Hello again,
The hum is present even when the system consists solely of the HA-1,
a headphone plugged into the 1/4 inch jack, and the 120V AC power
cord plugged into a power source. I did try various power receptacles
throughout the house and turning off appliances, lights, ceiling fans,
air conditioners, etc. Also tried various power conditioning strips.
Some which are audiophile specific. Though, unfortunately, none
are designed to alleviate any DC bias that might be present in the
AC source.
With no input cables connected, switching through the various input
sources, both analog and digital, all produce identically the same hum.
The level of the hum does not depend on the input source, the volume
setting, or the normal/high gain setting. Only Mute and power down
stops the hum. In fact, Mute is the perfect way to AB it.
Again, it is very low level. Even the noise floor of most recordings
are decibels above, thus rendering it transparent. But with the rarest
of exceptions, I can only hear it when the music stops (or no source
at all when testing). Even silent passages within a playback of a
music file produce noise that masks the hum. That last sentence is
not always true, just generally true. There are some silent passages
in which I can hear the hum, though rare and barely perceptible.
My problem is that I'm within only a couple of days of the 30 day
return policy ending. Perhaps statements like the following are
misleading and setting the wrong expectation in my mind. The
following is from a review at hometheaterhifi.com.
"I could only detect absolute silence, when music was not playing
(in between music tracks) with the HA-1."
There are only three logical possibilities. 1) The reviewer is
exaggerating. 2) The reviewer has lost some of his auditory
acuity. 3) I have a bad HA-1 and need to return it quickly.
What I was hoping with this thread was to have a few HA-1
owners provide their first hand observations. I want to know
if my HA-1 is bad or normal. If normal, I can happily live with it.
Perhaps shielding and isolating class A amplifiers, in particular,
is difficult. I'm pretty certain that what I'm hearing is 60 Hz
EMI leaking into one or more stages of the amplifier section.
The question is really about how much leakage is within the
design and manufacturing tolerance.
Thanks
