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Old 27th October 2005, 09:43 AM   #1
Stabist is offline Stabist  Slovenia
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Default MiniA strange behaveur

Hi,

finnally finished (almost) MiniA - tested it - it plays. Quite well indeed )

BUT - because of some noise in speakers (buzzing and annoying when no music) - I've decided to play with grounding a bit more ... And now I have strange powering on problem (

The layout looks:
- 2 mono home made PCBs (not from group buys) - original for Aleph5
- each at his heatsink
- common PSU - 1 trannie 12V-0-12V + 2x46.000uF/20V SPrague 36D caps
- kind of a star ground in the middle od the PSU caps.

1st attempt:
- to that star ground I connected signal gnd from input RCA, gnd for speaker output, connection to middle tap of the trannie and gnd for each PCB - so PCB had only 1 GND connection
buzz (
2nd attempt:
- I've moved the signal gnd form inputs to PCB - I have 2 different GND lots on PCB - one for PGNG and one for SGND - and so I connected them seperately
buzz ((
3rd attempt:
- SGND and PGND on PCB soldered together to the same lot
AND NOW - when starting up the amp - in the left channel for couple seconds -14,5V!!!!!!! at speaker outputs?!??!?!? (that's like full rail voltage) and then slowly falling down to few mV ... The other channel - a "power on short term spike" and normal operation ... ?!?!?
OK, resoldering back to "2nd attempt" version - problem remains?!?!?
Then I decided to discharge PSU caps by additional resistor - (without that the voltage at the output with amp shut down (but no load) settles at around 2,8V - and power it back - normal - short spike of few volts and down to 30mV ...
Power off and back on - again - 14,5V that stays for few seconds and then it normalizes ...?!?!?!?

OK, it was late - went to bed - this morning before going to work I tryed about 10 times
power on/off cycle - nothing - works normal - short spike (power on thump) and everything is OK ?!?!?!?

What is/was happening with my MiniA?!?
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Old 27th October 2005, 05:40 PM   #2
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Hi,

try to test it with a 8 or 4 ohm load. If the peak goes down to 3-3,5V (from 14V) everything is normal.
I donīt think the earthing experiments have anything to do with it. Maybe you just didnīt notice it before......


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Old 27th October 2005, 09:19 PM   #3
Stabist is offline Stabist  Slovenia
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Hi!

I just wonder - I'm a stupid or .... I gues I know what I've done wrong.

I have "stereo" power supply - and both channels were attached to it - but I connected test speaker unit to only one channel - and so - when powering up - a lot of strange stuff appeared - sometimes this 14V peak, sometimes normal ... sometimes something in between etc ...

Then I disconected the other channel from PSU - everything worked OK ...
Connected back (still without speaker) - again ...

But after adding another speaker to the other channel - after around 30 attempts - everytime I get small almost unoticable "thump" - and I measure around 1V of spike ...

SO!! - I guess it was just that the amp was not simetrical loaded - and because of common PSU - the result was that unpredictable powering on??
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Old 27th October 2005, 09:44 PM   #4
Stabist is offline Stabist  Slovenia
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Gee .. I think I now confirmed also the situation when poor speaker can get full voltage at power on - if the amp was turned on and off without speakers, shortly after the speakers were connected and amp is again powered on - then sometimes this occurs ... And sometimes not ...

SO - avoid such strange tests ...

Btw - I don't have in mind I noticed this with Aleph5 ...
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