[net.audio] Equipment Review: NAD 2200

mwm@ucbtopaz.CC.Berkeley.ARPA (Praiser of Bob) (05/14/85)

[What's abelian and sounds great?]

The addendum first. In an earlier review, I said that the AR System
Remote Control was inaudible. Having just put in a better amp, I have to
retract that statement. If you are listening to a quiet passage with
much amplification, then the SRC adds a gentle "pop" to the music when
the IR receiver kicks on. Since it only happens when you are changing
the control settings, I still think the SRC is a worthwhile box.

Now, on to the NAD.


Appearance and Features:


The NAD 2200 ("PowerTracker", for some reason) costs ~$450. It's a 100
W/ch amp that comes in a black aluminum cabinet measuring 42x12.3x37 cm,
weighing 12.5 kgs. The front of the box has a power switch and green
power led on the left, and a trio of led's in the center. The top led is
red, and goes on when the amp decided that it's clipping. The second led
is also red, and indicates that the amp has disconnected itself from the
output for some reason. The final led is yellow, and is on when you have
the NAD "soft clipping" enabled.

When it comes on, the amp goes into protection mode (disconnecting the
output lines) long enough to insure that it's transients have settled.
This same feature comes on when it thinks it's being driven to
overheating (trying to draw 200+ watts for a couple of seconds). The
"soft clipping" causes the amp to lower the gain as it approaches
clipping levels. A nice feature if you like to drive your amp very loud.
I haven't turned it on, and have been told that the circuitry should be
physically removed from the amp.

The amp can be bridged, giving you a mono 400 W amp. The speakers posts
on the back are color-coded for this, meaning that the negative post of
the left channel is black instead of red. For fans of DC-light amps,
there is a "lab in" that avoids the amps signal filtering (details
later).


Amp design and specs:


The 2200 uses a couple of rather radical (to me, anyway) design
technics. It's billed as a "commutating" A/B amp, meaning that there is
a class A amp for low level use. When the higher power levels are
needed, it switches a second A/B amp into the circuit. The second amp
can deliver 500 W peak power. Note that this amp is added to the
circuit; the low-power amp stays in circuit to prevent switching noise.

The second radical feature is bass inversion in the right channel. The
bass signal in that channel is inverted, amplified, then inverted again
before it's output. This results in the bass drawing power out of phase
with itself, so it needs less power - or, so you can get better bass
with the same amount of power.

The specs on all this are:

Power:	100 W				THD	0.03%
IM distortion (both SMPTE and IHF): <0.03%
Clips at: 140W (8 Ohms), 200W (4 Ohms)	IHF headroom: +6db (8 ohms)
IHF dynamic power: 400W (8 Ohms), 600W (4 Ohms), 800W (2 Ohms)
Slew factor: > 50			Slew rate: > 35V/usec
Damping:	100
Freq response, LAB input: 3Hz to 80kHz, +0, -3dB
Infrasonic Filter, Normal input: -3dB at 15Hz, 12dB/octave
Ultrasonic Filter, Normal input: -3db at 40kHz, 12 dB/octave


How it sounds:


The bottom line on the specs and techno-magic is, of course, how the amp
sounds. A one-word description of the amp is "smooth." When running at
normal levels (for me, that is), the amp doesn't seem to be working at
all, just delivering sound. Even when driven to clipping, it doesn't
sound like it's struggling.

The next thing I noticed about the amp was the bass. It's very precise,
without sounding peaky. If this is due to the inversion in the right
channel, I expect it to appear in many amps in the future.

After the bass, the clarity of the midrange comes to the fore (much to
the detriment of my tuner :-). The image is large and stable, but will
need some help with center fill. All in all, a very good sounding amp.

[The rest of the system used: Magnavox FD 1000 CD player, Nak BX-100
cassette deck with unknown dbx unit (borrowed for the occasion)
AR SRC subbing for a preamp, a pair of ITC 1 speakers, and a pair of
little-known Canadian speakers (borrowed with the Nak), KimberCable
speaker cable and Gold-Ens interconnects.]


Summary:


An excellent buy. When compared to amps that cost twice as much
(Bryston, Tanberg), the 2200 is a clear winner - especially the clarity
in the midrange. With amps in the same price range (Carver, Haffler),
there isn't any contest. The 2200 sounds more natural, and better on all
points.

If you're looking for an amp in the < $1000 price range, you'll be doing
yourself a disservice if you don't give this amp a listen.

	<mike

dmmartindale@watcgl.UUCP (Dave Martindale) (05/18/85)

I'd be very surprised if the amplifier inverted only the low frequencies
in one channel.  More likely, it inverts the channel entirely, and then
"re-inverts" the signal simply by reversing the colour coding of the
speaker binding posts on that channel.  This does cause the two
channels to load the power supply primarily out-of-phase, allowing the use
of a smaller power supply for the same output power (clever) and also
means that bridging the amp for mono requires nothing more than connecting
both channels' inputs together.

Unfortunately, it must mean that the amp is incompatible with headphones
or anything else that requires a common speaker ground.

ben@moncol.UUCP (Bennett Broder) (05/18/85)

>The second radical feature is bass inversion in the right channel. The
>bass signal in that channel is inverted, amplified, then inverted again
>before it's output. This results in the bass drawing power out of phase
>with itself, so it needs less power - or, so you can get better bass
>with the same amount of power.

Sorry, but this feature is neither new nor radical.  It has been used
in high powered tube equipment for years.  Actually, I assume that the
*entire* right channel is phase inverted.  A circuit that only
inverted the bass would be a sonic nightmare.

mwm@ucbtopaz.CC.Berkeley.ARPA (Mike (I'll be mellow when I'm dead) Meyer) (05/21/85)

In article <1859@watcgl.UUCP> dmmartindale@watcgl.UUCP (Dave Martindale) writes:
>I'd be very surprised if the amplifier inverted only the low frequencies
>in one channel.  More likely, it inverts the channel entirely, and then
>"re-inverts" the signal simply by reversing the colour coding of the
>speaker binding posts on that channel.  This does cause the two
>channels to load the power supply primarily out-of-phase, allowing the use
>of a smaller power supply for the same output power (clever) and also
>means that bridging the amp for mono requires nothing more than connecting
>both channels' inputs together.

On closer reading, you're right. However, they leave the colour coding
alone, and relabel the +/- posts on one channel.

>Unfortunately, it must mean that the amp is incompatible with headphones
>or anything else that requires a common speaker ground.

Yup. In nice, bold letters above the diagrams in the owners manual it
says "Caution: do not connect the output of this amplifier to any ...
device that uses a common ground for left and right channels."

However, at the price/performance ratio of the 2200, I'll live with it.

	<mike