Specifications

provided for reactive loads.
To Sum It All Up
The points we've tried to make are
relatively few, but they spell the differ-
ence between a McIntosh output-
transformer equipped amplifier and
every other kind of amplifier around.
1. A transformer equipped ampli-
fier will deliver rated power at any im-
pedance for which a transformer tap
is provided.
2. An OTL amplifier designed for
8-ohm operation cannot operate safely
(according to the FTC rules) when
driving lower impedances (4 ohms,
2 ohms, etc.), yet such loads common-
ly occur either because of speaker im-
pedance variations with frequency or
because of paralleling of multiple
speaker systems across one channel
of an amplifier.
3. The new FTC power rule regard-
ing audio amplifiers has forced many
manufacturers to omit 4-ohm ratings -
even though 4-ohm speakers arc in
common use. McIntosh transformer-
equipped audio amplifiers deliver full
power at any impedance for which a
transformer output tap is provided.
4. Because of their design, McIntosh
transformers introduce less series leak-
age inductance than is commonly en-
countered with OTL amplifiers which
require a series inductance between
the output circuit and the speaker con-
nection for amplifier stability. At the
8 ohm tap of our MC 2205, leakage in-
ductance is a low 3.5 microhenries.
This represents an impedance of only
2.2 ohms at a frequency of 100 kHz.
5. Properly designed output trans-
formers impose no limitations on fre-
quency response. At the 8-ohm tap of
the MC 2205, response is down 0.3 dB
at 50 kHz. With a 4-ohm toad con-
nected, response is down 0.1 dB at
50 kHz.
6. Phase response of the MC 2205
amplifier, using its specially designed
output transformer, is accurate to
within 9 degrees at the 8 ohm tap at
a frequency of 50 kHz and undergoes
zero degrees of phase shift at 20 Hz.
At the 4-ohm tap, phase shift at 50 kHz
is only 7.2 degrees.
Next time anyone gets into an argu-
ment with you concerning the attri-
butes of an OTL amplifier versus a
McIntosh transformer-equipped ampli-
fier, you might let your adversary read
this story.
Output volts
Fig. 12 — Load and limiting data of
a non McIntosh high-powered transformerless amplifier measured at 8 ohms output.
12
fiers. In Fig. 10 we have combined the
safe operating diagram of Fig. 10 with
load and limiting characteristics at the
8-ohm tap of our MC 2205. As you
can see, even when the load is totally
reactive, every possible voltage and
current condition falls within the
safe operating area of the output de-
vices used. Compare this diagram with
Fig. 12 derived from data concerning
the output transistors used in a cur-
rently available high-powered amplifier.
Note that inadequate protection is
Fig. 11 - Current versus voltage
limitation epibase type
output transistor
Collector volts