THX-Ultra Five-Channel Power Amplifier
Parasound
amplifiers have received much attention over the years primarily because John
Curl has been a key designer of their flagship models. Mr. Curl's reputation in
the area of power amplifier design has been highly regarded in the audio industry.
One such design is Parasound's HCA-2205AT, which is a five channel THX-Ultra certified
amplifier. This multi-channel amplifier has the ability to drive difficult loads
while still providing enough current to easily meet the THX-Ultra requirements.
The signal path has no capacitors or inductors to degrade the sound. In addition,
the amplifier is designed to operate in a high-bias Class A/AB mode to minimize
crossover distortion. The massive toroid power transformer has independent secondary
windings for each channel. A total of 150,000 uF of capacitance is used to store
the large power reserves that supply the output transistors. The design uses hand
matched complementary JFET devices for the input stages, MOSFETs for the driver
stages and a total of forty beta-matched, 15 amp bipolar transistors on the output
stages. That's eight dedicated high-current bipolar transistors for each channel.
Heatsinks cover both sides of the unit and a good portion of the rear panel providing
completely conventional cooling without the need of a noisy fan. As a result,
the amplifier is capable of driving five channels with 220 Watts per channel into
8 ohms or five channels at 300 Watts per channel into 4 ohms. The front panel
indicators provide status including AC Present, Standby/Normal Operation,
Current Overload and Over Temperature conditions.Construction
Conventional linear amplifiers have always been somewhat judged by their weight.
After all, linear high current designs require large power transformers for continuous
power needs as well as large capacitors to hold huge power reserves for peak transients.
In addition, when you add five channels to the unit, you're talking about some
serious weight. As expected, the HCA-2205AT is a back-breaker at a hefty 85 pounds.
The build quality of the amplifier is impressive and far better than many amplifiers
we've seen in this class. Given a list price of less than $2000, we were surprised
to see this level of build quality. Handles located on both the front and back
are essential when moving the unit around. The front panel is made from a hefty
chunk of aluminum and large heat sinks occupy most of the outer perimeter of this
well made chassis.
The
rear panel of the HCA-2205AT has the two additional handles that help distribute
the weight during a move. The left side has five gold-plated unbalanced RCA connectors
for each channel. In addition, level controls are provided for adjusting the sensitivity
of each input independently. A THX reference mark is indicated for setting the
proper THX reference level. There's also a 12 volt trigger input that we used
with our Parasound AVC-2500u to remotely turn on the power amplifier. The center
of the back panel is largely taken up by one of the three massive heat sinks.
The right side of the rear panel holds the five pairs of speaker outputs on gold-plated
5-way binding posts. The detachable heavy gauge power cord plugs into the unit
just below the speaker terminals.
Setup
The
Parasound AVC-2500u was used to drive the HCA-2205AT amplifier. Six UltraLink
Platinum Ultima Mk II cables provided the link to the amplifier. The HCA-2205AT
drove our three M&K THX-Ultra certified S-150THX front channel speakers and
two rear SS-250 Tripole® surrounds. A pair of M&K MX-350 MkII THX-Ultra
subwoofers was used to handle the low-end with their built-in 350 Watt amplifiers.
All main and surround speakers are rated at 4 ohms and require a substantial amount
of current to drive them at high levels. The huge 2kVA toroid power transformer,
large filter capacitors, and 8 output transistors per channel are the main reason
why this amplifier had no problem pushing large amounts of current into these
low impedance loads.
Performance
We
tried a variety of source material with this amplifier including our high resolution
multi-channel SACDs and DVD-Audio discs. There are also plenty of high-impact
movies with Dolby Digital and DTS 5.1 audio. Our system is currently using a THX
processor and an M&K BMC mini 5.1 bass management unit for the analog 5.1
inputs, so the main speakers have a crossover frequency set at 80 Hertz. Therefore,
the amplifier was spared the task of driving our main speakers below this frequency.
One
of our favorite 5.1 surround mixes is a track called Fire from the Studio
Voodoo release. The aggressive African-style compilation features Swahili
voices in various channels along with a gradual increase in volume and makes for
a wonderful test track. In addition, when things get warmed up, a deep descending
bass exercises the transition between the main speakers and the LFE (low frequency
effects) channel. This artistic piece is highly recommended for 5.1 surround enthusiasts.
Another interesting recording on DVD-Audio is the multi-channel 24/96 Brazilian
Jazz disc in the MLP format. This high resolution, percussive mix is a real
treat and certainly exercises the dynamics of your surround system. The sonic
attributes of the HCA-2205AT were that of a high-end amplifier. The wide soundstage
impressed us along with the pinpoint imaging between channels. The sound was neutral
and free of harshness while still providing plenty of power to our speaker system.
Our M&K S-150THX main speakers
and SS-250 surrounds are not easy to drive for most amplifiers. In fact, with
our system a total of 33 individual drivers (15 in the three S-150's and 18 in
the pair of SS-250's) can be running at any given time and that's not including
the subwoofers. This requires a huge amount of power and the HCA-2205AT handled
it with ease. The amplifier never showed any signs of being strained, even at
very high levels. We have had this amplifier in our system for nearly six months
and it has performed flawlessly while still sounding wonderfully open and smooth.
-
Kevin Nakano