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Old 11th February 2006, 10:11 AM   #1
AndrewT is online now AndrewT  Scotland
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Question NE5534 compensation ?

Hi,
for unity gain the 5534 needs about 22pF as Ccomp.

for gains greater than 5, Ccomp=opencircuit.

Is there a way to determine the value of Ccomp for gains between 1 and 5?

Is there any advantage in reducing Ccomp to the lowest value that consistently achieves stability?
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Old 11th February 2006, 10:38 AM   #2
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Intermediate gains require an intermediate value, I would try 10 or 12pF for x2 and 4p7 or 6p8 for x3

If you overcompensate with 22pF for x2 or x3 you waste bandwidth
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Old 11th February 2006, 12:48 PM   #3
AndrewT is online now AndrewT  Scotland
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Hi all,
David seems to be indicaing that there is an advantage in keeping the Ccomp low.

His suggested values also fit a model:- Ccomp~=22pF/gain.

Any other comments?
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Old 11th February 2006, 01:00 PM   #4
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I do not think there is some formula for best Ccomp value.
Because different circuits, different loads and each individual NE5534 can have slight variations.

To set the lowest possible capacitance can only be done by using oscilloscope.

As you can see NE5534 is already compensated internally.
With 12 pF capacitor, that will be in parallel with external.
Across pins 5 and 8.

NE5534 does not need any external comp for gain >= 5
NE5534 will be stable at unity gain = 1, with 22 pF

Gain, Int, Ext cap
x5 = 12pF
x3 = 12pF + ??
x1 = 12pF + 22pF
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Old 11th February 2006, 01:36 PM   #5
AndrewT is online now AndrewT  Scotland
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Hi,
I am begining to understand the workings of 5534 as well as opamps generally.

My current power amp uses 5534 gain of x2 with Ccomp=22pF as a pre conditioning stage (cap coupled at in & out) before the main 3stage amp.

I am pondering further modifications.
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Old 11th February 2006, 02:07 PM   #6
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If you use 22 pF you won't have to think. It just works. If you want to tune the value put in square wave and observe when you'll get a good output signal.
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Old 11th February 2006, 02:09 PM   #7
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Default Re: NE5534 compensation ?

Quote:
Originally posted by AndrewT
Is there any advantage in reducing Ccomp to the lowest value that consistently achieves stability?
For this particulary opamp, no not really.
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Old 11th February 2006, 02:14 PM   #8
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Is this part of an overall feedback loop?
If it is then disturbing the opamp bandwidth will have consequences.
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Old 11th February 2006, 02:15 PM   #9
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Default Re: NE5534 compensation ?

Quote:
Originally posted by AndrewT


Is there any advantage in reducing Ccomp to the lowest value that consistently achieves stability?
Yes...you will have more bandwidth and more feedback in the high frequencies , with the consequent reduction in distortion...

The NE5534 is a great Op-Amp...
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Old 11th February 2006, 02:37 PM   #10
AndrewT is online now AndrewT  Scotland
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Hi all,
thanks so far.
the times 2 gain at the front end is inside it's own feed back loop and completely separate from the global loop around the 3stage amp that follows. There is DC block & RF filter between the two gain stages as well as DC block at the input.

I am almost set up to post the schematic but the 1.7Mb pic does not fit my floppy from work to home where I can compress it for posting. Maybe it would be easier to draw in schematic software
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