Completed aleph J --loud cracking sound on switch off

[kp93300]

Hi All,
I need help to solve the problem.
I just completed the aleph J and noted a very loud cracking sound through the loudspeaker on switch off of the power supply.
It is very quiet on switch on and no hum at all.
The dc offset at output is less than 0.2 V but swing to about 1 to2 V on powering down.
I am using a CLC type of line filtering with about 200000UF caps. The L is wound on a EI transformer , diy type.
I also use about 11 uF of motor start non polar caps at the last stop.
Could this be the problem ?

appreciate all the help

kp93300

 

[John Caswell]

Cracking sound

Hi kp9etc,
Sounds very much like arcing inside the power switch. Suggest you put snubbers/switch click suppressors across each section of the switch, consisting 0.1µF "Y" type capacitor in series with 100-120R resistor, or buy them ready made from RS or farnell.

John

 

[Zen Mod]

you can check John's idea with simple test - instead of using mains switch to power off amp - just plug power cord from wall .

 

[John Caswell]

Cracking

Good idea Wilson, didn't think about that one, Capt. Mainwaring

John

 

[kp93300]

you can check John's idea with simple test - instead of using mains switch to power off amp - just plug power cord from wall .

To power off, I pull the power cord from the ac receptacle and the problem persisted.
kp93300

 

[Zen Mod]

pictures , please

 

[kp93300]

Hi kp9etc,
Sounds very much like arcing inside the power switch. Suggest you put snubbers/switch click suppressors across each section of the switch, consisting 0.1µF "Y" type capacitor in series with 100-120R resistor, or buy them ready made from RS or farnell.

John

Will a 1/2 w resistor be ok ?
Can I use x2 rated ? Is the value of 0.1uF critical ? Smaller and larger value ?

thanks
kp93300

 

[Zen Mod]

considering this :

To power off, I pull the power cord from the ac receptacle and the problem persisted.
kp93300

this will not help :

Will a 1/2 w resistor be ok ?
Can I use x2 rated ? Is the value of 0.1uF critical ? Smaller and larger value ?

thanks
kp93300

problem is somewhere else , not in power switch

 

[kp93300]

pictures

These are some pictures of the aleph j that I build.
The transformer is in another box.
The pre is J310 and Lightspeed clone as the attenuator.
hope i can find some pointers in troubleshooting this problem.

kp93300

 

[kp93300]

more pictures

Some more pictures of the build

 

[Zen Mod]

is it happening on both channels , or just one ?


I see that you have dedicated CLC for each channel , but I don't know rest

describe topology of PSU , starting from xformer

 

[kp93300]

power supply for aleph J

Hi Zen Mod,
There is a slow start board and CL 60 before the 500W 18 0 18 0 V ac transformer.
One transformer for both channels.
C L C filtering. The trans and first C is shared with another amp---F5. There is no such problem with F5.
The L( inductor ) and C is recently diyed for the AlephJ. I have one L for the +Ve and one L for the -Ve. The + and- ve rails are shared with both channels.
The amp sees 21 V dc on load and measure the same for both channels.
many thanks

kp93300

 

[kp93300]

One more thing, the load noise happens for both channels on power down.Lasted about 1 sec.
kp93300

 

[jmsent]

FYI, the stock First Watt Aleph J also does this, so it's likely inherent in the circuit.

 

[Zen Mod]

mea culpa - I didn't had opportunity to hear/use stock A J , neither to make clone of it .

in any case - if there is any power down noise in original one , it must be non-harmful

 

[Rodeodave]

Don't most Alephs do that? There were various discussions on that in the past. I believe it has something to do with the +/- rails not draining equally fast when the power is cut. Maybe different value bleeder resistors can minimize the effect. I didn't bother with my Mini Aleph though since my speakers seemingly are okay with it.

 

[jmsent]

My old Aleph 0's are pretty quiet at both turn on and turn off. I also have a new Aleph J2, and that one is also transient free.

 

[kp93300]

Thanks you all for the replies.
I disconnect the speaker cable when i powered off to avoid the problem even though this has no effect on the speaker.
kp93300

 

[frags]

I'm using these speaker protection modules rated at 30A in my Aleph J:
Speaker Protection Module -- Mono Type One Channel x2 on eBay.ca (item 270673874283 end time 01-Jan-11 14:37:15 EST)
No cracking sound at power on/off at all.
Disconnecting speaker cables each time is sort of extreme.