Intermodulation Distortion, or I.M. is characterized
by the appearance in the output waveform of fre-
quencies that are equal to sums and differences of
integral multiples of two or more of the frequencies
present in the input signal. The difference between inter-
modulation distortion and harmonic distortion is that
two or more different frequencies must be present to
produce intermodulation distortion (only one frequency
is needed for harmonic distortion to appear), and that
intermodulation distortion products may not be
harmonically related to the original frequencies. Like its
harmonic distortion figure, the intermodulation dis-
tortion in the P-2200 is low enough to be virtually
inaudible even in the most critical situations.
Dynamic Frequency Response Shift is related to both
harmonic and intermodulation distortion. When high-level
low and high frequency signals are present in the same
waveform, the high frequency signals "ride" on top of the
low frequency waveforms (see Figure 65, Page SEVEN 1 ) .
If amplifier headroom is inadequate, the low frequencies
may "push" the high frequencies above the output limits
of the amplifier, clipping them off the waveform (Figure
65C). The low frequencies may remain unaltered, but the
high frequencies are severely reduced. At the same time,
harmonics of the high frequencies are produced which
add to the super high frequency content of the signal.
Thus, along with the distortion created by the clipping,
the frequency response of the original signal is drastically
altered. This type of distortion can be reduced by in-
creasing system headroom (using a more powerful
amplifier like the P-2200), and by biamplifying the
system as discussed on Page SEVEN 1 .
The extremely low distortion figures of the P-2200
indicate its overall quality and mean that its sound will
be precise and natural.
FREQUENCY RESPONSE (Refer to Figures 5 & 16)
The frequency response of the P-2200 describes the
variation in its output signal level with frequency when
the input signal is held constant. The extremely "flat"
frequency response curve of the P-2200 is an indication
of its overall quality and its ability to respond to upper
and lower harmonics of signals all the way to the
extremes of the audio spectrum.
Because extreme stability is necessary for some types
of commercial sound applications, notably 70-volt lines
(see Page SEVEN 1 1 ) , some manufacturers restrict fre-
quency response or allow relatively high distortion in
return for increased amplifier stability. The P-2200, on
the other hand, has excellent frequency response and
ultra-low distortion, yet is inherently stable under the
most difficult loads, even in the "mono" mode.
The frequency response of the P-2200 has been
intentionally limited, however, at very low frequencies
(sub-audio). Because of this, severe low frequency
transients, or DC offset, appearing at the input to the
P-2200 are unlikely to damage a speaker load. Other
amplifiers which are DC coupled throughout may have a
"flatter" sub-audio frequency response, but this makes
them capable of amplifying dangerous DC input voltage
or sub-audio transients and delivering them (at high
power) to a speaker.
OFFSET VOLTAGE
This specification indicates the amount of DC voltage
naturally present at the output of the amplifier. A high
DC voltage could damage the loudspeaker load; the
±10mV ( 1 0 one-thousandths of a volt) level from the
P-2200 is insignificant.
UNIT STEP FUNCTION RESPONSE (Refer to Figure 27)
A unit step function is like the leading edge of a
square wave; it goes up, but never comes down. The
response to this input indicates the output of the P-2200
for a DC input signal which might come from a faulty
direct coupled preamplifier or mixer. Note that the
P-2200 will not reproduce a DC voltage fed to its input,
thus adding an extra measure of loudspeaker protection.
POWER BANDWIDTH (Refer to Figures 3 & 14)
The power bandwidth of the P-2200 is a measure of
its ability to produce high power output over a wide
frequency range. The limits of the power bandwidth are
those points where the P-2200 can only produce 1 / 2 the
power that it can produce at 1000Hz. While the
frequency response is measured at relatively low power
output (1 watt), the power bandwidth is measured at the
P-2200's full power output (before clipping). The power
bandwidth of the P-2200 is quite "flat," and extends to
200kHz, well beyond the limits of the audio spectrum.
The wide power bandwidth of the P-2200 means that
it can reproduce high level upper harmonics of a signal
as easily as it can reproduce mid-range fundamentals. It
means that you get full power performance from the
P-2200 over the entire audio frequency spectrum. This is
especially important when the amplifier is called upon
to reproduce musical material with high energy over a
wide frequency range, such as rock and roll.
PHASE RESPONSE (Refer to Figure 11)
The phase response of the P-2200 is a measure of the
amount of time delay it adds to different frequencies.
An amplifier with perfect phase response would introduce
equal time delay at all frequencies reproduced. The
P-2200's worst case phase shift of -10 degrees at 20kHz
corresponds to a 1.4 microsecond (1.4 millionths of a
second) delay period which is insignificant in even the
most critical audio applications.
Fig. 29 - Waveform of Amplifier with Poor Phase Response.
An amplifier with poor phase response would change
the shape of a waveform that was made up of a funda-
mental frequency and several harmonics by delaying
each harmonic differently. The effect might be similar
to that shown in Figure 29.
CHANNEL SEPARATION (Refer to Figure 10)
This specification indicates the output from one
channel when a signal is fed to the other channel. The
P-2200's channel separation is very good, which means
that even critical stereo programs will be unaffected by
crosstalk between channels.
