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Old 27th January 2016, 10:00 PM   #1
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Default lm3875 at 94V

hi i dont have enough parts at stash,run out of good transformers and hi curent regulators ,and in sort of hurry to finish amp.at +-45v dc is it better to drop 10v with 2sc1943, 2sc5200 or put them in output(dont care i need pair more i have stash) ,sort of using 3875 as first stage but on 94v still ? i know neither solution is good but i need to have spare amp in few days from now,so cant wait for parts to arrive.

i think is lot better to put in output but want to make sure i didnt miss something.
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Old 28th January 2016, 12:43 PM   #2
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ok this should work, i will try this afternoon to make then post if it is working and why not,but i will use 3875
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Old 28th January 2016, 01:26 PM   #3
AndrewT is offline AndrewT  Scotland
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Absolute maximum ratings are 94V rail to rail when no signal is present and 84V rail to rail when a signal is present.

Your measured 94Vdc may not be worst case.
How high could that go when mains is at it's highest?

I suggest that you build a non feedback voltage regulator using a Zener and emitter follower (Pass has examples) to bring your supply down to +-40Vdc, or lower.

A capacitance multiplier could also drop significant voltage to enable your chipamp to survive.
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Old 28th January 2016, 07:36 PM   #4
tomchr is offline tomchr  Canada
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Quote:
Originally Posted by AndrewT View Post
Absolute maximum ratings are 94V rail to rail when no signal is present and 84V rail to rail when a signal is present.

I suggest that you build a non feedback voltage regulator using a Zener and emitter follower (Pass has examples) to bring your supply down to +-40Vdc, or lower.
+1

Here's a good intro to zener regulators: Voltage Regulators, Different types, Working principle, Design

Tom
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Old 28th January 2016, 08:03 PM   #5
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hi, now in another doubt, option 1 or option 2
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Old 29th January 2016, 08:44 AM   #6
AndrewT is offline AndrewT  Scotland
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Left works. Right does not work.
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Old 29th January 2016, 11:34 AM   #7
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sry , my mistake i was in hurry and just made mirror of top image.

will this work
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Old 29th January 2016, 11:37 AM   #8
AndrewT is offline AndrewT  Scotland
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Now both work.

Did you look at Pass?
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Old 30th January 2016, 04:10 PM   #9
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it burned resistor on negative side, and for few seconds there was 1.5v on output. i cant find Pass labs version of this.
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Old 31st January 2016, 05:29 PM   #10
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well managed to put 84 volts on -ve somehow, and burned both 3875 ,still not sure how. found stk module which works on 90+ volts.
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