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Old 20th September 2008, 11:32 AM   #11
Dxvideo is offline Dxvideo  Turkey
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Right... And this is why C6 is there for. Is it?
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Old 20th September 2008, 11:36 AM   #12
AndrewT is online now AndrewT  Scotland
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Quote:
Originally posted by Dxvideo
Right... And this is why C6 is there for. Is it?
no.
Fit DC blocking/servo at source.
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Old 20th September 2008, 11:38 AM   #13
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Hi Andrew,
The problems shows up at LF. Part of the problem is that as with most things there are compromises to be made. Having very long time constants may seem the solution, but waiting 20 or 30 secs for the loop to stabilize isn't practical.
Squarewave testing at LF shows up the effect well.
I looked at all this in my amp, and found this out by experiment. Another DIY member who built the amp tried adding a second time constant and found as I had that the LF distortion rose and stability suffered.
You know me -- I wouldn't be happy simulating it - would have to at least breadboard it and see
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Old 20th September 2008, 11:38 AM   #14
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At source? How?
In iPod, in CDP or in my soundcard? (these are my all treasure )
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Old 20th September 2008, 11:39 AM   #15
AndrewT is online now AndrewT  Scotland
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Quote:
Originally posted by Dxvideo
At source? How?
In iPod, in CDP or in my soundcard? (these are my all treasure )
measure and/or examine them.
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Old 20th September 2008, 11:43 AM   #16
Dxvideo is offline Dxvideo  Turkey
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I have the measurement results already..
Creative XFI soundcard ~100mV (I dont know the reason)
iPod ~1mV
CDP ~10mV
So CDP and soundcard is very dangerous at the moment. And I am using 2u2 MKP s before my present preamp (single stage LM4562 with 3X gain)
So if a general solution is needed: The C6 must be stay there.
Just a question; whats wrong with C6? (except its value of course)
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Old 20th September 2008, 11:46 AM   #17
Mooly is offline Mooly  United Kingdom
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Ozgur
Whats the problem with the OPA627 on it's own. Do as Andrew suggests and up the input filter time constant. Just increase R8 to 330 k or so and keep your 0.68mfd. Its a FET OpAmp, you don't need worry over unequal input resistances anyway
That it then
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Old 20th September 2008, 11:48 AM   #18
AndrewT is online now AndrewT  Scotland
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http://www.diyaudio.com/forums/showt...50#post1283350
for a fuller explanation of the issues.
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Old 20th September 2008, 11:49 AM   #19
Mooly is offline Mooly  United Kingdom
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Quote:
Originally posted by Dxvideo
I have the measurement results already..
Creative XFI soundcard ~100mV (I dont know the reason)
iPod ~1mV
CDP ~10mV
So CDP and soundcard is very dangerous at the moment. And I am using 2u2 MKP s before my present preamp (single stage LM4562 with 3X gain)
So if a general solution is needed: The C6 must be stay there.
Just a question; whats wrong with C6? (except its value of course)
You need to measure these with a low pass filter on your DVM. Say a 10 k and 1 mfd. There could be a lot of HF "rubbish on the outputs which confuses things.
Can I have my dinner now please
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Old 20th September 2008, 11:49 AM   #20
Dxvideo is offline Dxvideo  Turkey
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Sure...
Its a simple solution. It seems I will have a DC blockage on gainclones input.. So I dont need to worry about it.
But if OPA627 gets unstable situation by the meaning of DC offset and this offset goes to my potentiometer and after a while my potentiometer have some problems because of that DC offset?
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