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Old 20th November 2009, 05:00 PM   #6001
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Quote:
Originally Posted by bluewater View Post
Would anyone have any input on why I would have 500mV pushing out my outputs on one of my channels?
Are you shure there is no dc at the input?
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Old 20th November 2009, 08:48 PM   #6002
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the input is isolated from anything and the two output transistor are cool to the touch.
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Old 20th November 2009, 08:55 PM   #6003
CBRworm is offline CBRworm  United States
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Quote:
Originally Posted by bluewater View Post
the input is isolated from anything and the two output transistor are cool to the touch.
That can't be good. Touching a cold amp is like holding a dead fish.
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Old 20th November 2009, 09:28 PM   #6004
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Bluewater, have you confirmed that both pots are at zero and re started the bias process from scratch?
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Old 20th November 2009, 09:57 PM   #6005
tinitus is offline tinitus  Europe
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And prove sticks have been connected in the right place when adjusting?
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Old 21st November 2009, 12:42 AM   #6006
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thank you for all the reply's.
no I haven't tried starting from zero mostly because it was working fine before this happened. I not sure if starting with the pots is the right course just yet.
tinitus, what do you mean by sticks?
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Old 21st November 2009, 01:05 AM   #6007
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by bluewater View Post
tinitus, what do you mean by sticks?
Oh, sorry
I wrote "prove" sticks, and it should have been "probe" sticks
Those things to connect multimeter to amp board
Isnt that what they are called?

What I was asking
Do you measure the right way?
Is multimeter used properly?
Connection point, meter setting etc.
Are your probe sticks in good condition?
I have to resolder mine frequently
Not the most reliable things
And sometimes a meter works fine with one setting and not with some other setting, cheap ones ofcourse, but thats what most of us can afford, but may not be completely reliable either

Last edited by tinitus; 21st November 2009 at 01:16 AM.
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Old 21st November 2009, 01:14 AM   #6008
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they work fine and are in good shape. When adjusting the dc offset I connected them to the output and the output ground.
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Old 21st November 2009, 01:20 AM   #6009
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by bluewater View Post
When adjusting the dc offset I connected them to the output and the output ground.
I dont think you should do that without monitoring bias at the same time
As I understand it, its possible to "find" a bias a point where DC is low
But you cannot just turn bias pot to the lowest DC
It should be done carefully, bit by bit
And never turn bias pot only looking at DC
Output devices can go dead in a second without heatsink even getting hot

But now I talk about something Im not sure about, as I havent built my F5 yet

But I do remember to have done something similar, turning a trim pot without anything happening
Amp went dead before I realised I had been looking at the wrong meter setting

Last edited by tinitus; 21st November 2009 at 01:32 AM.
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Old 21st November 2009, 01:23 AM   #6010
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While adjusting the offset I had another multimeter monitoring the voltage drop on r11 or r12.
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