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Jun 27, 2013, 05:16 AM
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Preamp failure

Sadly, the home made preamp presented a defect since conversion to stereo that would prevent it from actually recording 2 channels. Over time, 1 of the channels often slowly fades out. Sometimes, it does nothing.

This didn't happen when both channels were directly connected to the XLR's. It only happened when a new switch was added to 1 of the channels to switch between a single XLR & dual XLR's. The fading happens to the 1 channel in both modes.

Toggling the switch temporarily makes the problem go away, before the channel fades out again after several minutes. It's not likely the pot. The switch is switching a very high impedance microphone input, making it very sensitive to contamination. It may not be practical. There is already another switch which switches between XLR's & RCA's, creating 2 points of contamination in the 1 channel.

Leading theory is a defective switch, which requires permanently soldering 1 mode in to test. If the problem can't be fixed in 2 months, there won't be a recording of the Delta IV heavy. It didn't have this problem when the switch first arrived.

The commercial ones all require 60Hz AC, probably because they benefit from isolation transformers.

Last edited by Jack Crossfire; Jun 27, 2013 at 02:33 PM.
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