Component Reviews

TBI Magellan MGD-200 Subwoofer Amplifier SRP: $700

The thought of putting electronics in the most highly resonant area of your system seems counterproductive.

Published on May 9, 2010

TBI Magellan MGD-200 Subwoofer Amplifier  
SRP: $700
TBI Magellan MGD-200 Subwoofer Amplifier  
SRP: $700

TBI Magellan MGD-200 Subwoofer Amplifier 

SRP: $700

TBI Sound
878 Kurtz Rd. 
Suite 101
Marietta, GA 30066

The TBI amp was built to go along with their Magellan subwoofers. I reviewed these subwoofers in this publication in the past: VI SU SubwooferVIII SU Subwoofer + power amp.  [In the meantime the company name has been changed from Thoroughbass to TBI…Ed.]  The TBI subwoofers are my choice of subwoofers to use in any music system. I currently have seven of them in three different systems and it works well in all of them. They are fast enough to fit seamlessly into a ribbon speaker system.

The subwoofer is the component that usually requires the greatest control of any component in a system. Bass needs lots of air motion and control of that air motion. A 32-cycle note is about 35 feet long. This means that the woofer needs to create a 9 ft. rising-intensity quarter wave, then 9 ft. of lowering-intensity quarter wave, then 9 feet of rising-negative pressure quarter wave, then nine ft. of declining-negative pressure quarter wave. And this is done 32 times per second. This takes a great deal of control to do it right. Many subwoofers use large woofers, with long throws to move large amounts of air. The more mass and traveling distance of these drivers causes more inertia, and this causes problems with controlling the movement of the driver. Some high end subs have built in multi-thousand-watt amps to control the cone. Other sub manufactures use several smaller drivers to move the air. Smaller drivers are faster and easier to control, but create other problems for an amplifier. Most subwoofers run at fairly high distortion rates.  The unique design of the TBI Magellan subwoofers greatly reduces the need for inertia control and therefore amplifier control. It also makes the TBIs more tonal and controlled sounding.

One thing most subwoofer manufactures do is build the amplifier into the subwoofer box. They do this because the subwoofer buyer will not have to fork out the money for an extra amp and crossover. I feel that putting the amp in the subwoofer is a very bad idea. A conscientious audiophile spends lots of money trying to eliminate vibration from his electronics. He may use isolation feet and platforms, non-resonant shelving, damping devices and mass loading to try to have vibrations not adversely affect the sound. The thought of putting electronics in the most highly resonant area of your system seems counterproductive.

The Amplifier
The amplifier is a dual-mono design. It uses a toroidal transformer with a split supply to each channel. It has an adjustable 12 db/octave crossover, with a range of 30 to 200 Hz. It puts out 150W RMS @8 ohms and 200W RMS @4 ohms. The technology of the amp is Class D half- bridge PWM, using this “cutting edge class D technology to accomplish its power transfer. The extremely low impedance of the amplifier over the low frequency range provides near perfect signal transfer to a non-resonate load. Stable and low impedance assures linearity of the signal transfer to the load through proper cabling.” It has controls for volume, phase, crossover point, subsonic filter and auto standby.  It can be used with a normal on/off or in an auto-standby mode. This mode automatically turns on amp if it detects a signal and turns amp off if signal is not detected for a period of time. It has input for both line level RCA and speaker level 5-way binding posts. The amp operates with either 120v or 240v with proper adaptor. The build quality of the amp seems very high for its price range. It looks good enough to go in the equipment rack with high-end equipment.

Setup was quite easy. I used a split output from my AV preamp subwoofer output to each of the RCA inputs. The amp is very versatile for its hookup to a preamp or another amp. You can also send front main RCA outs from a preamp to the amp, use its crossover and send RCA outs to your main amp. You can use second main outs from your preamp and send it the amp. If you have a second main out, and no sub out, this is what I would suggest using. Either way, you get stereo bass. Almost all sub outs are in mono. You can also use speaker outs from your main amp to the TBI, and use TBIs crossover to extract the bass. You then use the speaker out to go to your main speakers. The TBI amp will give a 6dB roll off below 70 Hz to your main speakers. This aids in taking low bass out off your main speakers, which may not comfortable with trying to reproduce real low frequencies.

One problem with bass is that most subwoofer outs of players and preamps sum the low bass to mono. Many recordings also have the low bass summed to mono. Bass distortion is one of the main reasons for muddiness in the sound of a system. Most speakers are not very happy with reproducing frequencies below 60 cycles for large speakers, or 70-80 cycles for small speakers. Many AV and multichannel systems may have three places where low-frequency crossovers are used. The player, the preamp and the subwoofer all have crossover points. Crossover points are not brick-wall drop offs, they change their output frequencies slowly according to the slope of the crossover. Care must be taken to balance out the crossover points of various components. Proper use of subwoofers can add clarity to all frequencies of a system. The subwoofer outs of the amp are used to connect to the subwoofers with speaker cable.

I do not have any other non-amplified subwoofers to use, so all my listening was done with the Magellan VIII SU subwoofers. The original TBI amp was serviceable and somewhat cheaply built. If you had two subs they sounded better using two separate amps even though one would drive both subs. One of the new stereo amps sounds better than using two of the older amps. The original TBI amps sounded very good, but putting in the MGD-200 definitely showed the short comings of the old amps. The sound with the new amp was more controlled and powerful. Even in feeling the air output at the port, the air movement seems, more controlled and stronger. On a 25 cycle test tone with the new amp caused something on the equipment rack behind it to vibrate, that the old amps did not do. With the new amp in the bass was more defined and controlled.  The bass was also more tonal. All frequency ranges of my system were improved by the reduction of slight muddiness in the bass. The systems sense of presence, clarity and dynamics were improved.

The TBI subwoofers are the only subwoofers I would use in a music system. They may not satisfy the listener who wants the room to shake and bass to sound like a rock concert bass. But if you like bass that sounds natural and blends with about any speaker system, the TBI might be for you. This amp is a definite upgrade for previous TBI sub owners. It is also a consideration for other passive subwoofer owners or builders.

Associated equipment
Heavily-modified Outlaw 950 multichannel preamp
Crown Macro Reference Amp
Oppo BD-83 SE disc player
Samsung BD-UP 5000 Blu-ray/HD DVD player
Modified Marantz DV 9500 SACD player
Eminent Technology LFT-8
AV-123 super tweeters (3)
Sumo, Parasound, and Adcom stereo surround amps
Optimus (Linaeum tweetered) and Chapman monitors for surround and center channel speakers
Miscellaneous Equipment: Tube trap; Shakti Onlines, Stones and Sonic Halographs; Brightstar isolation basses; Jena Labs and Cardes cables, isolation feet, lead bricks and sheets: and custom speaker cable risers.

— Clay Swartz

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