Aleph 5 PSU problem please help?

xsnailx · 2nd March 2003, 04:50 PM

Please help i have some problems with my friends aleph 5 psu
When amplifier is on there is a reference +34v on both rails but when i power off this amplifier there is 3v on minus to gnd rail and +10 volt on the second as senn on attached picture
is the caps bad or is it a normal behavior
is a bank of caps destroyed?
besides that amplifier woks extremly well

wuffwaff · 2nd March 2003, 05:30 PM

Hi,

I think this is normal cause the amp won´t work under +10V (something to do with the 9,1V zeners).

If you don´t like this just put some bleed resistors over the caps or use the on/off led for this purpose.

william

xsnailx · 2nd March 2003, 06:10 PM

wuffwaff, thank you for a quick reply
i dont know if you understand me good
10 and 3 v are measured after turnning off the mains - taking plug from the wall
i just dont like that fact that there is such a difference it apperars strange to me and is it possible that aleph draws more from - rail?

Tube_Dude · 2nd March 2003, 06:19 PM

HI xsnails!

The advice that wuffwaff of to put the bleeder resistors in paralel with the caps is a very good one...and it will resolve your problem!

regards

Jorge Santos

xsnailx · 2nd March 2003, 06:29 PM

ok will try to do so
should i experiment with walue until i reach near equal values?
or doing only simple exchange between caps i meen put some from one rail to another will do too?

Tube_Dude · 2nd March 2003, 06:41 PM

D'ont make any exchange between capacitors!

Put a 10 KOhm resistor betwen the + and ground and another 1ok resistor between - and ground at the output of the power suplly!

A half watt resistor will doo because the maximal current will be 3.4 mA!

And forget!!...and enjoy the sound!!!

Everything is OK

cheers

Jorge santos

grataku · 2nd March 2003, 07:51 PM

snailx
maybe you have a problem... So this voltage is measured immediately after the amp is powered off? then I am guessing that the after afew secs everything goes to 0, right?
If the amp has a load, the two half of the output pair can behave as independent entities, if the CS mosfet bias is cut off more rapidly than the gain mosfet bias you would end up with such huge differences. If you think one of your caps is shot put a couple of 8 ohms resistors as the load instead of the amp and watch what happens. If you still see this behavior then one of the caps maybe gone.
You can also check out the dc offset between output and gnd or monitor the source drop after turn off with a couple of voltmeters, see what it does.
IMO is no problem unless you hear weird noises of measure a huge dc offset at turn-off.

xsnailx · 3rd March 2003, 06:38 AM

Ok as i said before amp works very well
sound is great

Grataku, yes you are right it is measured jus after turn off and every thing goes to 0
cannot do much more now cos iam in work for next 7 hours

Thanks for help !!!!

Mark A. Gulbrandsen · 4th March 2003, 12:08 AM

Aleph amplifiers always seem to discharge the caps unevenly. Sometimes this will cause a turn off thump heard in the speakers. Just installing the bleeder resistirs will take care of this. Some experimentation may be necessary as both resistirs will be differing vaules to get the rails to come down together. The more capacitance you have in the supply, the worse the thump will be.
Mark

xsnailx · 4th March 2003, 06:59 AM

there is a 6*47000uf capacitance in the supply
turn off thump is rather small
so i will try with the resistor

2nd March 2003, 05:30 PM	#2
wuffwaff diyAudio Member Join Date: Aug 2001 Location: Ingolstadt Germany	Hi, I think this is normal cause the amp won´t work under +10V (something to do with the 9,1V zeners). If you don´t like this just put some bleed resistors over the caps or use the on/off led for this purpose. william __________________ een ooievaar is geen konijn want zijn oren zijn te klein!

2nd March 2003, 06:10 PM	#3
xsnailx diyAudio Member Join Date: Dec 2002 Location: Poland, Cieszyn	wuffwaff, thank you for a quick reply i dont know if you understand me good 10 and 3 v are measured after turnning off the mains - taking plug from the wall i just dont like that fact that there is such a difference it apperars strange to me and is it possible that aleph draws more from - rail? __________________ Boleslaw Zaras

2nd March 2003, 06:19 PM	#4
Tube_Dude diyAudio Member Join Date: Mar 2002 Location: Aveiro-Portugal	PSU Problem HI xsnails! The advice that wuffwaff of to put the bleeder resistors in paralel with the caps is a very good one...and it will resolve your problem! regards Jorge Santos

2nd March 2003, 06:29 PM	#5
xsnailx diyAudio Member Join Date: Dec 2002 Location: Poland, Cieszyn	ok will try to do so should i experiment with walue until i reach near equal values? or doing only simple exchange between caps i meen put some from one rail to another will do too? __________________ Boleslaw Zaras

3rd March 2003, 06:38 AM	#8
xsnailx diyAudio Member Join Date: Dec 2002 Location: Poland, Cieszyn	Ok as i said before amp works very well sound is great Grataku, yes you are right it is measured jus after turn off and every thing goes to 0 cannot do much more now cos iam in work for next 7 hours Thanks for help !!!! __________________ Boleslaw Zaras


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2nd March 2003, 06:41 PM	#6
Tube_Dude diyAudio Member Join Date: Mar 2002 Location: Aveiro-Portugal	D'ont make any exchange between capacitors! Put a 10 KOhm resistor betwen the + and ground and another 1ok resistor between - and ground at the output of the power suplly! A half watt resistor will doo because the maximal current will be 3.4 mA! And forget!!...and enjoy the sound!!! Everything is OK cheers Jorge santos

2nd March 2003, 07:51 PM	#7
grataku diyAudio Member Join Date: Dec 2000 Location: -	snailx maybe you have a problem... So this voltage is measured immediately after the amp is powered off? then I am guessing that the after afew secs everything goes to 0, right? If the amp has a load, the two half of the output pair can behave as independent entities, if the CS mosfet bias is cut off more rapidly than the gain mosfet bias you would end up with such huge differences. If you think one of your caps is shot put a couple of 8 ohms resistors as the load instead of the amp and watch what happens. If you still see this behavior then one of the caps maybe gone. You can also check out the dc offset between output and gnd or monitor the source drop after turn off with a couple of voltmeters, see what it does. IMO is no problem unless you hear weird noises of measure a huge dc offset at turn-off.

4th March 2003, 12:08 AM	#9
Mark A. Gulbrandsen diyAudio Member Join Date: Sep 2001 Location: Salt Lake City	Aleph amplifiers always seem to discharge the caps unevenly. Sometimes this will cause a turn off thump heard in the speakers. Just installing the bleeder resistirs will take care of this. Some experimentation may be necessary as both resistirs will be differing vaules to get the rails to come down together. The more capacitance you have in the supply, the worse the thump will be. Mark

4th March 2003, 06:59 AM	#10
xsnailx diyAudio Member Join Date: Dec 2002 Location: Poland, Cieszyn	there is a 6*47000uf capacitance in the supply turn off thump is rather small so i will try with the resistor __________________ Boleslaw Zaras

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