One thing that still puzzles me about Single-ended amps is the DC offset.
So a push-pull is an AC amplifier and the output varies up and down from ground right?
A Single ended voltage output is offset above ground?
Would than mean that the speaker cone on an AC/PushPull amp oscillates about the ‘home’ position back and forward but that a single-ended driven speaker only moves forward from the ‘home’ position?
If so, no wonder they sound different. The whole wave is moving a pressure wave forward on a Single-ended amped speaker and only the positive half of the cycle on a pushpull.
Having a hard time grasping this stuff. Thnx.
Greg
So a push-pull is an AC amplifier and the output varies up and down from ground right?
A Single ended voltage output is offset above ground?
Would than mean that the speaker cone on an AC/PushPull amp oscillates about the ‘home’ position back and forward but that a single-ended driven speaker only moves forward from the ‘home’ position?
If so, no wonder they sound different. The whole wave is moving a pressure wave forward on a Single-ended amped speaker and only the positive half of the cycle on a pushpull.
Having a hard time grasping this stuff. Thnx.
Greg
You can't put DC into a speaker so the amp must have 0VDC at its output,
either by using +/- power supplies, or else a coupling capacitor or transformer.
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A single polarity supply has +ve supply rail and -ve supply rail.
One or other will be used as the zero volt reference. (usually we see the -ve supply taken to the zero volt reference, but it does not have to be so)
Using -ve as the zero volt reference the supply becomes +Vdc and 0Vdc
The output to the load/speaker is usually around half the supply voltage i.e. ~50%Vdc
This will destroy speakers and headphones and other low DC resistance loads.
The usual way to protect your DC sensitive load is to insert a DC blocking capacitor in the feed to the load.
You will find many DC blocking capacitors in amplifiers. Each must be rated to higher than the worst case peak voltage that could occur across the capacitor.
For an output capacitor this would be > +Vdc as the capacitor rating.
One or other will be used as the zero volt reference. (usually we see the -ve supply taken to the zero volt reference, but it does not have to be so)
Using -ve as the zero volt reference the supply becomes +Vdc and 0Vdc
The output to the load/speaker is usually around half the supply voltage i.e. ~50%Vdc
This will destroy speakers and headphones and other low DC resistance loads.
The usual way to protect your DC sensitive load is to insert a DC blocking capacitor in the feed to the load.
You will find many DC blocking capacitors in amplifiers. Each must be rated to higher than the worst case peak voltage that could occur across the capacitor.
For an output capacitor this would be > +Vdc as the capacitor rating.
So I have read a bunch of Mr. Pass's articles and still am of the understanding that the waveform from a Single-ended amp is an alternating signal offset above zero volts. So essentially a varying DC voltage. A capacitor cannot turn DC to AC.
All I can see in these articles about single ended power supplies is that it does not use a +/- power supply. It uses a +v/GND supply. So there is no way the bottom end of the signal can be a negative voltage. And this means the speaker cone only drives forward from the 'home' position and not back and forth as with a push-pull.
Can someone show a voltage output waveform from a single -ended amp please? Thnx.
Greg
All I can see in these articles about single ended power supplies is that it does not use a +/- power supply. It uses a +v/GND supply. So there is no way the bottom end of the signal can be a negative voltage. And this means the speaker cone only drives forward from the 'home' position and not back and forth as with a push-pull.
Can someone show a voltage output waveform from a single -ended amp please? Thnx.
Greg
The steady DC output voltage (before any blocking element) can be either 0VDC
or some value like +15VDC. The output signal waveform in a single supply circuit is the
same as that in a +/- supply circuit, except it is riding on a DC voltage that is nonzero.
All single supply amplifiers have a DC blocking output circuit, such as a capacitor
or transformer. Speakers normally cannot accept DC unless they have a DC blocking
circuit (such as a series capacitor like some KEFs and Quads had at one time).
Here is an example of a single supply amplifier, note the output capacitor to block the DC
present at the output. Also note the DC blocking input capacitor to protect the source.
http://www.seekic.com/uploadfile/ic-circuit/20113162913596.gif
I suggest you read up on single supply amplifiers. https://www.ti.com/lit/an/sloa030a/sloa030a.pdf
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A varying DC voltage is by definition an AC voltage when you remove the DC offset which is easily done with the aforementioned blocking capacitor as is found in single supply solid state amplifiers, PP or otherwise. A transformer can also be used as is often the case in SE tube amplifiers.
The resulting waveform in an ideal world would look exactly the same as one from a PP amplifier operating on dual rails.
It depends only from power supply, not from PP or SE. If amplifier has single rail supply (GND V+), it need to be DC decoupled from speaker. If amplifier has dual power supply rails (-V GND +V), no decoupling needed. For example, JLH amplifier - PP and has single rail supply and DC decoupling capacitor. Single rail amplifier do not need decoupling on one case - if it 'bridge' amplifier.
And this is SE dual rail amplifier which do not has DC offset:
Schematics from Pass articles.
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