 watt version. However the performance is so outstanding with the 180 watt unit, that the 300 and 500 watt version is unnecessary. The problem with having so much unnecessary power is the extreme heat generated. 500 Watts equates to 180 degrees Celsius, which is a major problem in a wooden cabinet. This is why competing designs use switch mode power supplies to avoid this heat generation, thus compromising performance for impressive power claims. The Monumental and Ultimate use a larger power supply and more output devices and output 200 watts at 8 ohms and have a better dynamic ability. The Twinultimate uses a 300 watt version of this amplifier. Remember competing manufacturers usually rate their amplifiers into a 4 ohm load. This is an easy and economical way of being able to claim impressive power outputs.

Most subwoofers are designed to output large amounts of woofy bass in the 40 to 80 Hz region. They may be loud, but drone excessively and lack impact and the ability to reproduce frequencies which can be felt rather than heard. Large drivers are stuffed into enclosures which are hopelessly too small, simply because they look impressive to a prospective, but uninformed customer. Because there is no low frequency generated at all, the designer is forced to feed in excessive equalization to try and force the driver to generate frequencies well below its abilities. Any audiophile is well aware what an amplifier sounds like with the loudness on and the bass turned right up. There is bass, but not a realistic and powerful reproduction of the original performance. More like a rumbling mess.

Osborn subwoofers employ no equalization. Bass extension is achieved by careful design and outstanding bass drivers.

Osborn subwoofers are not designed to blow out windows and loosen dental fillings, but for realism, depth, sonic integrity and sheer satisfaction, they are unsurpassed.


          All subwoofers can be connected to a low level input or a high level input. The low level input are for direct connection to a pre amplifier or Home Theater Amplifier Subwoofer output. If the left and right inputs are connected the amplifier will mix and reproduce the signals from both channels.
          The high level inputs are provided for use where there are no low level outputs, such as in integrated amplifier. A second pair of speaker cables will need to be connected to the output terminals of the amplifier and connected to the relevant binding posts of the amplifier. This enables the subwoofer to sense the bass information of the music and reproduce it at whatever level is desired. Naturally the performance will be generally better using the low level inputs if possible, as sensing a high level input does introduce some unavoidable distortions.

Power output:

Subwoofer: Power Output:
T12, T15 175W Rms continuous - 351W Rms short term transient (100ms)  
Ultimate,Monumental, FC12, FC15 Hi Power transformer - 195Wrms continuous - 351Wrms short term. (Larger power supply) 


Frequency response  (relative to 20hz/0db) - minus 3db points are 1hz and adjustable from 20hz to 200hz 
Damping factor   >200 (calculates to 205.128!) 
Input sensitivity  220mV for 175Wrms 
Signal to noise  (output stage) >110db  
Signal to noise  (overall) >85db  
Slew rate  (overall) 35v/uS  


Power supply & all internal wiring Linear Xtal 130amp  
Torroidal power transformer  
IEC standard power input socket 
High power, Audio Grade, thermally stable MOSFET output stage  
Mosfet I/C in filter stages. 
All high current paths are designed for minimum length  
Every power supply lines is bypassed with plastic caps.  
All connections are silver soldered for better sound, longer life and reliability.  
All Australian made - all Australian Design 


Osborn Loudspeakers are designed for the ultimate reproduction of the original performance. Therefore we have approached the design of our subwoofers a little differently to other Manufacturers.

          Many subwoofers provide low level outputs. We consider this unnecessary, especially due to the quality and expense of the connectors used in this amplifier. We cannot see the logic of extremely long and expensive interconnect cables running from a pre amplifier to the subwoofer and then back to the main power amplifier. This would also result in the main amplifier signal needlessly passing through part of the subwoofer amplifiers circuitry. If necessary a splitter can be used closer to the pre amplifier.
           Many subwoofers also provide high level outputs where the signal is passed through an active crossover network, removing the very low frequencies delivered to the main speakers. This also goes against the philosophies held by Osborn. Firstly passing the main speaker signal through this crossover will cause unavoidable degradation to the signal. It is impossible to pass a signal through any electronic components without affecting it in some way. Secondly the removal of low frequency information delivered to the main speakers may allow them to be played louder, but if the speakers are quality units, such as an Osborn model, then they are better suited to reproducing the removed frequencies than any subwoofer.