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In Reply to: RE: HELP: DC at the input of an old MA1's. posted by MaceEar on December 13, 2007 at 01:55:01
I now understand that the condition does not occur after the B+/B- supplies are turned on, but only before you do that. Also, the condition is detectable with no input connected and seems to have no affect on sonics when finally the amps are fully on and warmed up. I presume that your units were built to accept 230V, so we can discount that as a cause of the "problem" (if it IS a problem). I am stumped. Are you sure this is a true DC voltage? Did you measure AC voltage too? Lets ask Ralph.
As for your observation about the input resistance (500K ohms), that does seem high. I don't know how your amps are wired, but many Atma amps have a switch to convert from "Hi Z" to "Lo Z" input. The high Z input should read around 200K ohms, from pin 2 to pin 3. (There are two 100K resistors, one each going from pin 2 to ground and pin 3 to ground. The way you are measuring, each meter would see 100K ohms.) But I cannot say that maybe your amps have 250K ohm resistors between each hot pin and ground, so your 500K measurement is to be expected. If your amps have a "Lo Z" switch, or if your amps are hard-wired for a low Z input, then you would see typically 600 ohms between pins 2 and 3. If you are not using an Atma-sphere preamp, then you are probably better off with the hi Z input, and 500K ohms is "OK" functionally.
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