leach troubleshooting

audiofan · 25th October 2009, 11:10 PM

I have a leach amp working well, very low output offfset ( below 3 mV ) but at turn-on a massive DC bump that push speaker full travel.

Where should I look first ? capacitor in feedback loop ? power supply simetry at turn on ?

Iain McNeill · 25th October 2009, 11:21 PM

Most amps will do this due to the high loop gain and the big initial input error on power up. Most of us use a delay relay which connects the outputs after the amp has stabilized. Usually part of a protection circuit..

You could do same with changeover switch, or just plug speakers in after turning amp on.

BobEllis · 25th October 2009, 11:28 PM

According to professor Leach, you could get a bump if the main filter caps are not fully discharged when you turn the amp back on. Do you have bleeder resistors across the main filter caps?

Edit: My Leach amps use cheap PSU caps and I don't get a bump even without bleeder resistors or a delay.

audiofan · 26th October 2009, 01:19 AM

Quote:

Originally Posted by BobEllis

According to professor Leach, you could get a bump if the main filter caps are not fully discharged when you turn the amp back on. Do you have bleeder resistors across the main filter caps?

Edit: My Leach amps use cheap PSU caps and I don't get a bump even without bleeder resistors or a delay.

I made the test twice and you had the exact answer, capacitor must fully discharge before turnig on. merci beaucoup

25th October 2009, 11:10 PM	#1
audiofan diyAudio Member Join Date: May 2003 Location: quebec	leach troubleshooting I have a leach amp working well, very low output offfset ( below 3 mV ) but at turn-on a massive DC bump that push speaker full travel. Where should I look first ? capacitor in feedback loop ? power supply simetry at turn on ?

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25th October 2009, 11:21 PM	#2
Iain McNeill diyAudio Moderator Join Date: Oct 2007 Location: Santa Cruz, California	Most amps will do this due to the high loop gain and the big initial input error on power up. Most of us use a delay relay which connects the outputs after the amp has stabilized. Usually part of a protection circuit.. You could do same with changeover switch, or just plug speakers in after turning amp on.

25th October 2009, 11:28 PM	#3
BobEllis diyAudio Member Join Date: Sep 2003 Location: Upstate NY	According to professor Leach, you could get a bump if the main filter caps are not fully discharged when you turn the amp back on. Do you have bleeder resistors across the main filter caps? Edit: My Leach amps use cheap PSU caps and I don't get a bump even without bleeder resistors or a delay.

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