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Old 20th September 2008, 11:51 AM   #21
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Quote:
Originally posted by Mooly


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
Dinner ? At this time? Are you in Japan?
Anyway, bon apetite..
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Old 20th September 2008, 11:53 AM   #22
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Quote:
Originally posted by AndrewT
http://www.diyaudio.com/forums/showt...50#post1283350
for a fuller explanation of the issues.
Of course..
The old topic! I will build a DC Servo, sooner or later!
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Old 20th September 2008, 11:54 AM   #23
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Quote:
Originally posted by AndrewT
http://www.diyaudio.com/forums/showt...50#post1283350
for a fuller explanation of the issues.
As Capain Mainwaring would say " Ohh, haven't got time for all that now "
It's dinner time !! Hungry!! Need feeding !!
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Old 20th September 2008, 11:55 AM   #24
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Lunch then
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Old 20th September 2008, 12:00 PM   #25
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Bon appetite again..
I am going to home now, for a lunch of course.. I will measure my OPAs DC offset (with inputs shorted) after the luch and will discuss the potential potentiometer events with that offset..
See.
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Old 20th September 2008, 03:31 PM   #26
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My OPA s output is 0.1mV... Without offset trim and while inputs shorted.
Does it cause any potentiometer harm in long term?
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Old 20th September 2008, 05:15 PM   #27
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Hi,
No problem at all ? If you null it even that will reduce to zero, but be careful. It's not always straightforward measuring such things, and I would again use a low pass filter on the output to get a "truer" reading.
Does your meter actually read 0.000volts with the probes shorted ? If you swap the meter leads round does it show -0.1mv or something different
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Old 20th September 2008, 05:38 PM   #28
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Mad thoughts as you do, not just from todays posts but going way back.
Regarding power amps -- have the error signal fed to a sample/hold circuit that only operates at switch on for a minute or so and then say every 5 mins after that, just for long enough for a new error voltage to be aquired. Problems, well I suppose if there were significant drift of the offset then each time it corrects that could be audible.
Captain Mainwaring again " Your getting into the realms of fantasy now Mooly "

Next ? (Back to the preamp now) Use the output of the servo to correct the OPA via it's offset null terminals. That could interesting, perhaps setting a deliberate error up on one pin and correcting via the other, or perhaps some Opto scheme.

But I think with 0.1mv untrimmed we won't bother today.

It's Tea Time -- and not a moment too soon
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