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Old 21st March 2013, 08:58 AM   #61
Witwe is offline Witwe  Germany
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Join Date: Dec 2010
Location: Schwerin
hmm....all 4 channels have the same problem with the Highpass...
Here is how the signals looks like with the scope at 5V/div:
Pin7 U300-U303 with the gainpot at minimum
Click the image to open in full size.

Pin7 with the gainpot at higher volume (1/3 turn cw)
U300-U301
Click the image to open in full size.

U302 (this seems to be the lowpass, right?)
Click the image to open in full size.

U303 (a little deformed)
Click the image to open in full size.

Pin1+7 with the gainpot at high volume (1/2 turn cw)
U300-U301 (is that normal????)
Click the image to open in full size.

U303 Pin1
Click the image to open in full size.

U303 Pin7
Click the image to open in full size.

or are the bias pots still set incorrectly?
I started with them at full ccw. (the amp draws 1,25A)
Then I slowly increased them till the amp draws a little more current (~1,29A)
And then I set it a little back to about 1,27A.
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Old 21st March 2013, 08:30 PM   #62
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Join Date: Nov 2003
Location: Louisiana
Do you have perfectly clean output from channels 1 and 2 with the crossover set to high-pass?

Has any work been done to the ch3/4 crossover section of the amp?
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Old 21st March 2013, 08:57 PM   #63
Witwe is offline Witwe  Germany
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Join Date: Dec 2010
Location: Schwerin
channel 1 and 2 are looking as bad as 3 and 4 with the high pass crossover set.

but at full range, all channels looks clean...
no I havn't done anything to the crossover, but I don't know if the previous owner has done anything. (my brother bought it from ebay and has never used the crossover)

should I check all the resistors for the correct value or can it be anything other?
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Old 21st March 2013, 09:17 PM   #64
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Location: Louisiana
There may not be any problem. Sometimes, crossovers will cause the signal to appear to be distorted when it's not. Does it sound OK in high-pass?
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Old 21st March 2013, 09:29 PM   #65
Witwe is offline Witwe  Germany
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Join Date: Dec 2010
Location: Schwerin
ok?
I will test it out tomorrow and Keep you informed.

and the Signal at Pin1+7 from U300-U301 is normal?
Click the image to open in full size.
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Old 21st March 2013, 09:34 PM   #66
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Location: Louisiana
Without the scope settings, it's impossible to determine if that's normal.
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Old 21st March 2013, 09:57 PM   #67
Witwe is offline Witwe  Germany
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Join Date: Dec 2010
Location: Schwerin
5v/div

with the volume a Little lower it Looks like this:
Click the image to open in full size.

this relates to all 4 channels.
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Old 21st March 2013, 11:43 PM   #68
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That is OK. You were over-driving the preamp section causing the op-amps to clip.
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Old 27th March 2013, 06:31 PM   #69
Witwe is offline Witwe  Germany
diyAudio Member
 
Join Date: Dec 2010
Location: Schwerin
back in the car the amp plays fine

thank you very very much for all your help and patience!!!!
My brother is very happy now. (2 month without music was a hard time for him =)
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