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Old 22nd July 2012, 02:51 PM   #131
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Quote:
Originally Posted by Trevor White View Post
follow the current flow. If you use an opamp with class B or class AB output and the positive side is conducting then the current flows through the load back to the power supply common point.
Yes, and what is the load? I don't have a resistor to ground as the load. Most opamps (I'm talking about active XOs here) in the circuit are driving just the next opamp. The output opamp is a special case - it does drive current which returns to ground (assuming an unbalanced output, not my preference normally). Given my preference for inverting opamp configurations, the load current never touches the 0V, it always returns from one or other of the rails.

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If you had a fully differential configuration which did not reference ground then the cap across the +/- supply rail would make perfect sense but for a half bridge configuration with ground reference it doesn't make sense at all.
I do indeed prefer fully differential for a whole host of reasons, including this one.

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Maybe I am missing something but it sounds like a kludge that is trying to solve some other deficiency such as a poor board layout.
You are indeed missing something, but it is also a kind of kludge to solve poor board layout. Perfect board layout is quite impossible, there's always going to be a tradeoff. Optimising that tradeoff is what engineering is all about.
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Old 22nd July 2012, 03:02 PM   #132
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Quote:
Originally Posted by abraxalito View Post
Yes, and what is the load? I don't have a resistor to ground as the load. Most opamps (I'm talking about active XOs here) in the circuit are driving just the next opamp. The output opamp is a special case - it does drive current which returns to ground (assuming an unbalanced output, not my preference normally). Given my preference for inverting opamp configurations, the load current never touches the 0V, it always returns from one or other of the rails.



I do indeed prefer fully differential for a whole host of reasons, including this one.



You are indeed missing something, but it is also a kind of kludge to solve poor board layout. Perfect board layout is quite impossible, there's always going to be a tradeoff. Optimising that tradeoff is what engineering is all about.
If it's a non-inverting opamp amplifier circuit then it is referencing ground. A Sallen and Key or Infinite gain active filter will have some elements connected to ground. A two resistor inverting circuit will have it's non-inverting input either connected directly to ground or be referenced to ground through a low impedance path such as a capacitor that has one side connected to ground.

You can't avoid the ground point that's why the decoupling between the two power rails doesn't quite make sense.
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Old 22nd July 2012, 03:08 PM   #133
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Quote:
Originally Posted by Trevor White View Post
If it's a non-inverting opamp amplifier circuit then it is referencing ground.
Indeed, but in my last post I said this:

Given my preference for inverting opamp configurations

Quote:
A Sallen and Key or Infinite gain active filter will have some elements connected to ground.
I prefer to use MFB, it has the +ve opamp input as the connection to ground - this is a signal ground, not a power ground. Decoupling is for power.

Quote:
A two resistor inverting circuit will either be connected directly to ground or be referenced to ground through a low impedance path such as a capacitor that is connected to ground.
I can't see how. A two resistor inverting config just has +ve input to 0V. No capacitor is needed, though if a bias current compensation resistor is used then a cap might be placed in parallel with it. Only sub microamp currents are going to flow here.

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You can't avoid the ground point that's why the decoupling between the two power rails doesn't quite make sense.
I'm not avoiding the ground point, rather I'm avoiding putting current into it. Significant difference.
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Old 22nd July 2012, 03:11 PM   #134
chaparK is offline chaparK  Luxembourg
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I sincerely apologize but would like to ask you guys to kindly discuss extensively decoupling in a separate thread.
This one is about DSP, and decoupling is not a central topic here. Hope you don't mind, and sorry again.
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Old 22nd July 2012, 03:13 PM   #135
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I don't mind at all, and no apology required - but are you going to decouple your CS3318?
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Old 22nd July 2012, 03:15 PM   #136
chaparK is offline chaparK  Luxembourg
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Originally Posted by abraxalito View Post
I don't mind at all, and no apology required - but are you going to decouple your CS3318?
Chances are I have
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Old 22nd July 2012, 03:23 PM   #137
ds23man is offline ds23man  Netherlands
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And what did you do with the mute input ( pin 4)?
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Old 22nd July 2012, 03:36 PM   #138
chaparK is offline chaparK  Luxembourg
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Originally Posted by ds23man View Post
And what did you do with the mute input ( pin 4)?
Hi ds23man,

Thanks for your advises.

The mute pin is connected to the logic and can be set low or high on demand, no need to worry!

Cheers
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Old 22nd July 2012, 04:02 PM   #139
ds23man is offline ds23man  Netherlands
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Pin 4 usage is a nice omission in the datasheet, you can be tempted not to use it if you do all the muting with Mute all register. It is presented as a hardware mute..... Fact is it has to be terminated, it must be high or low all the time. If you use a switch to control this pin you have to use a pull up or down configuration. If you don't **** happens.........
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Old 22nd July 2012, 04:18 PM   #140
yoke is offline yoke  Croatia
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Hi all...
I would be interested but have some questions, just to see if I get this right ...
sorry for bad english...

Now i have active 3 way loudspeakers and useing behringer dcx2496 as crossover

So with this project I could replace it and have better sound ?

I could use it as ;

Source > DSP Xover (which have onboard,6chanell, DAC and volume control) > amplifiers > drivers

I would not nead preamp ?
Amps are Pass Aleph series clones.

Thanks

Last edited by yoke; 22nd July 2012 at 04:24 PM.
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