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In Reply to: RE: Lew, I'll try to explain posted by ahendler on December 23, 2015 at 17:46:10
You are probably correct.
I am not an electrical engineer. I know very little on the subject.
This is how I look at it;
A phono cartridge has two leads per channel. The red lead is the positive portion of the waveform, analogous to the speaker driver moving outwards. The white lead is the negative portion of the waveform, analogous to the speaker driver moving inwards.
A truly balanced signal preserves both sides of the waveform through the entire amplification process.
A single ended amplification chain uses the positive portion (red lead) of the waveform, but what happens to the negative portion of the waveform?. I believe half of the music is relegated to ground?
Or am I completely out to lunch?
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.)
"A man need merely light the filaments of his receiving set and the world's greatest artists will perform for him." Alfred N. Goldsmith, RCA, 1922
I admit this can be a difficult concept to grasp, but please re-read what I wrote. It is not the case that "half the wave form" is lost in SE connections. This is not to say that I completely agree with Alan that there is nothing to be gained in home audio systems by using balanced connections. Perhaps Ralph can chime in with a more erudite discussion that will edify you.
Anyway, in your re-statement of a specific question regarding an MA1, it is possible to give a better answer than I did the first time. In Atma-sphere amplifiers that provide an RCA jack input as well as an XLR input, the user performs an act that connects the grid of one side of the dual-differential cascode input topology to ground,when he or she elects to use the RCA jack. The other grid of the input stage is driven by the input coming via the RCA jack. (I cannot recall whether connecting the unused grid to ground is done with an external switch or with a modified XLR plug, because it's been so long since I've even thought about driving the amp with an SE input.) However, the amplified signal still appears at the plates on both sides of the dual-differential cascode, which via cathode-followers drives the output stage still in balanced mode. So, I think it's correct to say that in an MA1, SE input is converted to balanced output. But it's the balanced output of what was originally an SE signal, so there was no noise cancellation (Common Mode Rejection) operating on the signal that reached the RCA jack. Some of that will be cancelled in the balanced circuit, I think.
Note. This response is very specific to Atma amplifiers. I daresay most other commercial amplifiers that offer both XLR and RCA inputs will handle the signal differently. That is to say that many products are "feaux balanced". For this reason also it is misleading to think that you can look for XLR input jacks and assume that the product contains a balanced circuit design inside.
I admit this can be a difficult concept to grasp, but please re-read what I wrote. It is not the case that "half the wave form" is lost in SE connections. This is not to say that I completely agree with Alan that there is nothing to be gained in home audio systems by using balanced connections. Perhaps Ralph can chime in with a more erudite discussion that will edify you
Its best if you think of an non-inverted signal and an inverted signal, rather than 'half the waveform' which only introduces confusion. IOW, both phases are being dealt with at the same time.
When you drive the MA-1 through the RCA input, the input is single-ended even if the source is balanced. Single-ended and balanced are inherently incompatible so you usually have to jump through some hoops to make the components work together- special adaptors, transformers and the like. But the thing you want to remember is that the signal is either balanced, or it isn't, no in-betweens.
Suffice it to say, Atma-Sphere for life.
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