Cleaner Power, Lower Noise

I switched my line level components over to the dedicated amplifier circuit.  As a result, wideband amplifier noise dropped from 1.8mV to 1.7mV, and there was a similar small drop in A weighted noise.

More impressive was comparing the AC lines directly with my AudioPrism Noise Sniffer.  I can now give these reading quantitative values by holding an SPL meter directly above the widest part of the sniffer speaker.  For SPL meter, I used a very accurate mobile device SPL app.  The dedicated line got a measurement of 78dB.  The old household line got a measurement of 100dB (!) as it was buzzing like hell. I got that measurement after turning off the dimmer for the kitchen fluorescent lamp.  Strangely, with the dimmer on at 50% brightness level, the line noise level was lower.  The old household circuit is crazy, it goes from the the outside light in front of the garage to the outside light in back of the house which are both fluorescent with photosensors.  In between it goes to the entry light and outlet and the kitchen light/fan which is on a special fan-compatible dimmer.

It's hard to tell exactly how much the sound improved since I've been making so many changes that have improved signal-to-noise ratio over the past month or so.  The overall result is that the sound is very warm and imaging is very stable.

I think I'll keep the line level components connected to this circuit in the future.  In the past, I had used this line exclusively for the Krell FPB 300 amplifier, which draws current mightily sometimes.  But I think now it's worth keeping the line level components on this line also, and if the Krell lowers the line voltage significantly the new UPS will restore it, but I don't expect that to happen often.  If it turns out this line causes the UPS to make too much noise when the Krell is on it, then I'll have to move back to the old circuit.

The dedicated amplifier circuit has these specifications: 120V, 20A Breaker, 10ga wire, wired straight to main power entry box, insulated ground, oyade outlet.  Cost the better part of $1300 to install.

The reduction in noise could come from less noise on the hot, neutral, and ground wires.  But it could also come from putting both line level components and amplifier on the same AC circuit.  For the purposes of deciding how to do my connections, this answer to this question is unimportant.  But for audio science, the question is important, because reducing amplifier noise by using a quieter AC might be considered tweaky and not part of standard audio engineering.

To have a controlled experiment, I would have to try one or more additional comparisons.  For example, having all components, including the main amplifier (currently a Parasound HCA-1500A because the Krell is waiting for repair) on the noisy line.  Then I could compare the two cases:

1.  All components on noisy line
2.  All components on quiet line

which would single out the issue of noisy or quiet line, and remove the additional issue of having components on one or two lines.

Actually, because I had been operating on two lines before, I had previously ground-lifted the Parasound.  For some reason, every Parasound amplifier I've had has needed to be ground-lifted or connected to an otherwise ground-lifted system.  Perhaps now, with everything on the same line, I could operate the amplifier without being ground lifted, but I made the change internally.

But since I already ground lifted the amplifier, the issue regarding the previous operation of components across two different AC lines should have been relatively small.

I am interested in the scientific question, so I expect to go back and do some additional experiments, but I think that operating both line level components and amplifier from the dedicated circuit makes the best sense.

When doing the noise sniffing, I also tested the outlets of the Belkin PureAV AVU1500 when plugged into the quiet circuit.  In that condition, they measured the exact same "noise sniffer level" as the circuit itself, 78dB.  My interpretation is that 78dB is already as quiet as AC gets.  The other interpretation might be that the PureAV filtering doesn't do anything.  But I recall (no numbers) that when the PureAV was plugged into the noisy circuit, it was still quiet.  So that supports the idea that the Belkin filters power pretty well, but when you are already starting from fairly clean power, it may not do much.  And clean power may mean simply a dedicated circuit with insulated ground.