Product Review -
Carver Premiere AV-705x Five Channel Power Amplifier - April,
1997
By John E. Johnson, Jr.
Click to see larger photo |
Carver Premiere AV-705x Five Channel
Power Amplifier; Home theater amplifier; Five channels of
amplification; THX Certified; 125 watts rms/ch into 8 Ohms, all
channels driven, 20 Hz - 20 kHz; Frequency response 20 Hz - 20
kHz + 0 - 0.2 dB; Input impedance 50 kOhms; Damping factor 200;
Sensitivity 1.0V rms for 100 w/ch output into 8 Ohms; THD
<0.03%; Rise time 2.2 µsec; Size 5 3/4"H x 19"W x
19"D; Weight 42 pounds; Black sheet metal; $1,199; Carver
Corporation, P.O. Box 1237, Lynnwood, Washington 98046-1237;
Phone 206-670-3424; Fax 206-778-9453; E-Mail [email protected].
The Carver AV-806x Multi-Channel Amplifier was a six channel amp
for home theater that won considerable accolades from the audio
press last year. The only problem with six-channel amps - and
there are several of these on the market - is that you only need
five channels. The sixth was designed in anticipation of using it
with an unpowered subwoofer. Probably 99% of the subs out there
now are self-powered, so the sixth channel is not needed by most
of us. Enter the AV-705x, which is Carver's latest design for
home theater amplification.
The 705 uses totally modular circuitry, with each amplifier being
a PCB that is inserted front to back, like accessory boards in
computers [click here to see photo of inside of amp]. The front of the PCB has ten pins that connect to
the power supply, and the back has the input RCA jack and one
pair of three-way speaker binding posts attached. The jack and
binding posts protrude from the back of the amplifier [click here to see
photo of back], along with a small
potentiometer post. The potentiometer controls the volume of each
amplifier section. For THX use, the pots are turned all the way
clockwise. We would like to see five-way binding posts that will
accept heavy spade lugs. The posts on the 705 will accept pins,
bare wire, and banana plugs. Each channel is marked on the back
in BIG numbers, 1 - 5. Someone up there in Lynnwood has eyesight
about like mine!
The class A input voltage amplification stage has a servo circuit
preceding it which eliminates DC from entering the circuit. This
is followed by a two stage driver, which interfaces with the
output stage (four bipolar devices per channel) where current is
made available to the output (speakers). A small amount of
negative feedback has been employed for the purpose of optimizing
every amp module for consistency rather than to remove
significant amounts of distortion. What makes the circuit
interesting is that there are no point-to-point wires in the
amplifier stages. Everything is on one PCB for minimal signal
path, for easy repair, and low cost to the consumer [click here to see
photo of amplifier module PCB].
This is a change from the AV-806x which was a less refined first
pass at a modular approach. The 705x uses new advanced topology
and is all discrete, whereas the 806x was a chip driver based
design with narrow open loop bandwidth, output inductors, and
less safe operating area.
Some of the new Carver designs use their latest power supply
technology, called "Magnified Current Amplification."
This allows the output section to deliver high voltage when
necessary, or high current. The older designs used "Magnetic
Field" technology, which allowed only high voltage. Both
designs are class H, in that the rail voltage is variable, making
the amplifier very efficient and cool-running. Class H is a
little slower than class A/B in transient dynamics, but this is a
subtle thing that is unlikely to be noticed under average
listening conditions. The AV-705x has a conventional,
large-device-based, high safe operating area (SOA) output stage
(600 watts of SOA per channel) to get high current by using four
output devices (the same devices as used in the Lightstar).
Carver reserves the Magnified Current design for their >200
watts per channel power amps where it is harder to achieve high
current and voltage capability with conventional designs. The 705
operates in class A/B.
We tested the 705 for dynamics by using a recording of a bass
guitar that was plucked. The initial attack requires good
dynamics to reproduce it, and the 705 is excellent in this
regard. Square wave response at 10 kHz and ± 10 V shows a
relatively fast, clean waveform [click here to
see photo]. The Carver Lightstar
uses only two output devices per channel (350 w/ch), while the
705 uses four (125 w/ch). However, the Lightstar power supply is
much more sophisticated. To make up for this difference, the 705
has the ability to supply additional power to the particular
modules that demand it at any one time ("Power
Steering"). This is usually the center channel, where about
75% of the sound is going anyway, but it can be any channel, and
the power steering allows 200 watts to any one module at any one
time. While the AV-806 had 133 w/ch, the AV-705, at 125 w/ch can
deliver more power into real loads, particularly surround sound.
The 806 had individual power capacitors for each channel, and the
AV-705 has two centralized Philips 25,000 µF, 75 V power
capacitors as well as a huge EI core transformer. Energy storage
for the 705 is 109 Joules. This centralized energy storage allows
for the Power Steering mentioned above. The 705 also uses
"Total Direct Coupling" that provides constant output
impedance (constant damping factor) out past 20 kHz. This
maintains high frequency neutrality (sonically) regardless of the
loudspeaker load.
In conjunction with the 705, we used a Toshiba 2006 DVD Player,
Yamaha 990 Receiver, Yamaha DDP-1 AC-3 Decoder, Millennium DTS
Decoder, McCormack CD Transport, Audio Alchemy CD Transport,
AudioQuest Cables, Nordost Flatline Cables, Eminent Technology
Speakers, and Krix Speakers.
One of the first things we noticed was that the 705 has much less
hum than most other home theater (multi-channel) amplifiers we
have tested. We use a large number of components, with wires
going everywhere, so if any piece of equipment is subject to
ground loop hum, it shows up. It is not something we complain
about, because the lab is a ground loop hum paradise . . . a fact
of life for a test facility. The 705 had almost no hum at all,
suggestive of very good design in the noise department. Maybe the
Carver design/test lab has lots of wires everywhere too. Front
panel red LEDs come on when the unit is powered up (rocker
switch), then after a few seconds, solenoids switch in (to
prevent power-on thump), and the LEDs extinguish. The solenoids
switch in again at power-off, to prevent thump, and the red LEDs
slowly dim as the power capacitors discharge.
DVD movies use Dolby Digital (DD or AC-3) sound, which is full
range in all five channels. "Lethal Weapon" was first
on the list. This movie has plenty of firepower in the sound
department, and the 705 was up to the challenge with crisp, clean
sound, loud enough for any aficionado. "The Glimmer
Man" is a modern, lots-of-explosions, but not-much-story,
movie. It allowed us to pay attention to the picture and sound
quality, without being distracted by anything interesting
happening in the film. Again, the 705 pulled it off without a
hitch. While "Lethal Weapon" was a bit bright . . . not
harsh, just a little forward in the treble . . . "The
Glimmer Man" was right on, indicating that movie sound
tracks are a big variable, but the AV-705 reproduces them
accurately, whether they are good or bad. "Courage Under
Fire" has some outstanding special effects that rocked the
room. No clipping could be heard. This amp just goes and goes. We
cranked it up to levels just short of obscene, and the Carver
maintained its composure. Large-scale sound effects can't carry a
movie any more, but at least they keep you awake. Regular CDs and
DTS CDs also gave us a very nice surround envelope. One DTS CD is
a big thunderstorm, and those lightning bolts need lots of room
in the amplifier power supply. No problem. There is no shortage
of kick with the AV-705. The power steering is obviously at work
here. The DTS demo disc (published by DTS) has the most demanding
sound tracks we have ever found, and the 705 did not clip
(audibly) once!
THX certification requires that the power amplifier be used with
no attenuation at the inputs. The 705 has small potentiometers
for each amp module (no individual volume control pots on the
806), and the instruction manual states that, for THX operation,
they are to be turned fully clockwise. For non-THX operation, we
found a great use for the pots. We turned them all down about 20%
and then set our balance controls on the receiver to 75 for all
channels. Then we used the pink noise test tone through each
channel and adjusted the pots so equal volume was perceived at
the listening position. This equalized for the fact that the room
is not completely sonic-symmetrical (furniture, walls, window,
doorway, etc.). This made it much simpler to use the numerical
status on the balance control from the Yamaha receiver for fine
tuning each movie, since it was now completely pink-noise
balanced at a readout of 75 for all channels (notwithstanding the
lack of deep bass in the center and rear surrounds). The 705 is
one of a few multi-channel amps with volume controls for each
channel. Very handy feature!
In summary, the Carver AV-705x Five Channel Amplifier has great
sound and dynamics, low hum, adjustments for each channel volume,
and is priced right. We consider it to be one of the best buys in
home theater amplification.
John E. Johnson, Jr
© Copyright 1995, 1996, 1997
Secrets of Home Theater & High Fidelity
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