Index to Articles

 

Product Review - Carver Premiere AV-705x Five Channel Power Amplifier - April, 1997

By John E. Johnson, Jr.

Divider

Carver AV-705 Amplifier
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 custservice@carver.com.

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
Return to Table of Contents for this
Issue.