Zero Crossing with Single Supply?

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promixe

promixe

Well-known member
Joined
Jun 9, 2008
Messages
193
Location
Midwest, US
Pardon my absence of AC theory, but:

WHERE is ZERO axis when detecting zero crossing on a single +24V rail signal? Is it precisely +12V (Vcc/2)? Is this the reference I have to feed the detector?

Thanks in advance for your answers! +)
 
So, in the case below, pin F is the unbalanced output, then pin B is the reference?...

ba283am.jpg
 
Thanks for the quick answer! But just so I understand the principle behind this: pin J is the ground. What I'm trying to visualize is - once a positive piece of a sine wave crosses the ground ("J") it goes WHERE? Since this is a single supply it can't go _below_ ground, i.e. into negative voltage... Or am I not looking at this the right way?

ba283am2.jpg

 
Thanks to C7, there is no DC at F. So with no signal, The probe will read 0 volts at this point. Then, with postive voltage swing, it will read positive, but respectively, when the voltage will swing the other way, it will read negative, because F is only "DC referenced" to J (0 volts), via R8.
...I don't know if I'm clear, an not sure I perfectly right either, but that's how I see it.

Laurent.
 
In the case of the Neve, being class A, all the action electronically happens between 0 & 24v it doesn't go negative.  Circuits only operate between the constraints of the power supply rails in this case 0-24v. 
 
..exactly. And the DC-blocking output capacitor offsets this to be symmetric around the ground reference, by removing the zero-Hz component...

Jakob E.
 
interesting thread.
so a 0v signal will idle at +12v?

sorry to hijack, that was my assumption of why a class a guitar amp would be so inefficient.
is that the same thing?
 
so is what you are saying, umm...
neve single sided 24v circuit is the same basic
"voltage headroom" operating area as a + & - 12volt
circuit?
 

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