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Old 15th September 2005, 05:05 PM   #1
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Default DC protection for leach

I have made no simulation or test yet but I would like to have opinion on this circuit configuration
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Old 15th September 2005, 05:08 PM   #2
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here is the picture
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Old 15th September 2005, 06:22 PM   #3
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Me again.
Sorry inverting & non inverting input of op-amp are reversed
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Old 19th September 2005, 07:56 PM   #4
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I did no test or make simulation but I found found that the integrator with no close loop will always fire after a period of time. So I am going back to the drawing table.
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Old 19th September 2005, 08:32 PM   #5
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Have you tried connecting a 1 meg resistor in parallel with C3?

It works at higher frequencies. As long as the other resistors are relatively low in value (less than ~50K ohms), it may work for your circuit.
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Old 19th September 2005, 09:26 PM   #6
jaycee is offline jaycee  United Kingdom
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I guess this is a crow-bar circuit to blow the fuses should DC appear.

The detector seems overcomplicated to me. You could achieve the same effect with 4 diodes, an R/C filter and a few transistors to fire the crowbar. This would have the advantage that you can run it from the poweramp rails without needing any +-15v supply for the opamps.
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Old 19th September 2005, 11:13 PM   #7
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A resistor across C3 is a great idea, I did not see this one by myself but after a quick analysis it is clear that he resistor will limt the gain at low frequency and will solve the run away problem. tanks Perry

+15V an -15V could be a problem for most but my amp is build with old transformer from few IBM PROPRINTER stuff and there is 2 10 volts AC tap in the powersupply with 2 diodes and 2 caps I will have a non regulated supply for the OP amp. Thanks Jaycee for the hint
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Old 22nd September 2005, 06:53 PM   #8
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I made a few simulation and the new circuit is below

triac optocoupler led & stuff tig at 3.5 volts

Response of filter including op-amp stage

dc + 14 db
3Hz + 10db
1.6 Hz 0 db
4Hz -10db
8.5Hz -20db
16Hz -30db
30Hz -40db

system should trig at 0.7 Volt DC
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Old 22nd September 2005, 09:01 PM   #9
Quattor is offline Quattor  France
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This type of circuit has to perform in two quite opposite directions. First, it should detect only DC voltage - thus removing everything AC at it's input. Secondly, it should react as fast as possible since you don't want to turn your speakers into heaters and melt them down in a matter of miliseconds. Improving one, degrades the other one. Of course, you want to react on rather low DC levels - 0.6 - 0.7 V (matches with the need for speed).

Attached circuit has performed quite well in all sorts of situations. Don't mind +33 V reference there. You can use different voltages as well. My suggestion is to use +12 V and to tie up CMOS 40106 or CMOS 4093 (Schmitt-triggers) at it's output. Works like a charm every time

Best regards,
Nick
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