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Old 29th January 2009, 12:48 PM   #101
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You're starting to sound like the Self quoting whip.
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Old 29th January 2009, 01:02 PM   #102
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally posted by jacco vermeulen
You're starting to sound like the Self quoting whip.

kwayzee dutchie ;
that's because ya're absent
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Old 29th January 2009, 01:05 PM   #103
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Default z1,z2,z3,z4

Looking at the picture in post 88 and considering:
(ref a2serv0.pdf, original service manual)

-You used the protective zeners z1..z4.
-You are testing with unbalanced input
-You did not connect -IN to ground during testing.
-You heard a pop

I would check the input zeners, especially z1 or z3.
I ran a sim to check my suspicion (z1 shorted) and the result is
very similar to your picture in post 88.

You could even consider removing the protective zeners
temporarly and test. Make sure you do connect all equipment
before power on of the amp.

regards

PS
In graph
Green is input 1.5Vp
Red is output
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Old 29th January 2009, 01:17 PM   #104
Bakmeel is offline Bakmeel  Netherlands
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Default Re: Re: Re: Low Frequency settle

Quote:
Originally posted by Zen Mod

first - correct R19 that you have Papa's values of Iq ......... 0,5A per each mosfet


fiddle with R11 in same time to preserve zero offset on output

then check AC gain
R19 is now around 80k. --> I_CCS = 500mA

Changing R11 doesn't change zero offset, but it's down to 50mV now

Clipping is still there when input exceeds 600mV or so.

Y'know, by now I have checked, measured and/or replaced almost every component on this PCB. There really aren't that many, and still the behaviour remains.

I'm going to leave it at this, and tomorrow I will bring in the Front end PCB of the still working amp. That way I'll have some comparison.
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Old 29th January 2009, 01:24 PM   #105
Bakmeel is offline Bakmeel  Netherlands
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Default Re: z1,z2,z3,z4

Quote:
Originally posted by rtirion
Looking at the picture in post 88 and considering:
(ref a2serv0.pdf, original service manual)

-You used the protective zeners z1..z4.
-You are testing with unbalanced input
-You did not connect -IN to ground during testing.
-You heard a pop

I would check the input zeners, especially z1 or z3.
I ran a sim to check my suspicion (z1 shorted) and the result is
very similar to your picture in post 88.

You could even consider removing the protective zeners
temporarly and test. Make sure you do connect all equipment
before power on of the amp.

regards

PS
In graph
Green is input 1.5Vp
Red is output
Z1 - Z4 were one of my first suspects... Quite right, especially because clipping starts when the unbalanced input exceeds 0.6V.. precisely one PN junction.

However, I have removed Z1 and Z3 in post 74, and they haven't been back ever since...
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Old 29th January 2009, 01:40 PM   #106
Zen Mod is offline Zen Mod  Serbia
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just in case ........ repeating what rtirion already wrote - running unbalanced - did you ground neg input ?
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Old 29th January 2009, 01:52 PM   #107
Bakmeel is offline Bakmeel  Netherlands
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No. I didn't.

Grounding actually worsens the problem. Clipping then starts at 300mVp-p input.

-edit-
But why ground -IN? there is a parallel 10k to ground there? (R5)
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Old 29th January 2009, 01:58 PM   #108
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally posted by Bakmeel
No. I didn't.

Grounding actually worsens the problem. Clipping then starts at 300mVp-p input.

-edit-
But why ground -IN? there is a parallel 10k to ground there? (R5)

you're right ;

R5 is there as foolproof part
I didn't know did you installed it or not .

did you checked all resistor values ..... ?
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Old 29th January 2009, 02:01 PM   #109
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Also just in case, I didn't take the time to read everything:
The Drains of the diff-pair are well isolated from each other I hope? (Mica)
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Old 29th January 2009, 02:16 PM   #110
Bakmeel is offline Bakmeel  Netherlands
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Yep... See picture in Post # 17. Silpads and nylon nuts & bolts. Verified and checked... the drains are isolated.
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