# Electronic Crossover suddenly develops hum



## sportflyer (May 2, 2010)

I am not sure this is the right Forum to ask for help re Xover. 

I have been using the Energy EAC Crossover for many months. This morning , I decided to bypass the Xover so I made some interconnect changes. After testing my speakers without Xover , I reconnected the Xover and now suddenly I get a loud 120Hz hum. With the Xover unit out of the loop and Preamp connected to power amp , I get no hum. As soon as I connect the Xover output to the power amp the hum reappears. Any idea what has happened? I have not changed any of the mains power connection so it cant be ground loop. 

If power bug ( AC 16V) is removed from the Xover unit there is no hum even with Power amp connected. Hum immediately appears when power is applied to Xover with no inputs connected. ( ie just Xover and Poweramp) 

I opened the Xover unit and resoldered the input /output RCA connectors to the PS Bd , thinking it could be a bad solder joint but unfortunately this did not solve the problem. 

Finally I probed the unit with an Oscilloscope and noticed quite a ripple on the + Line after the first rectifiier cap ( 2200UF, 25V) . Could this be the culprit? I wonder how often a Lytic Cap goes bad. 

Any other ideas? 

Tks


Replacing filter cap reduced the ripple but did not solve the problem. After looking very closely at the I/O RCA block, I found that the output RCA connectors did not have a ground connection to the PC BD ( which caused the hum ) Resoldering the pin did not fix the problem because I think the ground connection was broken between the pin and the RCA Connector grounds internally ( probably over stressed when plugging and unplugging the interconnects.) Fortunately there was another place between the L/R output that I can solder a piece of hookup wire and then ground that to the PC ground . The access point between the output RCA connectors saved me having to remove the whole block ( nine connections) 

Now all is fine


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## robbo266317 (Sep 22, 2008)

I'm glad you found the issue, I was going to suggest checking your leads as well with a multimeter from end to end.

Nice troubleshooting.


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## sportflyer (May 2, 2010)

Thanks. I think I will increase the filter cap to 3300UF or higher to reduce the ripple a bit more.


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