DBX 1231 EQ Ground Hum Problem

[michaelyallop]

Bit a strange one. We have a DBX 1231 EQ. It has recently developed a hum issue. On the rear there is an option of disconnecting the Chasis ground from the Circuit ground, as long as the circuit ground is grounded to somewhere else in the sound system. I have tried this by making up an XLR with only the ground connected and plugging that into our sound desk (A&H GL3300). Then connecting the inputs and outputs to the terminal connections on the back rather than XLR or Jacks. We still seem to get the hum. Am I missing something here in the connections or could it be a fault with the EQ internals?

 

 

 

Thanks

 

 

 

Mick

[vlfaudio]

The earth lift will work using normal XLR leads, if the hum persists, check if pin 1 has been linked to the XLR barrel, remove the link if this is the case.

Try changing the IEC power lead. Check the mains plug for loose connections. Check the plugboard it is plugged into for loose connections.

[Oldradiohand]

Unplug everything but the mains, use a pair of headphones (with a suitable adaptor, set of croc clips or bare wires) and listen to the output of the box. Is it clean? No? probably a burgered power supply. Yes? as it's only happened recently, think about what might have changed to cause it. Try using the headphones to listen to the connected input to the DBX., then the out put unconnected, then the output connected. Try removing stuff you've recently added or replugged and see if the hum goes away.

[vlfaudio]

As Oldradiohand says, it's likely you've changed or added something recently that may have seemed innocuous. Had an old Soundcraft Spirit in a venue that developed a hum after the IEC mains lead to the PSU was changed; the contacts in moulded mains connectors get worn/bent/tarnished over time. One dodgy cable or piece of equipment can stuff up the signal ground, disconnect all the inputs/outputs apart from FOH and check for hum, add stuff one at a time till you find the culprit.