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ashok 7th August 2005 05:08 PM

Square wave testing....Cap value
Most load tests with square waves seem to be 8 ohms parallel with 2 uF. I found that 8 ohm parallel 0.1uF created more problems than 2uF. Additionally 8 ohms parallel 0.01uF sometimes causes oscillation on the horizontal flat portions. Sometimes very hard to get rid of.

I also saw someone on the web say that he also found 0.1uF more problematic than 2 uF. I can't remember where that was.
What's the experience on this forum ?

AndrewT 7th August 2005 05:32 PM

I have seen it recommended to test with a range of capacitors.
I think from 100nF to 2uF so you have seen the extremes, now check in between to ensure stability throughout the whole operating condition range.

ashok 8th August 2005 03:37 AM

I use 0.01uF, 0.1uf , 0.22uF , 0.47uf, 1uF, 2.2uF, 4.7uF. All film caps 250 volt rating. The 0.01 and 0.1 are 630 volt films.
Covers the whole range I guess. The 4.7uF might be a bit extreme.

amplifierguru 8th August 2005 08:00 AM

Intrinsically high output impedance amplifiers will be particularly sensitive to C loading so, in general, you need to test for low and high C. Of course an input HF filter will reduce the perturbation as the higher frequency harmonics do not get through to the amplifier proper to stimulate vagaries!


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