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RE: Hello Alan

Posted by Bill Way (A) on December 24, 2015 at 08:45:14

In Reply to: Hello Alan posted by Cousin Billy on December 23, 2015 at 23:13:45:

Sorry, Billy, hope lunch was good.

The red and white sides of a channel are not the positive and negative portions of the waveform. They are the positive and negative portions of the current flow.

Any circuit has to provide a closed path for current to flow. Look at the one channel diagram: if the cartridge is our signal generator (the circle with the sine wave inside), and it has colored leads, in this case red and blue, it connects to the phono stage (here shown as a resistor) from both its red and blue sides. Yes, I know the load a phono stages presents to a cartridge is more complicated than a simple resistor, but let's leave that aside for now.

If it is generating a sine wave, during one half of the cycle current will flow clockwise around the diagram, and during the other half of the cycle current will flow counter-clockwise. But at all times that current is flowing, it flows through both the red and blue wires. There are no dead ends. Also, while current in one direction will push the woofer out, and current in the other direction will suck it in, current must flow through both the red and blue wires whenever current flows at all, and regardless of the direction of current flow.

For single-ended gear, the red and blue connect to the pin and shield of the RCA plug. Whenever current is flowing, both the pin and shield carry the signal, i.e. the current.

The same diagram can be used to show the phono stage (signal generator) and amplifier (resistor). Again, current flows through both the pin and shield of the RCAs. If using balanced gear, it flows through XLR pins 2 and 3 instead of the RCA pin and shield. It's like putting you, your turntable, and your electronics inside a big metal box that shields you from all the nastiness that can intrude from the outside world.

Because single-ended gear sends the signal through the shield, it is more susceptible to picking up various interference from the outside world, particularly when dealing with the tiny currents involved in phono cartridge outputs. But there are ways to design ICs from tonearm to phono stage that minimize this, such as a second outer shield. In my system, that second shield is connected at one end to the tonearm housing and turntable metal, and at the other end is connected to the preamp chassis ground.

For single-ended ICs, I connect the outer shield to the RCA shield at one end only, which lets the outer shield actually do some shielding from RF et al. The isolation it provides is not as robust as balanced gear, but I haven't yet had a home situation that could not be made completely quiet. (Hint: with the outer-shield-at-one-end configuration, where you place the shield "drains" can make a difference. In my case, they are all on the preamp end of the ICs.)

Cheers,
WW
"Put on your high heeled sneakers. Baby, we''re goin'' out tonight.

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