Square wave testing....Cap value

ashok · 7th August 2005, 05:08 PM

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 ?
Cheers.

AndrewT · 7th August 2005, 05:32 PM

Hi,
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.
Cheers.

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!

Cheers,
Greg

7th August 2005, 05:08 PM	#1
ashok diyAudio Member Join Date: Jun 2002 Location: 3RS	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 ? Cheers. __________________ AM

7th August 2005, 05:32 PM	#2
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, 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. __________________ regards Andrew T.

8th August 2005, 03:37 AM	#3
ashok diyAudio Member Join Date: Jun 2002 Location: 3RS	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. Cheers. __________________ AM

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8th August 2005, 08:00 AM	#4
amplifierguru Account Disabled Join Date: Aug 2004 Location: Earth	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! Cheers, Greg

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