Aleph 5 source resistor voltages

Keith Marrison · 6th July 2004, 09:01 PM

I recently completed an Aleph 5 using Kristians boards which was sounding great until there was a flash from inside the amp! this turned out to be due to my not isolating the power supply caps stud from the chassis(red face s all round). I ended up changing 3 of the IRFP240's but now have have source resistor voltages as follows:- 3 @ o.775V; 1 @ 0.958V & 2 @ 0.630V ! All other voltages are within a fraction of what they should be. And yes I did match the Mosfets to better than 0.1V. Any advice would be a
appreciated.Thanks in advance.
Keith

Nelson Pass · 7th July 2004, 04:17 AM

So they're a little off spec. I don't think they'll break otherwise.
Have you checked the Source resistors? Some of them might
have gotten burned a little and be off value - that would do it.

Since 3 of them seem to be averaging out at .7, I would bet
that the .958V one is the burned one.

Keith Marrison · 7th July 2004, 06:21 AM

WOW; my first post and a reply from the ONE AND ONLY!! My hands shaking. Thanks Nelson; it would appear tp be the source resistors; I have swapped IRFP240;s again and the main culprit's voltage dropped from above 1V to just below. Allsource resistors measure 1.1 ohm whemn measured cold and in circuit; can they be drifting when warm? I will swap them anyway.
May I say abig thank you to you; as I have enjoyed good sound from my system having built A40;s and for the past few years been the happy user of a Zen and Boz. Could not believe how loud 10 watts would go!! Once again many thanks.
Cheers; keith

Nelson Pass · 7th July 2004, 06:49 PM

Looks like it was the Mosfets after all.

6th July 2004, 09:01 PM	#1
Keith Marrison diyAudio Member Join Date: Jul 2004 Location: Gainsborough; lincolnshire	Aleph 5 source resistor voltages I recently completed an Aleph 5 using Kristians boards which was sounding great until there was a flash from inside the amp! this turned out to be due to my not isolating the power supply caps stud from the chassis(red face s all round). I ended up changing 3 of the IRFP240's but now have have source resistor voltages as follows:- 3 @ o.775V; 1 @ 0.958V & 2 @ 0.630V ! All other voltages are within a fraction of what they should be. And yes I did match the Mosfets to better than 0.1V. Any advice would be a appreciated.Thanks in advance. Keith

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Aleph-x hot source resistor	globalweb	Pass Labs	6	19th July 2007 02:26 PM
Aleph-type current source, but source follower this time	tschrama	Pass Labs	4	29th July 2005 12:55 PM
Aleph 2 source resistor comparison?	tomchaoda	Pass Labs	11	19th July 2004 06:20 PM
please HELP bourned Source resistor Aleph 30	wijgers	Pass Labs	3	12th April 2004 08:35 PM
Source output voltages and more	Sandy H.	Chip Amps	0	30th August 2003 04:21 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

7th July 2004, 04:17 AM	#2
Nelson Pass The one and only Join Date: Mar 2001	So they're a little off spec. I don't think they'll break otherwise. Have you checked the Source resistors? Some of them might have gotten burned a little and be off value - that would do it. Since 3 of them seem to be averaging out at .7, I would bet that the .958V one is the burned one.

7th July 2004, 06:21 AM	#3
Keith Marrison diyAudio Member Join Date: Jul 2004 Location: Gainsborough; lincolnshire	WOW; my first post and a reply from the ONE AND ONLY!! My hands shaking. Thanks Nelson; it would appear tp be the source resistors; I have swapped IRFP240;s again and the main culprit's voltage dropped from above 1V to just below. Allsource resistors measure 1.1 ohm whemn measured cold and in circuit; can they be drifting when warm? I will swap them anyway. May I say abig thank you to you; as I have enjoyed good sound from my system having built A40;s and for the past few years been the happy user of a Zen and Boz. Could not believe how loud 10 watts would go!! Once again many thanks. Cheers; keith

7th July 2004, 06:49 PM	#4
Nelson Pass The one and only Join Date: Mar 2001	Looks like it was the Mosfets after all.