Hifonics XX-Goliath- Amplifier Review

Nevermind the Underdog - It's all about the Giant

While discussing the amps for our Biggest, Baddest Amplifier Series and going through our archives, we reviewed this test report from a while back of the 5,000 amp from Hifonics you see here. Tech guru Garry Springgay tested the, well, Goliath (if the name fits). Though it's no longer made, some retail stores may still carry the product. (I mean, how many of these can you sell when they used to list for $5,000?!) You'll see it a lot cheaper now. Worth considering perhaps for someone looking to make a statement, and willing to follow Garry's advice to buy an amp with more than enough power so you don't have to push a product to its limits, causing it to overheat and perform inefficiently. This amp may not have made the cut for our series, but it's definitely a contender. —Ben Oh



Circuit Design
The Goliath is a Class D amplifier, in the traditional sense. That is to say, it is bandwidth limited and designed to be used only for subwoofer applications. A look inside confirmed my suspicions about the weight. This amp is built for some serious current flow. In addition to the two pairs of power connectors, the amp uses large heavy-duty buss bars to distribute the current to the board. The type of PCB is very good quality, double-sided, plated through and glass epoxy, which resists heat and vibration extremely well. This is a good thing because a powerhouse like this can generate plenty of both. On the main PCB, all of the parts are the through-hole variety, but all are high quality, low tolerance 5% or better. There are surface mount parts on the two daughter boards, used for power supply control and the Class D controllers.



At the power supply input there is a large "cap farm" with 24V to 35V 1,200uF caps for an input capacitance of 28,800uF. The power supply switching is handled by no less than 20 large TO-247 case-size Mosfets, switching the inputs of two very large toroids at about 25kHz. The energy output of the toroids is stabilized and stored in another huge capacitor farm, this time using 20V to 200V 1,200uF caps, for a total secondary capacitance of 24,000uF.

On the signal side of things, I was pleased to see high-quality, low-tolerance parts used throughout the input stages, and even though this is a bandwidth-limited amplifier, the caps in the circuitry were very good and easily could have been used in a good full-range amp. A lot of manufacturers cut some corners here, but not in the Goliath. Nice.



The stereo input signal is summed to a mono signal and passed through the gain section, an adjustable 15Hz to 36Hz -24dB subsonic filter and teh -24dB crossover, which can be set anywhere between 15Hz to 250Hz. Then it goes through an adjustable phase control which has the ability to provide 144 degrees of adjustment at 100Hz. The last stage of signal control before it's passed on to the amplification stage is a 0 to +18dB EQ circuit which can provide as much as 18.5dB of boost at 45Hz. The amp comes with a remote mounted box that provides control of the EQ circuit from the driver's seat.

Amplification is handled by 24 large Mosfets with a modulation frequency of about 118kHz. These TO-247 case devices leave no doubt as to the current capability of the Goliath. The output signal is extensively filtered with four large toroids and another set of capacitors and sent to the output terminals by a pair or relays, each capable of switching 30 amps of current. The signal travels from about mid-point on the board through a pari of 8-gauge cables. In an amp that has evidently had a lot of care and attention paid to the PCB layout and parts selection, these cables were strangely routed adjacent to the toroid and switching devices, allowing noise to be radiated back into them. Now I realize that these devices are switching at ultrasonic frequencies and the amp will be hooked to a woofer, but the noise does show up on the test bench,e ven with extensive pre-filtering applied. Can you hear it? Probably not, but it is there. I'll let you decide if it matters to you.

Performance
When i began to measure power levels, I found the power at 1.0% THD+N was a little lower than quoted in the specs. After double-checking all my measurements, I realized that Hifonics does not qualify their power figures with a distortion limit. By letting the amp run a little into clipping, I could get the claimed power from it, but at distortion levels around 2%-5%. At no point during the power testing did the amp complain or show any sign of stress—it simply kept cranking out gobs of power.



I ran frequency response plots and found the response of the Goliath to be within 1.0dB from 18Hz to 195Hz. These limits are caused by the amps filter features: The subsonic limits the low end and the crossover controls the roll-off at higher frequencies.

As you'd expect with a Class D amp, the slew rate, damping factor and S/N ratio are not exceptional, although still decent for this topology. I measured a slew rate of just over 2.5V/uS and damping factor was high for a Class D amp at 157.5. Idle current was pretty high at 8 amps, but considering the amount of devices in this giant, not out of line at all. when you put a 5,000-watt amp in your trunk, you're probably not too concerned with overall system efficiency. With the Goliath, it seems you can have your cake and eat at least some of it, too. At full power into 1 ohm, it was an average 70%, but at full power into 2 ohms, it jumped to 82%. That's a really good number from such a large amplifier.

There is a lesson here for all you bass heads. Buy an amp large enough to give you the power you need without having to push it to its design limits and you'll be rewarded with a cooler running, better sounding, more efficient system.



I did notice that it took about two seconds for the amp to stop playing after I removed the remote turn-on voltage, not a problem in and of itself, but it could cause a turn-off noise in your system if you have a source upstream that shuts off before the amp. On the bench, the amp exhibited no turn-on or turn-off noise.

Manual
The Goliath comes with a 12-page full-size manual, covering all of the Generation XX amplifiers. It gave me all the info I needed - the text and accompanying drawings explained the features and controls fairly well. There are two pages devoted to system design and setup, and a very simplified page for troubleshooting various problems. Another page allows you to compare all the specs of the Generation XX amps and look up the specifics of the one you bought. All in all, it's a pretty adequate manual that covers most issues you'd encounter during install and setup. It includes warranty info and tells you how to contact Maxxsonics, the parent company.

Listening
When it comes to evaluating the sound quality of a Class D subwoofer amplifier, many learned folks would tell you they all sound the same: bad. I don't necessarily agree with that opinion. I've got a favorite subwoofer system that I've listened to for thousands of hours and know very well. Using a couple dozen of my favorite tracks, I can readily pick out something that's "different" in my subwoofer system. I hooked up the Goliath to the system and settled in for a couple hours listening to some of my favorite tracks for evaluation of the bottom end.

Not surprisingly, the Goliath showed that it had a ton of headroom in the power department, and easily handled most tracks. Power-hungry, very dynamic tracks like the Atlanta Symphony Orchestra's "Fanfare for the Common Man" and The California Projects' "I Get Around" were also handled without any signs of stress. This kind of power on your subs can be addicting.

Listening carefully to Level 42's "Physical Presence" and Don Dorsey's "Toccata in D Minor," I thought the amp lacked a bit of speed in handling the dynamics of either the synthesizer or Dorsey's pipe organ. I also noticed a bit of rolled-off response in the extreme bottom end when listening to Avril Lavigne's "Sk8er Boi." I'll admit here to usually using an amp that is flat down to 5Hz, so I think what I heard was the effect of the previously mentioned subsonic filter. Other than those small foibles, the Goliath sounded controlled and ultra strong.

Conclusion
The Hifonics XX-Goliath from the folks at Maxxsonics does what you'd expect, and more. It offers good control features, the ability to add a second Goliath as a slave unit (those poor woofers!), and is a high-quality, well-built amplifier. Its prodigious power has to be experienced. There is nothing like having thousands of watts on your car's subs. Even if you don't usually "crank it," the additional headroom is there and you'll notice it. At about $5,000, this amp is not cheap, but this is an area where spending a little more dough pays off.

TEST RESULTS OUTPUT POWER @ 1%THD, 100Hz, 14.4 Volts
Mono @ 4 ohms	1,708 watts
Mono @ 2 ohms	3,062 watts
Mono @ 1 ohm	4,696 watts
OUTPUT POWER @ 1%THD, 100Hz, 12.5 VOLTS
Mono @ 4 ohms	1,237 watts
Mono @ 2 ohms	2,223 watts
Mono @ 1 ohm	3,512 watts
Distortion at rated power, 100Hz, 14.4 volts 0.1% @ any impedance
Input sensitivity	216mV to 9.0 volts
Frequency response (+1dB)	18Hz – 195Hz
S/N ratio (A weighted, below clipping, min gain)	-78.3dBA
Slew rate	2.52V/µS
Damping Factor @ 100Hz, 4 ohms	157.5
Idle current	8.0 amps
Maximum current consumption, unclipped	465 amps @ 4,696 watts
Efficiency at 1/3 power, lowest impedance	71%
Efficiency at full power, 1% THD, lowest impedance	70%
Crossover slope	24dB/octave
Crossover range, lowpass	15Hz - 250Hz
Low-frequency boost	+18.5dB @ 45Hz
Dimensions	28” (711mm)L x 11.2” (285mm) W x 2.6” (66mm)H

Photography by Paul Morton