I have worked on high end Crown amplifiers and others along that line. These
are used in professional studio environments. They use a complete set of
power supplies for each channel of audio. Some models only share the same
power transformer, but the rest of the power supply is separate.

If you want to have some very good quality sound, that you cannot experience
with any of the home audio gear, get in to collecting and building up a
sound system using professional audio equipment. There is a big difference!

--

JANA
_____


"Arfa Daily" wrote in message
...

"punkinaro" wrote in message
oups.com...

Arfa Daily wrote:

======

As far as I recall, the power supply on these is common to all channels,
thus if the hum is on one channel only, it is highly unlikely that it is
being caused by the main smoothing caps. The first thing to establish is
if
the hum is affected by the setting of the volume control. If it is, then
the
problem will likely be a front-end grounding issue.

thanks for the answers, but what is a front end grounding issue?
Excuse my ignorance, I am starting to pick up these old receivers for
few dollars, and I am amazed by the sound quality ( I also have a
small, old Sansui R-606 that sounds incredible), and I want to learn
the basics.
I think I have a new hobby.


OK. 'Front end' is engineer speak for the input select / preamp / tone
control etc stages of an amplifier, and is generally accepted as being any
and all of the circuitry from the input sockets, as far as the volume
control. After the volume control is usually taken to be 'output stage' or
'power amp', and the actual circuitry will include predriver, driver, and
output stages.

If you connect a signal to an amplifier, with the ground disconnected,
there's a good chance that the amp will produce a loud hum, which can be
controlled by the volume setting. This tells you that the problem is 'front
end' related. The results of bad ground connections internal to an amplifier
can vary depending on the exact design and layout, but if, for instance, the
ground pin of an input socket went dry jointed in the board, or sheared
off - both common failures - you may well still get correct audio through
the channel, due to the ground connection being intact on the other channel,
but you may also get a degree of hum on the 'bad' channel, due to the ground
following an abnormal path via the other channel.

If you have a hum which is not affected by the volume control, then this
indicates that the problem is post the volume control, OR is power supply
related. As noted by myself and electricitym, a power supply related problem
will, in most cases, affect both channels, as a common power supply is
typically used to supply both channels. The exception to this occurs in a
few high-end amps, which employ separate power supplies for each amplifier.
You can think of these amps really, as being two independant mono amps built
on the same chassis, but with ganged controls. Your Yamaha employs a single
common power supply, which is why I said that if you have hum on one channel
only, the problem is *unlikely* to be power supply related. Hope this helps
you to understand it a bit better. It's easy for those of us who work on the
stuff all day, to forget that many people asking questions on here are
either amateur, or just starting out.

Arfa