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Old 19th July 2006, 01:28 AM   #11
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Ok, did some change to the board, I put in bc550c, I was using bc550b.
Now I did my setup like this: No load, and both inputs short to gnd.

For the left side I'm getting .47V at minimum. And for the right side .31V at maximum. potentiometer only give me about .04V of variation.I haven't check the DC offset so far.

I've checked again all the values of the resistors and everything is fine. Could it be something that is not match close enough?

There is definitely something wrong with this board.
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Old 19th July 2006, 12:58 PM   #12
DACMan1 is offline DACMan1  South Africa
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Is it normal for the absolute dc offset to be 10V at cold powerup? Mine is 10V and then drops.
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Old 21st July 2006, 12:52 AM   #13
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I finally found my problem, I had a bad connection between my mainboard and my driver board on the right side .That was the last time I'm using crappy connectors from local surplus.

But now I have both side that are having stable .5V across source resistor, tomorrow I'll adjust everything.

Thank you all for your help
Thierry
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Old 23rd July 2006, 05:50 PM   #14
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Hi, I have another quick question.

When I'm trying to adjust the amplifier if I set the bias to get .5V at the source resistor I'm getting 40mV of relative DC offset. If I'm working to get it down to 0V the reading I get on the source resistor is .512V on one side and .476V on the onther side.

My question is: Sould I aim for 0V of relative DC offset and live with the bias difference or the other way around? Or something in the middle?

Thank you
Thierry
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Old 23rd July 2006, 10:08 PM   #15
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally posted by bach2800
Hi, I have another quick question.

When I'm trying to adjust the amplifier if I set the bias to get .5V at the source resistor I'm getting 40mV of relative DC offset. If I'm working to get it down to 0V the reading I get on the source resistor is .512V on one side and .476V on the onther side.

My question is: Sould I aim for 0V of relative DC offset and live with the bias difference or the other way around? Or something in the middle?

Thank you
Thierry

40mV is practically nothing
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Old 23rd July 2006, 10:53 PM   #16
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Great!
Many thanks
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Old 24th July 2006, 11:39 PM   #17
jajabin is offline jajabin  United States
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Hi,

You are using Kari's boards, right?
If I am correct, there is an error on Kari's board. The IRF9610 on the top was reversed.
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Old 25th July 2006, 01:32 AM   #18
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Yes I'm using Kari's board. There are a few errors on the board, the reverse mosfet is one but nothing dramatics.
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Old 25th July 2006, 10:27 AM   #19
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Quote:
Originally posted by bach2800
Hi, I have another quick question.

When I'm trying to adjust the amplifier if I set the bias to get .5V at the source resistor I'm getting 40mV of relative DC offset. If I'm working to get it down to 0V the reading I get on the source resistor is .512V on one side and .476V on the onther side.

My question is: Sould I aim for 0V of relative DC offset and live with the bias difference or the other way around? Or something in the middle?

Thank you
Thierry

Hi,

you should set the bias the same for both sides (now you´ve got 10% difference) and then see what relative offset you get. If it´s under 100mV that´s allright. If not change the input diff pair for a better matched set.

Allways check the absolute dc and keep it around 0V for a warmed up amp (it will start between 5 and 10V from cold)

William
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Old 25th July 2006, 11:33 AM   #20
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Quote:
Originally posted by wuffwaff

Allways check the absolute dc and keep it around 0V for a warmed up amp (it will start between 5 and 10V from cold)

William

If it reaches 0V after a short warming-up time, it would be fine. . .
Err. . . the cold 5-10V are still there even with the "magic R". . . ?
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