aleph 5 oscillating???

george a · 2nd February 2005, 02:39 PM

Hi all

After much stuffing around i have seperated A5 power supply for the pcb's and output mosfets after upgrading heasinks to much larger size.

However i now have other problems which I didn't have before!!

1. I now have approx 1V offset at speak terminals as opposed to approx 50mV previously.

2. I now have hum at ouput (even with now input wiring to pcb.)

3. Votages on pcb appear ok.

4 . voltage across 1 source resistor on one mosfet starts off ok then rises rapidly and the other mosfets current essontially drops to zero....ish.

Is this one mosfet oscillating.????

I replaced it with another (matched ) and again voltage started off ok and then started to rise, is the mosfet dud , (it has 33ohm across gate to source...

the ouptut mosfet are only a couple of inches from the pcbboard.

any suggestions.????

thanks in advance

cheers

kropf · 2nd February 2005, 02:53 PM

The negative rail of the front end has to be the same as the negative rail on the output stage.

Jeremy

george a · 2nd February 2005, 03:01 PM

Hi Jeremy
They are the same as they are fed from same point
I am using Mark Finnis PCb + mosfet pcb's

BTW I removed 1 ohm source resistor and turned on to check other mosfet and the resistor R22 221ohm which goes from Q2 (Ztx450) to junction between source of mosfet and 1ohm resistor ended up smoking itself

george a · 2nd February 2005, 07:29 PM

Anybody ...please??

george a · 2nd February 2005, 11:53 PM

please..??

BTW I don't have an oscilloscope to have a look at what's happening

george a · 3rd February 2005, 06:08 AM

anybody....please??

peranders · 3rd February 2005, 07:52 AM

The experts sleep sometimes

george a · 3rd February 2005, 08:46 AM

Yes Peranders , the experts do sleep sometimes.

the problem is idiots like ME stay up all night worrying about what we've done wrong.

Sweet dreams , good night - sleep tight

regards from down under

macka · 3rd February 2005, 11:13 AM

Sounds like a wiring fault,

Post a few pictures so we can understand

Macka

george a · 3rd February 2005, 12:48 PM

sort of a wiring fault macka

looks like a dodgy 1 ohm resistor in the location that's blown 2 mosfets so far.
I replaced the mosfet with a sacrificial non matching one and put in a 1.5 ohm resistor just to see what happens....

result :
the non matched mosfet is pulling about twice the current of the others...
no hum (well almost all gone -acceptable level)
offset 6.7mV

heatsink is warming up...

I will get to shops tommorow to purchase new 1 ohm resistor...

there is much to be learnt in putting these things together!!!

Ta

2nd February 2005, 02:39 PM	#1
george a diyAudio Member Join Date: May 2002 Location: oz	aleph 5 oscillating??? Hi all After much stuffing around i have seperated A5 power supply for the pcb's and output mosfets after upgrading heasinks to much larger size. However i now have other problems which I didn't have before!! 1. I now have approx 1V offset at speak terminals as opposed to approx 50mV previously. 2. I now have hum at ouput (even with now input wiring to pcb.) 3. Votages on pcb appear ok. 4 . voltage across 1 source resistor on one mosfet starts off ok then rises rapidly and the other mosfets current essontially drops to zero....ish. Is this one mosfet oscillating.???? I replaced it with another (matched ) and again voltage started off ok and then started to rise, is the mosfet dud , (it has 33ohm across gate to source... the ouptut mosfet are only a couple of inches from the pcbboard. any suggestions.???? thanks in advance cheers __________________ george a

2nd February 2005, 03:01 PM	#3
george a diyAudio Member Join Date: May 2002 Location: oz	Hi Jeremy They are the same as they are fed from same point I am using Mark Finnis PCb + mosfet pcb's BTW I removed 1 ohm source resistor and turned on to check other mosfet and the resistor R22 221ohm which goes from Q2 (Ztx450) to junction between source of mosfet and 1ohm resistor ended up smoking itself __________________ george a

2nd February 2005, 07:29 PM	#4
george a diyAudio Member Join Date: May 2002 Location: oz	Anybody ...please?? __________________ george a

2nd February 2005, 11:53 PM	#5
george a diyAudio Member Join Date: May 2002 Location: oz	please..?? BTW I don't have an oscilloscope to have a look at what's happening __________________ george a

3rd February 2005, 06:08 AM	#6
george a diyAudio Member Join Date: May 2002 Location: oz	anybody....please?? __________________ george a


	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

2nd February 2005, 02:53 PM	#2
kropf diyAudio Member Join Date: Dec 2002 Location: Illinois, USA	The negative rail of the front end has to be the same as the negative rail on the output stage. Jeremy

3rd February 2005, 07:52 AM	#7
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	The experts sleep sometimes __________________ /Per-Anders (my first name) or P-A as my friends call me

3rd February 2005, 08:46 AM	#8
george a diyAudio Member Join Date: May 2002 Location: oz	Yes Peranders , the experts do sleep sometimes. the problem is idiots like ME stay up all night worrying about what we've done wrong. Sweet dreams , good night - sleep tight regards from down under __________________ george a

3rd February 2005, 11:13 AM	#9
macka diyAudio Member Join Date: Dec 2001 Location: Australia	Sounds like a wiring fault, Post a few pictures so we can understand Macka

3rd February 2005, 12:48 PM	#10
george a diyAudio Member Join Date: May 2002 Location: oz	sort of a wiring fault macka looks like a dodgy 1 ohm resistor in the location that's blown 2 mosfets so far. I replaced the mosfet with a sacrificial non matching one and put in a 1.5 ohm resistor just to see what happens.... result : the non matched mosfet is pulling about twice the current of the others... no hum (well almost all gone -acceptable level) offset 6.7mV heatsink is warming up... I will get to shops tommorow to purchase new 1 ohm resistor... there is much to be learnt in putting these things together!!! Ta __________________ george a

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

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
PSU oscillating	apolon34	Power Supplies	3	24th June 2005 02:20 PM
Aleph-X oscillating. What to do?	AudioAngel	Pass Labs	15	26th March 2005 07:17 AM
Oscillating DoZ	rchua77	Solid State	1	30th January 2004 10:07 AM
Is your Aleph oscillating?	kenny_(00)_	Pass Labs	5	2nd September 2003 04:46 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