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Old 15th February 2009, 04:09 PM   #1
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Default Behringer PMH300 noisy phantom

I noticed last year that the first two channels on my PMH3000 had intermittent crackles on them when using phantom powered mics. If dynamic mics are connected and the 48v switched off all is ok. All other channels are fine even with phantom powered mics.
This year channel 2 has got much worse and is completely unusable with the 48v switched on.
Has anybody else had similar problems ? I have disassembled the unit and tried to swop the larger capacitors around in the front end (between ch2 and ch3) but had no joy at tracing the source of the noise,
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Old 19th February 2009, 01:40 PM   #2
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Does anyone have a schematic diagram for the input stage of a channel on this mixer to show the phantom powering ?
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Old 19th February 2009, 04:27 PM   #3
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Location: North Derbyshire
I've got an MX802 circuit, but really theres very little in phantom powering - just two 6K81 resistors feeding 48V to the input pins.

Perhaps the coupling capacitors from the input to the ampliifer are leaky?, they have to block the 48V DC.
Nigel Goodwin
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Old 18th March 2009, 01:39 AM   #4
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Thanks for your reply.
Yes Ive had a closer look and see what you mean. The curcuit is very simple around the XLR. Ive pulled the two 47uF/50v caps that couple the XLR to the mic input and some more caps are on order.I'll let you know how I get on
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