Joseph Meditz
From:
Sierra Vista, AZ
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Posted 18 Apr 2012 6:56 pm |
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I'm looking at the +/- 15V preamp power supply. It is fed from a separate, lower voltage, winding than the PA PS. I measure about 35 Vac or 17.9 Vac each side.
Right before the positive regulator there is a 700 Ohm 5W power resistor going to ground. What is its purpose?
My guess is that it is there to put a load on the transformer to bring the input AC voltage down.
There seems to be a lot of concern about that since R85,6,7&8 appear also to be there also to knock down the level of AC.
Thanks,
Joe |
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Joseph Meditz
From:
Sierra Vista, AZ
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Posted 21 Apr 2012 2:43 pm
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Well, after thinking about this I feel that the 700 Ohm 5W resistor is for slow turn on to avoid turn on thump. Once I calculated the RC time constant it clicked in my mind. The time constant is 0.7 sec., and I've noticed that the red LED lights up a couple of seconds after the amp is turned on.
Since I slipped whilst probing and shorted the -15V regulator, until I put in an order I won't be able break anything else for awhile. |
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