I'd like to thank everyone who has taken the time to answer my question
about the manufacturer of the CA810. My intention was to use this amplifier
as a substitute of one that I am suing right now: the LM759. Let me tell you
quickly about my situation.
          I am performing an experiment that deals with sinusoidal signals
from 1
to 15 Khz. To start, I fed 1Khz to an LM759 power amplifier, and then the
output of the amplifier is fed to a set of earphones. Here is the problem:
When I monitor the signal without the earphones, I get a nice sinusoide of
about 6Vpeak, but when I hook up the earphones, the signal goes down to
about 0.9Vpeak. From here, if I try to raise the gain, the signal gets
distorted. The rest of the experiment conists on having a microphone pick up
the audible tone from the earphones and feed it to a digital signal analyzer
to check that the signal is not distorted. What's my problem? It looks to me
that the earphones are loading the amplifier big time, but why should that
happen, since even the data sheets show examples with speakers connected
directly to the power amplifier? I was thinking about using an audio
transformer to isolate the earphones from the output of the amplifier. Any
thoughts or pointers? Best wishes.