I have a new addition to my bodge-it tool kit! It was something I didn’t need until I had to solve a problem I had never had before.
I am currently out doing festivals with my trusty analogue mixing desk. As we are doing lots of shows I am using locally-supplied multicores at each festival. This is problematical but we have a nice split system and as long as we take the mains for FOH from the same place as monitors it is not normally an issue.
Last week we did two back-to-back festivals. First day, no problem! Second day, almost identical set of equipment - huge buzz on the desk. Being analogue everyone started telling me what a mistake this was, it always buzzes, what do you expect! Well maybe? It had worked the day before but you never know.
Tom, my long suffering assistant, spent the next 30 minutes climbing under the stage locating power cables, earths, possible ground loops... nothing! I disconnecting my desk from the house and this stopped the hum. Earth lifting my desk made no difference. Luckily I carry earth lift cables as well as transformer isolators. We tried everything at the desk end, no joy! Now the only thing I had changed from the previous year was adding my own analogue to digital converter so I can give the PA company an AES signal. Could it be that?
Well I knew I couldn’t use my isolating transformer but would a simple earth lift work? We lifted the sends from the processor and….. clean! It worked and was quiet. In retrospect it may have been down to the fact that all the other desks were digital and everything was running off a UPS. My desk had the only real ground.
I now have a digital grade isolating transformer! It’s expensive but when you have precious little time being able to put it inline and see if the problem changes can really help. Be prepared, carry a few handy connectors and adaptors! You never know when they may come in handy.
And the buzz? It was the digital not the analogue bit causing the problem!