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Old 13th May 2009, 05:11 PM   #111
jwb is offline jwb  United States
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Quote:
Originally posted by thanh1973

My feeling (I have no experience on this) then is that output impedance at 0Hz (pure DC) is more important than at high frequency (or any frequency for that matter).

If my thinking is completely wrong please help me understand (remember my question refers to highly biased class A circuits).
You're not completely off-base here, but the problem is that no such circuit exists in reality. You are absolutely correct that a circuit with more constant current draw can tolerate a less capable regulator. Conversely a circuit where the current consumption slews all over the place needs a great regulator.

In reality it's good to focus on both. Try to make circuits with constant current draw, or balanced circuits where the current flows in local loops, or try to make the quiescent current much greater than the dynamic current. Then determine the dynamic current and the output impedance you can tolerate and design a regulator having that output impedance.

You're wrong about zero Hz, however. It's desirable to have a flat output impedance in the passband, because otherwise you will skew your circuit's frequency response.
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Old 13th May 2009, 05:15 PM   #112
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Hi jwb,

Actually, it was the "look" of your preamp design that prompted the choice of colour / section and I was very suprised at how much simpler it made it to follow the cct - will be quite useful later on for different variations - thanks for the idea, too.
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Old 13th May 2009, 05:54 PM   #113
iko is offline iko  Canada
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Good start guys!!! A few comments, some of which you can safely ignore.

* my first concern would be the pins on the irfp9240. In my datasheet it shows as G D S, 1 2 3
* the mosfet gate resistors, as close as possible to the gate, even if it looks ugly
* the signal path, in -> out, should be as straight as possible; this helps with higher frequency response
* C2 can be safely smaller
* should C3 be closer to the output?

This is it for now.

Edit: I can show this ugly duckling that I'm currently working on. I am not suggesting you should do it this way, but it seems appropriate to compare notes.

Click the image to open in full size.

As always, comments appreciated greatly.
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Old 13th May 2009, 06:06 PM   #114
Salas is offline Salas  Greece
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How do you heatsink m1 without obstruction especially in heavier settings?
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Old 13th May 2009, 06:08 PM   #115
Salas is offline Salas  Greece
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Quote:
Originally posted by ikoflexer

* my first concern would be the pins on the irfp9240. In my datasheet it shows as G D S, 1 2 3
* the mosfet gate resistors, as close as possible to the gate, even if it looks ugly
Yes, James must correct along with the BCs.
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Old 13th May 2009, 06:10 PM   #116
iko is offline iko  Canada
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Quote:
Originally posted by Salas
How do you heatsink m1 without obstruction especially in heavier settings?
Yes, good catch! It would, and I'm still trying to push things around to come up with a better solution. This is very preliminary, just started on it, playing with ideas.

This is a pcb for the experimental V2, you probably noticed already. I've stumbled upon a small change which further improves performance. Very small steps, but at this level, I'm happy even with incremental improvements. We'll see if in real life it proves to be good.
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Old 13th May 2009, 06:18 PM   #117
Salas is offline Salas  Greece
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OK. Lets focus into constructable shunts. We must keep it focused. Two shunts. 1 standard with PCB. 2. A possible V2, a bit more complex, along its own PCB if it really works as a better sounding prototype on its PCB.
Shunts for the people!
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Old 13th May 2009, 06:28 PM   #118
iko is offline iko  Canada
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salas, I don't want to impose v2. I you think we should stay focused on v1 for now I can refrain from the v2 topic.
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Old 13th May 2009, 06:34 PM   #119
Salas is offline Salas  Greece
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To the contrary! The standard version will be out soon on excellent (and debugged) PCB from James. 10s of people are extremely happy with it by now in many voltage and current settings. That is a done and out shunt.

Running a possible V2 plan is healthy. We will recommend it additionally only when you will say that it actually sounds better to SR1 on a final PCB of yours without oscillations. That's all. Brazillian soccer. Fast, short passes to the goal.
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Old 13th May 2009, 10:10 PM   #120
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Sorry Ikoflexer
You obviously didn't measure the output impedance of the last circuit I posted.
Or if you did then maybe I have stuffed up my own measurement.
Could you tell me what you get just to be sure I am doing it right?
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