stability

djdamix · 6th January 2005, 10:23 AM

I'm developping an amp which sounds ok, but I am wandering
1)how I can test its stability ?
2)Why do people use zobel network on the output (I mean L & C )
3)How does it increases stability ?

David

Mr Evil · 6th January 2005, 01:56 PM

1) Depends on how unstable the amp is. If it's very unstable then it will be obvious, with the output oscillating at a particular frequency, usually causing heating of the output devices. If it's marginally stable then you may see bursts of oscillation. An oscilloscope is indispensable here.

A good test is to put a square wave into the amp and look for ringing at the output. If there is no ringing then the amp should be perfectly stable. A lot of ringing and you have a problem. You may want to test for stability with a capacitive load too.

2) For stability of course. BTW, you mean R + C at the output. If there's an L then it's not part of the Zobel network, although still there for stability.

3) It provides a low impedance path to ground at high frequencies. This helps compensate for the rising output impedance of the amp at high frequencies and/or inductive loads.

anatech · 7th January 2005, 01:25 AM

Don't forget to run it untill it's quite warm and redo your tests. Things can change with temperature.
-Chris

djdamix · 7th January 2005, 07:30 AM

good idea! I'll try

Thanks

6th January 2005, 10:23 AM	#1
djdamix diyAudio Member Join Date: Jun 2004 Location: Lyon	stability I'm developping an amp which sounds ok, but I am wandering 1)how I can test its stability ? 2)Why do people use zobel network on the output (I mean L & C ) 3)How does it increases stability ? David

6th January 2005, 01:56 PM	#2
Mr Evil diyAudio Member Join Date: Aug 2004 Location: Behind you	1) Depends on how unstable the amp is. If it's very unstable then it will be obvious, with the output oscillating at a particular frequency, usually causing heating of the output devices. If it's marginally stable then you may see bursts of oscillation. An oscilloscope is indispensable here. A good test is to put a square wave into the amp and look for ringing at the output. If there is no ringing then the amp should be perfectly stable. A lot of ringing and you have a problem. You may want to test for stability with a capacitive load too. 2) For stability of course. BTW, you mean R + C at the output. If there's an L then it's not part of the Zobel network, although still there for stability. 3) It provides a low impedance path to ground at high frequencies. This helps compensate for the rising output impedance of the amp at high frequencies and/or inductive loads. __________________ https://mrevil.asvachin.eu/

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7th January 2005, 01:25 AM	#3
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Don't forget to run it untill it's quite warm and redo your tests. Things can change with temperature. -Chris

7th January 2005, 07:30 AM	#4
djdamix diyAudio Member Join Date: Jun 2004 Location: Lyon	good idea! I'll try Thanks

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