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The Allen & Heath GL4 is a analog live mixing console released in the mid-1990s.

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Audio mixer not enough phantom power current?

When I plug in several dynamic and condenser microphones into my 32-channel 1995 Allen & Heath GL4 mixer, a specific large diaphragm condenser (LDC) microphone drops out and turns into white noise.

  • The mic in question works fine on modern audio interfaces
  • The only solution is to replace it with an small diaphragm condenser (SDC), and I was able to continue my drum recording session.

The particular LDC mic will work on the AH mixer only if it's the only microphone being powered, regardless of which channel the LDC mic is attached. However, when other channels are powered, even without mics attached in the other channels, the prior LDC drops out into white noise.

The Power Supply Unit has been recapped, about 4 large capacitor and 1 medium capacitor, and 2 smaller ones. -- save for some very small capacitors that do not look like they are blown. The problem described was already noted even for the recapping.

Maybe someone has encountered this same problem and knows where to start looking with regards to this mixer?

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A friend of mine had a mic which I don't remember which type that always messed him up we created a breakout to test it checking the voltage as well as the polarity as it turned out it was mis-wired internally.

Can you create or have a way to tap the lines using a meter to see what's happening and comparing it to your other units? Maybe that will help you discover the fault.

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In general the channels deliver 3.5 mA of current when activated individually with 48V. But when other channels are activated, the current dips then slowly creeps back up, but only up to 3.15 mA or so. When ALL channels are activated, the current is down to a tad above 2.0 mA. Still haven't had the time to open the board to where to power feeds in, to check anything.

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Ryan Madrid will be eternally grateful.
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